Enhanced replication of rubella virus (RuV) and replicons by de novo synthesized viral structural proteins has been previously described. Such enhancement can occur by viral capsid proteins (CP) alone in trans. It is not clear whether the CP in the virus particles, i.e., the exogenous CP, modulate viral genome replication. In this study, we found that exogenous RuV CP also enhanced viral genome replication, either when used to package replicons or when mixed with RNA during transfection. We demonstrated that CP does not affect the translation efficiency from genomic (gRNA) or subgenomic RNA (sgRNA), the intracellular distribution of the non-structural proteins (NSP), or sgRNA synthesis. Significantly active RNA replication was observed in transfections supplemented with recombinant CP (rCP), which was supported by accumulated genomic negative-strand RNA. rCP was found to restore replication of a few mutants in NSP but failed to fully restore replicons known to have defects in the positive-strand RNA synthesis. By monitoring the amount of RuV RNA following transfection, we found that all RuV replicon RNAs were well-retained in the presence of rCP within 24 h of post-transfection, compared to non-RuV RNA. These results suggest that the exogenous RuV CP increases efficiency of early viral genome replication by modulating the stage(s) prior to and/or at the initiation of negative-strand RNA synthesis, possibly through a general mechanism such as protecting viral RNA.

BACKGROUND: Third doses of measles-mumps-rubella (MMR) vaccine have been administered during mumps outbreaks and in various non-outbreak settings. The immunogenicity of the rubella component has not been evaluated following receipt of a third dose of MMR vaccine. METHODS: Young adults aged 18-31years with documented two doses of MMR vaccine received a third dose of MMR vaccine between July 2009 and October 2010. Rubella neutralizing antibody titers were assessed before, 1month, and 1year after receipt of a third dose of MMR vaccine. RESULTS: Among 679 participants, 1.8% had rubella antibody titers less than 10 U/ml, immediately before vaccination, approximately 15years after receipt of a second dose of MMR vaccine. One month after receipt of a third dose of MMR vaccine, average titers were 4.5 times higher and >50% of participants had a 4-fold boost. Response was highest among those with titers less than 10 U/ml prior to vaccination (geometric mean titer ratio=18.8; 92% seroconversion) and decreased with increasing pre-vaccination titers. Average titers declined 1year postvaccination but remained significantly higher than pre-vaccination levels. The proportion classified as low-positive antibody levels increased from 3% 1month postvaccination to 24% 1year postvaccination. CONCLUSIONS: Vaccination with a third dose of MMR vaccine resulted in a robust boosting of rubella neutralizing antibody response that remained elevated 1year later. Young adults with low rubella titers are more likely to benefit from a third dose of MMR vaccine.

The Second Year of Life project of the Global Health Security Agenda aims to improve immunization systems and strengthen measles and rubella surveillance, including building laboratory capacity. A new laboratory assessment tool was developed by the Centers for Disease Control and Prevention to assess the national laboratory in Ghana to improve molecular surveillance for measles and rubella. Results for the tool showed that the laboratory is well organized, has a good capacity for handling specimens, has a good biosafety system, and is proficient for diagnosis of measles and rubella by serologic analysis. However, there was little knowledge about molecular biology and virology activities (i.e., virus isolation on tissue culture was not available). Recommendations included training of technical personnel for molecular techniques and advocacy for funding for laboratory equipment, reagents, and supplies.

BACKGROUND: Immunity to rubella virus (RV) is commonly determined by measuring specific immunoglobulin G (RV-IgG). However, RV-IgG results and their interpretation may vary depending on the immunoassay even though most commercial imunoassays (CIAs) have been calibrated against an international standard and results are reported in international units per milliliter (IU/mL). METHODS: A panel of 322 sera collected from pregnant women that pretested negative or equivocal for RV-IgG in a prior test (routine screening) was selected. This panel was tested with two reference tests, immunoblot (IB) and neutralization (Nt), and with 8 CIAs widely used in Europe. RESULTS: IB and Nt gave concordant results on 267/322 (82.9%) sera. Of these, 85 (26.4%) sera were negative and 182 (56.5%) sera were positive for both tests. All 85 IB/Nt-negative samples were classified as negative with all CIAs. Of the 182 IB/Nt-positive samples, 25.3% to 61.5% were classified as equivocal and 6% to 64.8% were classified as positive with the CIAs. Wide variations in IU/ml titers were observed. CONCLUSIONS: In our series, more than half the women considered susceptible to RV based on CIA results, tested positive for RV antibodies by IB/Nt. Our data suggest that: i) sensitivity of CIAs could be increased by considering equivocal results as positive, and ii) the definition of immunity to RV as the 10 IU/mL usual cut-off as well as the use of quantitative results for clinical decisions may warrant reconsideration. A better standardization of CIAs for RV IgG determination is needed.

Rubella remains a social and economic burden due to the high incidence of congenital rubella syndrome (CRS) in some countries. For this reason, an accurate and efficient high-throughput measure of antibody response to vaccination is an important tool. In order to measure rubella-specific neutralizing antibodies in a large cohort of vaccinated individuals, a high-throughput immunocolorimetric system was developed. Statistical interpolation models were applied to the resulting titers to refine quantitative estimates of neutralizing antibody titers relative to the assayed neutralizing antibody dilutions. This assay, including the statistical methods developed, can be used to assess the neutralizing humoral immune response to rubella virus and may be adaptable for assessing the response to other viral vaccines and infectious agents.