As part of the response to the highly pathogenic avian influenza A(H5N1) virus outbreak in U.S. cattle and poultry and the associated human cases, CDC and partners are monitoring influenza A virus levels and detection of the H5 subtype in wastewater. Among 48 states and the District of Columbia that performed influenza A testing of wastewater during May 12-July 13, 2024, a weekly average of 309 sites in 38 states had sufficient data for analysis, and 11 sites in four states reported high levels of influenza A virus. H5 subtype testing was conducted at 203 sites in 41 states, with H5 detections at 24 sites in nine states. For each detection or high level, CDC and state and local health departments evaluated data from other influenza surveillance systems and partnered with wastewater utilities and agriculture departments to investigate potential sources. Among the four states with high influenza A virus levels detected in wastewater, three states had corresponding evidence of human influenza activity from other influenza surveillance systems. Among the 24 sites with H5 detections, 15 identified animal sources within the sewershed or adjacent county, including eight milk-processing inputs. Data from these early investigations can help health officials optimize the use of wastewater surveillance during the upcoming respiratory illness season.

Nonpharmaceutical interventions (NPIs) for SARS-CoV-2 disrupted circulation of influenza. We used data from 13 African countries and generalized linear models to identify associations between levels of NPIs, using the Oxford Stringency Index, and seasonal influenza activity, using parameters derived from 2020-2022 seasonal influenza surveillance. We found that for each step increase in school closings, the average percentage of respiratory specimens testing positive for influenza across the influenza season dropped by 20% (95% CI: 1-38%); no other NPI was significant. These findings may inform interventions to slow influenza circulation in pandemics and possibly during seasonal epidemics.

Before the COVID-19 pandemic, the role of asymptomatic influenza virus infections in influenza transmission was uncertain. However, the importance of asymptomatic infection with SARS-CoV-2 for onward transmission of COVID-19 has led experts to question whether the role of asymptomatic influenza virus infections in transmission had been underappreciated. We discuss the existing evidence on the frequency of asymptomatic influenza virus infections, the extent to which they contribute to infection transmission, and remaining knowledge gaps. We propose priority areas for further evaluation, study designs, and case definitions to address existing knowledge gaps.

BACKGROUND: Highly pathogenic avian influenza A(H5) human infections are a global concern, with many A(H5) human cases detected in Vietnam, including a case in October 2022. Using avian influenza virus surveillance from March 2017-September 2022, we described the percent of pooled samples that were positive for avian influenza A, A(H5), A(H5N1), A(H5N6), and A(H5N8) viruses in live bird markets (LBMs) in Vietnam. METHODS: Monthly at each LBM, 30 poultry oropharyngeal swab specimens and five environmental samples were collected. Samples were pooled in groups of five and tested for influenza A, A(H5), A(H5N1), A(H5N6), and A(H5N8) viruses by real-time reverse-transcription polymerase chain reaction. Trends in the percent of pooled samples that were positive for avian influenza were summarized by LBM characteristics and time and compared with the number of passively detected avian influenza outbreaks using Spearman's rank correlation. RESULTS: A total of 25,774 pooled samples were collected through active surveillance at 167 LBMs in 24 provinces; 36.9% of pooled samples were positive for influenza A, 3.6% A(H5), 1.9% A(H5N1), 1.1% A(H5N6), and 0.2% A(H5N8). Influenza A(H5) viruses were identified January-December and at least once in 91.7% of sampled provinces. In 246 A(H5) outbreaks in poultry; 20.3% were influenza A(H5N1), 60.2% A(H5N6), and 19.5% A(H5N8); outbreaks did not correlate with active surveillance. CONCLUSIONS: In Vietnam, influenza A(H5) viruses were detected by active surveillance in LBMs year-round and in most provinces sampled. In addition to outbreak reporting, active surveillance for A(H5) viruses in settings with high potential for animal-to-human spillover can provide situational awareness.

BACKGROUND: Domestic influenza vaccine production facilitates a sustainable supply for mitigating seasonal influenza and improves national health security by providing infrastructure and experience for pandemic vaccine production, if needed. METHODS: A Phase III, double blind, randomized controlled trial was conducted from Sep 2019-Oct 2020 in healthy adults 18-64 years in Nakhon Phanom, Thailand. Randomization (3:3:1) compared study vaccine (Tri Fluvac), saline placebo, and an active comparator (licensed vaccine). Primary outcomes were superior efficacy compared to placebo based on RT-PCR-confirmed influenza virus infection within 12 months and non-inferiority compared to active comparator based on immunogenicity (HAI assay) at 28 days. Safety was also assessed. RESULTS: The trial enrolled 4,284 participants (Tri Fluvac = 1,836; placebo = 1,836; active comparator = 612). There were 29 RT-PCR positive influenza infections (10 Tri Fluvac, 5.5/1,000 PY; 19 placebo, 10.4/1,000PY; 0 comparator) for an absolute protective efficacy of 46.4 (95 % CI = -22.0-76.5) compared with placebo, but the power was 43.7 %. Seroconversion difference rates between Tri Fluvac and comparator at Day 28 were 1.74 (95 % CI: -2.77, 6.25), 2.22 (-2.40, 6.84), and -0.57 (-5.41, 4.27) for A(H1N1), A(H3N2), and B strains, respectively. Adverse and severe adverse events occurred in 175 (9.5 %) Tri Fluvac, 177 (10.8 %) placebo, and 66 (10.8 %) comparator arms (p-value = 0.437, Tri Fluvac vs. comparator) CONCLUSIONS: Tri Fluvac was well tolerated, and immunogenicity was non-inferior to the active comparator, meeting U.S. Food and Drug Administration (FDA) criteria for adult vaccine licensure. Few acute respiratory infections were reported during intense COVID-19 pandemic restrictions, resulting in insufficient power to evaluate clinical efficacy.

BACKGROUND: Avian influenza (AI) virus detections occurred frequently in 2022 and continue to pose a health, economic, and food security risk. The most recent global analysis of official reports of animal outbreaks and human infections with all reportable AI viruses was published almost a decade ago. Increased or renewed reports of AI viruses, especially high pathogenicity H5N8 and H5N1 in birds and H5N1, H5N8, and H5N6 in humans globally, have established the need for a comprehensive review of current global AI virus surveillance data to assess the pandemic risk of AI viruses. OBJECTIVE: This study aims to provide an analysis of global AI animal outbreak and human case surveillance information from the last decade by describing the circulating virus subtypes, regions and temporal trends in reporting, and country characteristics associated with AI virus outbreak reporting in animals; surveillance and reporting gaps for animals and humans are identified. METHODS: We analyzed AI virus infection reports among animals and humans submitted to animal and public health authorities from January 2013 to June 2022 and compared them with reports from January 2005 to December 2012. A multivariable regression analysis was used to evaluate associations between variables of interest and reported AI virus animal outbreaks. RESULTS: From 2013 to 2022, 52.2% (95/182) of World Organisation for Animal Health (WOAH) Member Countries identified 34 AI virus subtypes during 21,249 outbreaks. The most frequently reported subtypes were high pathogenicity AI H5N1 (10,079/21,249, 47.43%) and H5N8 (6722/21,249, 31.63%). A total of 10 high pathogenicity AI and 6 low pathogenicity AI virus subtypes were reported to the WOAH for the first time during 2013-2022. AI outbreaks in animals occurred in 26 more Member Countries than reported in the previous 8 years. Decreasing World Bank income classification was significantly associated with decreases in reported AI outbreaks (P<.001-.02). Between January 2013 and June 2022, 17/194 (8.8%) World Health Organization (WHO) Member States reported 2000 human AI virus infections of 10 virus subtypes. H7N9 (1568/2000, 78.40%) and H5N1 (254/2000, 12.70%) viruses accounted for the most human infections. As many as 8 of these 17 Member States did not report a human case prior to 2013. Of 1953 human cases with available information, 74.81% (n=1461) had a known animal exposure before onset of illness. The median time from illness onset to the notification posted on the WHO event information site was 15 days (IQR 9-30 days; mean 24 days). Seasonality patterns of animal outbreaks and human infections with AI viruses were very similar, occurred year-round, and peaked during November through May. CONCLUSIONS: Our analysis suggests that AI outbreaks are more frequently reported and geographically widespread than in the past. Global surveillance gaps include inconsistent reporting from all regions and human infection reporting delays. Continued monitoring for AI virus outbreaks in animals and human infections with AI viruses is crucial for pandemic preparedness.

Transplant recipients are among the groups for whom the updated recommendations for 2020–2021 influenza vaccination should generally be considered essential, notably in the face of the COVID-19 pandemic.

The COVID-19 pandemic and subsequent implementation of nonpharmaceutical interventions (e.g., cessation of global travel, mask use, physical distancing, and staying home) reduced the transmission of some viral respiratory pathogens.1 In the United States, influenza activity decreased in March 2020, was historically low through the summer of 2020,2 and remained low during October 2020–May 2021 (<0.4% of respiratory specimens with positive test results for each week of the season). Circulation of other respiratory pathogens, including respiratory syncytial virus (RSV), common human coronaviruses (HCoVs) types OC43, NL63, 229E, and HKU1, and parainfluenza viruses (PIVs) types 1–4 also decreased in early 2020 and did not increase until spring 2021. Human metapneumovirus (HMPV) circulation decreased in March 2020 and remained low through May 2021. Respiratory adenovirus (RAdV) circulated at lower levels throughout 2020 and as of early May 2021. Rhinovirus and enterovirus (RV/EV) circulation decreased in March 2020, remained low until May 2020, and then increased to near prepandemic seasonal levels. Circulation of respiratory viruses could resume at prepandemic levels after COVID-19 mitigation practices become less stringent. Clinicians should be aware of increases in some respiratory virus activity and remain vigilant for off-season increases. In addition to the use of everyday preventive actions, fall influenza vaccination campaigns are an important component of prevention as COVID-19 mitigation measures are relaxed and schools and workplaces resume in-person activities.

BACKGROUND: Using country-specific surveillance data to describe influenza epidemic activity could inform decisions on the timing of influenza vaccination. We analysed surveillance data from African countries to characterise the timing of seasonal influenza epidemics to inform national vaccination strategies. METHODS: We used publicly available sentinel data from African countries reporting to the WHO Global Influenza Surveillance and Response FluNet platform that had 3-10 years of data collected during 2010-19. We calculated a 3-week moving proportion of samples positive for influenza virus and assessed epidemic timing using an aggregate average method. The start and end of each epidemic were defined as the first week when the proportion of positive samples exceeded or went below the annual mean, respectively, for at least 3 consecutive weeks. We categorised countries into five epidemic patterns: northern hemisphere-dominant, with epidemics occurring in October-March; southern hemisphere-dominant, with epidemics occurring in April-September; primarily northern hemisphere with some epidemic activity in southern hemisphere months; primarily southern hemisphere with some epidemic activity in northern hemisphere months; and year-round influenza transmission without a discernible northern hemisphere or southern hemisphere predominance (no clear pattern). FINDINGS: Of the 34 countries reporting data to FluNet, 25 had at least 3 years of data, representing 46% of the countries in Africa and 89% of Africa's population. Study countries reported RT-PCR respiratory virus results for a total of 503 609 specimens (median 12 971 [IQR 9607-20 960] per country-year), of which 74 001 (15%; median 2078 [IQR 1087-3008] per country-year) were positive for influenza viruses. 248 epidemics occurred across 236 country-years of data (median 10 [range 7-10] per country). Six (24%) countries had a northern hemisphere pattern (Algeria, Burkina Faso, Egypt, Morocco, Niger, and Tunisia). Eight (32%) had a primarily northern hemisphere pattern with some southern hemisphere epidemics (Cameroon, Ethiopia, Mali, Mozambique, Nigeria, Senegal, Tanzania, and Togo). Three (12%) had a primarily southern hemisphere pattern with some northern hemisphere epidemics (Ghana, Kenya, and Uganda). Three (12%) had a southern hemisphere pattern (Central African Republic, South Africa, and Zambia). Five (20%) had no clear pattern (Côte d'Ivoire, DR Congo, Madagascar, Mauritius, and Rwanda). INTERPRETATION: Most countries had identifiable influenza epidemic periods that could be used to inform authorities of non-seasonal and seasonal influenza activity, guide vaccine timing, and promote timely interventions. FUNDING: None. TRANSLATIONS: For the Berber, Luganda, Xhosa, Chewa, Yoruba, Igbo, Hausa and Afan Oromo translations of the abstract see Supplementary Materials section.

A network of global respiratory disease surveillance systems and partnerships has been built over decades as a direct response to the persistent threat of seasonal, zoonotic, and pandemic influenza. These efforts have been spearheaded by the World Health Organization, country ministries of health, the US Centers for Disease Control and Prevention, nongovernmental organizations, academic groups, and others. During the COVID-19 pandemic, the US Centers for Disease Control and Prevention worked closely with ministries of health in partner countries and the World Health Organization to leverage influenza surveillance systems and programs to respond to SARS-CoV-2 transmission. Countries used existing surveillance systems for severe acute respiratory infection and influenza-like illness, respiratory virus laboratory resources, pandemic influenza preparedness plans, and ongoing population-based influenza studies to track, study, and respond to SARS-CoV-2 infections. The incorporation of COVID-19 surveillance into existing influenza sentinel surveillance systems can support continued global surveillance for respiratory viruses with pandemic potential.

BACKGROUND: Seasonal influenza-associated excess mortality estimates can be timely and provide useful information on the severity of an epidemic. This methodology can be leveraged during an emergency response or pandemic. METHOD: For Denmark, Spain, and the United States, we estimated age-stratified excess mortality for (i) all-cause, (ii) respiratory and circulatory, (iii) circulatory, (iv) respiratory, and (v) pneumonia, and influenza causes of death for the 2015/2016 and 2016/2017 influenza seasons. We quantified differences between the countries and seasonal excess mortality estimates and the death categories. We used a time-series linear regression model accounting for time and seasonal trends using mortality data from 2010 through 2017. RESULTS: The respective periods of weekly excess mortality for all-cause and cause-specific deaths were similar in their chronological patterns. Seasonal all-cause excess mortality rates for the 2015/2016 and 2016/2017 influenza seasons were 4.7 (3.3-6.1) and 14.3 (13.0-15.6) per 100,000 population, for the United States; 20.3 (15.8-25.0) and 24.0 (19.3-28.7) per 100,000 population for Denmark; and 22.9 (18.9-26.9) and 52.9 (49.1-56.8) per 100,000 population for Spain. Seasonal respiratory and circulatory excess mortality estimates were two to three times lower than the all-cause estimates. DISCUSSION: We observed fewer influenza-associated deaths when we examined cause-specific death categories compared with all-cause deaths and observed the same trends in peaks in deaths with all death causes. Because all-cause deaths are more available, these models can be used to monitor virus activity in near real time. This approach may contribute to the development of timely mortality monitoring systems during public health emergencies.

BACKGROUND: Low global influenza circulation was reported during the coronavirus-19 pandemic. We explored relationships between non-pharmaceutical interventions (NPIs) and influenza in tropical Asian countries. METHODS: Using World Health Organization (WHO) surveillance data from 2015 to 2019 and the WHO shiny app, we constructed expected seasonal influenza epidemic curves from March 2020 to June 2021 and compared the timing, and average percent positivity with observed data. We used multivariate regression to test associations between ordinal NPI data (from the Oxford Stringency Index) 4 weeks before the expected 2020/21 epidemics and present adjusted incidence rate ratio (IRR) or relative proportion ratio (RPR) and 95% confidence intervals (CI). RESULTS: Data from nine countries predicted 18 seasonal epidemics; seven were observed. Five started 6-24 weeks later, and all were 4-21 weeks shorter than expected. Five epidemics had lower maximum peak values (percent positivity), and all but one had lower average percent positivity than expected. All countries implemented NPIs. Each increased level of school closure reduced risk of an epidemic by 43% (IRR = 0.57, CI: 0.34, 0.95). Each increased level of canceling public events reduced the average percent positivity across the season by 44% (RPR = 0.56, CI: 0.39, 0.82) and each increased level in restricting internal movements reduced it by 41% (RPR = 0.59, CI: 0.36, 0.96). Other NPIs were not associated with changes. CONCLUSIONS: Among nine countries, the 2020/21 seasonal epidemics were delayed, shorter, and less intense than expected. Although layered NPIs were difficult to tease apart, school closings, canceling public events, and restricting internal movements before influenza circulation seemed to reduce transmission.

In March 2021, Lao People's Democratic Republic (Laos) reported an avian influenza A(H5N6) virus infection in a 5-year-old child identified through sentinel surveillance. This was the first human A(H5N6) infection reported outside of China. A multidisciplinary investigation undertook contact tracing and enhanced human and animal surveillance in surrounding villages and live bird markets. Seven Muscovy ducks tested positive for highly pathogenic avian influenza A(H5N6) viruses. Sequenced viruses belonged to clade 2.3.4.4h and were closely related to viruses detected in poultry in Vietnam and to previous viruses detected in Laos. Surveillance and coordinated outbreak response remain essential to global health security.

In February 2021, routine sentinel surveillance for influenza-like illness in Cambodia detected a human avian influenza A(H9N2) virus infection. Investigations identified no recent H9N2 virus infections in 43 close contacts. One chicken sample from the infected child's house was positive for H9N2 virus and genetically similar to the human virus.

The COVID-19 pandemic and subsequent implementation of nonpharmaceutical interventions (e.g., cessation of global travel, mask use, physical distancing, and staying home) reduced transmission of some viral respiratory pathogens (1). In the United States, influenza activity decreased in March 2020, was historically low through the summer of 2020 (2), and remained low during October 2020-May 2021 (<0.4% of respiratory specimens with positive test results for each week of the season). Circulation of other respiratory pathogens, including respiratory syncytial virus (RSV), common human coronaviruses (HCoVs) types OC43, NL63, 229E, and HKU1, and parainfluenza viruses (PIVs) types 1-4 also decreased in early 2020 and did not increase until spring 2021. Human metapneumovirus (HMPV) circulation decreased in March 2020 and remained low through May 2021. Respiratory adenovirus (RAdV) circulated at lower levels throughout 2020 and as of early May 2021. Rhinovirus and enterovirus (RV/EV) circulation decreased in March 2020, remained low until May 2020, and then increased to near prepandemic seasonal levels. Circulation of respiratory viruses could resume at prepandemic levels after COVID-19 mitigation practices become less stringent. Clinicians should be aware of increases in some respiratory virus activity and remain vigilant for off-season increases. In addition to the use of everyday preventive actions, fall influenza vaccination campaigns are an important component of prevention as COVID-19 mitigation measures are relaxed and schools and workplaces resume in-person activities.

BACKGROUND: Influenza illness burden is substantial, particularly among young children, older adults, and those with underlying conditions. Initiatives are underway to develop better global estimates for influenza-associated hospitalizations and deaths. Knowledge gaps remain regarding the role of influenza viruses in severe respiratory disease and hospitalizations among adults, particularly in lower-income settings. METHODS AND FINDINGS: We aggregated published data from a systematic review and unpublished data from surveillance platforms to generate global meta-analytic estimates for the proportion of acute respiratory hospitalizations associated with influenza viruses among adults. We searched 9 online databases (Medline, Embase, CINAHL, Cochrane Library, Scopus, Global Health, LILACS, WHOLIS, and CNKI; 1 January 1996-31 December 2016) to identify observational studies of influenza-associated hospitalizations in adults, and assessed eligible papers for bias using a simplified Newcastle-Ottawa scale for observational data. We applied meta-analytic proportions to global estimates of lower respiratory infections (LRIs) and hospitalizations from the Global Burden of Disease study in adults ≥20 years and by age groups (20-64 years and ≥65 years) to obtain the number of influenza-associated LRI episodes and hospitalizations for 2016. Data from 63 sources showed that influenza was associated with 14.1% (95% CI 12.1%-16.5%) of acute respiratory hospitalizations among all adults, with no significant differences by age group. The 63 data sources represent published observational studies (n = 28) and unpublished surveillance data (n = 35), from all World Health Organization regions (Africa, n = 8; Americas, n = 11; Eastern Mediterranean, n = 7; Europe, n = 8; Southeast Asia, n = 11; Western Pacific, n = 18). Data quality for published data sources was predominantly moderate or high (75%, n = 56/75). We estimate 32,126,000 (95% CI 20,484,000-46,129,000) influenza-associated LRI episodes and 5,678,000 (95% CI 3,205,000-9,432,000) LRI hospitalizations occur each year among adults. While adults <65 years contribute most influenza-associated LRI hospitalizations and episodes (3,464,000 [95% CI 1,885,000-5,978,000] LRI hospitalizations and 31,087,000 [95% CI 19,987,000-44,444,000] LRI episodes), hospitalization rates were highest in those ≥65 years (437/100,000 person-years [95% CI 265-612/100,000 person-years]). For this analysis, published articles were limited in their inclusion of stratified testing data by year and age group. Lack of information regarding influenza vaccination of the study population was also a limitation across both types of data sources. CONCLUSIONS: In this meta-analysis, we estimated that influenza viruses are associated with over 5 million hospitalizations worldwide per year. Inclusion of both published and unpublished findings allowed for increased power to generate stratified estimates, and improved representation from lower-income countries. Together, the available data demonstrate the importance of influenza viruses as a cause of severe disease and hospitalizations in younger and older adults worldwide.

Global influenza virus circulation declined and has been below traditional seasonal levels during the COVID‐19 pandemic. 1 , 2 , 3 After learning of increased influenza virus circulation in some tropical Asian countries, we reviewed current surveillance data to better ascertain risk for an influenza resurgence during the 2020‐2021 Northern Hemisphere influenza season and subsequent seasons during the COVID‐19 pandemic.

BACKGROUND: Coinciding with the COVID-19 pandemic, global influenza virus circulation decreased, possibly due to widespread community mitigation measures. Cambodia eased some COVID-19 mitigation measures in June and July 2020. On Aug 20th a cluster of respiratory illnesses among residents of a pagoda included persons that had tested positive for influenza A, and none that were positive for SARS-CoV-2. METHODS: On Aug 25, a response team deployed. Persons with influenza-like illness (ILI) were asked questions on demographics, illness, personal prevention measures, and residential arrangements. Respiratory swabs were tested for influenza and SARS-Cov-2 by RT-PCR; viruses were sequenced. Sentinel surveillance data were analyzed to assess recent trends in influenza circulation in the community. RESULTS: Influenza A(H3N2) viruses were identified in sentinel surveillance in Cambodia in July 2020, prior to the reported pagoda outbreak. Among the 362 pagoda residents, 73(20.2%) ILI cases were identified; 40 were tested with 33/40 (82.5%) confirmed positive for influenza A(H3N2). All 40 were negative for SARS-CoV-2. Among 73 residents with ILI, none were vaccinated against influenza, 47 (64%) clustered in 3 of 8 sleeping quarters; 20 (27%) reported often wearing a mask; 27 (36%) reported often washing hands; and 11 (15%) reported practicing social distancing. All viruses clustered within clade 3c2.A1 close to strains circulating in Australia in 2020. CONCLUSIONS: Circulation of influenza viruses began in the community following a relaxing of national COVID-19 mitigation measures, and prior to this outbreak in a pagoda with limited social distancing. Continued surveillance and influenza vaccination remain needed to limit the impact of influenza globally.

After recognition of widespread community transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), by mid- to late February 2020, indicators of influenza activity began to decline in the Northern Hemisphere. These changes were attributed to both artifactual changes related to declines in routine health seeking for respiratory illness as well as real changes in influenza virus circulation because of widespread implementation of measures to mitigate transmission of SARS-CoV-2. Data from clinical laboratories in the United States indicated a 61% decrease in the number of specimens submitted (from a median of 49,696 per week during September 29, 2019-February 29, 2020, to 19,537 during March 1-May 16, 2020) and a 98% decrease in influenza activity as measured by percentage of submitted specimens testing positive (from a median of 19.34% to 0.33%). Interseasonal (i.e., summer) circulation of influenza in the United States (May 17-August 8, 2020) is currently at historical lows (median = 0.20% tests positive in 2020 versus 2.35% in 2019, 1.04% in 2018, and 2.36% in 2017). Influenza data reported to the World Health Organization's (WHO's) FluNet platform from three Southern Hemisphere countries that serve as robust sentinel sites for influenza from Oceania (Australia), South America (Chile), and Southern Africa (South Africa) showed very low influenza activity during June-August 2020, the months that constitute the typical Southern Hemisphere influenza season. In countries or jurisdictions where extensive community mitigation measures are maintained (e.g., face masks, social distancing, school closures, and teleworking), those locations might have little influenza circulation during the upcoming 2020-21 Northern Hemisphere influenza season. The use of community mitigation measures for the COVID-19 pandemic, plus influenza vaccination, are likely to be effective in reducing the incidence and impact of influenza, and some of these mitigation measures could have a role in preventing influenza in future seasons. However, given the novelty of the COVID-19 pandemic and the uncertainty of continued community mitigation measures, it is important to plan for seasonal influenza circulation in the United States this fall and winter. Influenza vaccination of all persons aged ≥6 months remains the best method for influenza prevention and is especially important this season when SARS-CoV-2 and influenza virus might cocirculate (1).

Despite recommendations, few children aged 6-35 months in Thailand receive seasonal influenza vaccination. Using previously estimated incidence and vaccine effectiveness data from the period 2012-2014, we estimate that up to 121 000 medical visits could be prevented each year with 50% coverage and expanded recommendations to children aged <5 years.

BACKGROUND: We used data from the Sentinel Enhanced Dengue Surveillance System (SEDSS) to describe influenza trends in southern Puerto Rico during 2012-2018 and compare them to trends in the United States. METHODS: Patients with fever onset </= 7 days presenting were enrolled. Nasal/oropharyngeal swabs were tested for influenza A and B viruses by PCR. Virologic data were obtained from the US World Health Organization (WHO) Collaborating Laboratories System and the National Respiratory and Enteric Virus Surveillance System (NREVSS). We compared influenza A and B infections identified from SEDSS and WHO/NREVSS laboratories reported by US Department of Health and Human Services (HHS) region using time series decomposition methods, and analysed coherence of climate and influenza trends by region. RESULTS: Among 23,124 participants, 9% were positive for influenza A and 5% for influenza B. Influenza A and B viruses were identified year-round, with no clear seasonal patterns from 2012 to 2015 and peaks in December-January in 2016-2017 and 2017-2018 seasons. Influenza seasons in HHS regions were relatively synchronized in recent years with the seasons in Puerto Rico. We observed high coherence between absolute humidity and influenza A and B virus in HHS regions. In Puerto Rico, coherence was much lower in the early years but increased to similar levels to HHS regions by 2017-2018. CONCLUSIONS: Influenza seasons in Puerto Rico have recently become synchronized with seasons in US HHS regions. Current US recommendations are for everyone 6 months and older to receive influenza vaccination by the end of October seem appropriate for Puerto Rico.

BACKGROUND: We measured seroconversion to influenza viruses and incidence of symptomatic influenza virus infection in a cohort of children in Bangkok, Thailand. METHODS: Children aged </=6 months were followed for two years for acute respiratory illness and had serum specimens taken at 6-month intervals and tested by hemagglutination inhibition (HI) assay. Seroconversion was defined as a >4-fold rise in the HI titers between time points with a titer of >40 in the second specimen. Respiratory swabs were tested by rRT-PCR for influenza. Data were analyzed using generalized linear models. RESULTS: Of 350 children, 266 (76%, 147 were healthy and 119 high-risk) had >/=2 serum specimens collected before influenza vaccination. During the 2-year follow-up, 266 children contributed 370 person-years of observation, excluding post-vaccination periods. We identified 32 ARI cases with rRT-PCR-confirmed influenza virus infection (7 infections/100 person-years, 95% confidence interval [CI], 4-11). There were 126 episodes of influenza virus infection, resulting in a seroconversion rate of 35 infections/100 person-years (95% CI, 30-42). Rates in healthy and high-risk children did not differ. CONCLUSIONS: Influenza virus infection is common during the first two years of life among Thai children. A large proportion of infections may not be detected using the ARI case definition.

BACKGROUND: Human immunodeficiency virus (HIV)-infected persons are at a higher risk of severe influenza. Although we have shown that a standard-dose intradermal influenza vaccine versus a standard-dose intramuscular influenza vaccine does not result in differences in hemagglutination-inhibition titers in this population, a comprehensive examination of cell-mediated immune responses remains lacking. METHODS: Serological, antigen-specific B-cell, and interleukin 2-, interferon gamma-, and tumor necrosis factor alpha-secreting T-cell responses were assessed in 79 HIV-infected men and 79 HIV-uninfected men. RESULTS: The route of vaccination did not affect the immunoglobulin A and immunoglobulin G (IgG) plasmablast or memory B-cell response, although these were severely impaired in the group with a CD4+ T-cell count of <200 cells/muL. The frequencies of IgG memory B cells measured on day 28 after vaccination were highest in the HIV-uninfected group, followed by the group with a CD4+ T-cell count of >/=200 cells/muL and the group with a CD4+ T-cell count of <200 cells/muL. The route of vaccination did not affect the CD4+ or CD8+ T-cell responses measured at various times after vaccination. CONCLUSIONS: The route of vaccination had no effect on antibody responses, antibody avidity, T-cell responses, or B-cell responses in HIV-infected or HIV-uninfected subjects. With the serological and cellular immune responses to influenza vaccination being impaired in HIV-infected individuals with a CD4+ T-cell count of <200 cells/muL, passive immunization strategies need to be explored to protect this population. CLINICAL TRIALS REGISTRATION: NCT01538940.

BACKGROUND: The estimated association of maternal influenza vaccination and birth outcomes may be sensitive to methods used to define preterm birth or small-for-gestational age (SGA). METHODS: In a cohort of pregnant women in Lao People's Democratic Republic, we estimated gestational age from: (a) date of last menstrual period (LMP), (b) any prenatal ultrasound, (c) first trimester ultrasound, (d) Ballard Score at delivery, and (e) an algorithm combining LMP and ultrasound. Infants were classified as SGA at birth using a Canadian, global, and equation-based growth reference. We estimated the association of maternal influenza vaccination and birth outcomes, by influenza activity, using multivariable log-binomial regression and Cox proportional hazards regression with vaccination as a time-varying exposure. RESULTS: The frequency of preterm birth in the cohort varied by method to estimate gestational age, from 5% using Ballard Score to 15% using any ultrasound. Using LMP, any ultrasound, or the algorithm, we found statistically significant reductions in preterm birth among vaccinated women during periods of high influenza activity and statistically significant increases in SGA, using a Canadian growth reference. We did not find statistically significant associations with SGA when using global or equation-based growth references. CONCLUSIONS: The association of maternal influenza vaccination and birth outcomes was most affected by the choice of a growth reference used to define SGA at birth. The association with pre-term birth was present and consistent across multiple statistical approaches. Future studies of birth outcomes, specifically SGA, should carefully consider the potential for bias introduced by measurement choice.

In the United States, outbreaks of avian influenza H5 and H7 virus infections in poultry have raised concern about the risk for infections in humans. We reviewed the data collected during 2014-2017 and found no human infections among 4,555 exposed responders who were wearing protection.

BACKGROUND: Rapid reporting of human infections with novel influenza A viruses accelerates detection of viruses with pandemic potential and implementation of an effective public health response. After detection of human infections with influenza A (H3N2) variant (H3N2v) viruses associated with agricultural fairs during August 2016, the Michigan Department of Health and Human Services worked with the US Centers for Disease Control and Prevention (CDC) to identify infections with variant influenza viruses using a text-based illness monitoring system. OBJECTIVE: To enhance detection of influenza infections using text-based monitoring and evaluate the feasibility and acceptability of the system for use in future outbreaks of novel influenza viruses. METHODS: During an outbreak of H3N2v virus infections among agricultural fair attendees, we deployed a text-illness monitoring (TIM) system to conduct active illness surveillance among households of youth who exhibited swine at fairs. We selected all fairs with suspected H3N2v virus infections. For fairs without suspected infections, we selected only those fairs that met predefined criteria. Eligible respondents were identified and recruited through email outreach and/or on-site meetings at fairs. During the fairs and for 10 days after selected fairs, enrolled households received daily, automated text-messages inquiring about illness; reports of illness were investigated by local health departments. To understand the feasibility and acceptability of the system, we monitored enrollment and trends in participation and distributed a Web-based survey to households of exhibitors from five fairs. RESULTS: Among an estimated 500 households with a member who exhibited swine at one of nine selected fairs, representatives of 87 (17.4%) households were enrolled, representing 392 household members. Among fairs that were ongoing when the TIM system was deployed, the number of respondents peaked at 54 on the third day of the fair and then steadily declined throughout the rest of the monitoring period; 19 out of 87 household representatives (22%) responded through the end of the 10-day monitoring period. We detected 2 H3N2v virus infections using the TIM system, which represents 17% (2/12) of all H3N2v virus infections detected during this outbreak in Michigan. Of the 70 survey respondents, 16 (23%) had participated in the TIM system. A total of 73% (11/15) participated because it was recommended by fair coordinators and 80% (12/15) said they would participate again. CONCLUSIONS: Using a text-message system, we monitored for illness among a large number of individuals and households and detected H3N2v virus infections through active surveillance. Text-based illness monitoring systems are useful for detecting novel influenza virus infections when active monitoring is necessary. Participant retention and testing of persons reporting illness are critical elements for system improvement.

Despite global recommendations for influenza vaccination of high-risk, target populations, few low and middle-income countries have national influenza vaccination programs. Between 2012 and 2017, Lao PDR planned and conducted a series of activities to develop its national influenza vaccine program as a part of its overall national immunization program. In this paper, we review the underlying strategic planning for this process, and outline the sequence of activities, research studies, partnerships, and policy decisions that were required to build Laos' influenza vaccine program. The successful development and sustainability of the program in Laos offers lessons for other low and middle-income countries interested in initiating or expanding influenza immunization.

The Arizona Department of Health Services identified unusually high levels of influenza activity and severe complications during the 2015-2016 influenza season leading to concerns about potential increased disease severity compared with prior seasons. We estimated state-level burden and severity to compare across three seasons using multiple data sources for community-level illness, hospitalisation and death. Severity ratios were calculated as the number of hospitalisations or deaths per community case. Community influenza-like illness rates, hospitalisation rates and mortality rates in 2015-2016 were higher than the previous two seasons. However, ratios of severe disease to community illness were similar. Arizona experienced overall increased disease burden in 2015-2016, but not increased severity compared with prior seasons. Timely estimates of state-specific burden and severity are potentially feasible and may provide important information during seemingly unusual influenza seasons or pandemic situations.