BACKGROUND: Preprints are publicly available manuscripts posted to various servers that have not been peer-reviewed. Although preprints have existed since 1961, they have gained increased popularity during the COVID-19 pandemic due to the need for immediate, relevant information. OBJECTIVE: The aim of this study is to evaluate the publication rate and impact of preprints included in the CDC COVID-19 Science Update and assess the performance of the COVID-19 Science Update team in selecting impactful preprints. METHODS: All preprints in the first 100 editions (April 1, 2020 - July 30, 2021) of the Science Update were included in the study. Preprints that were not published were categorized as "unpublished preprints". Preprints that were subsequently published exist in two versions (in a peer-reviewed journal and on the original preprint server) which were analyzed separately and referred to as "peer-reviewed preprint" and "original preprint", respectively. Time-to-publish was the time interval between the date on which a preprint was first posted to the date on which it was first available as a peer-reviewed article. Impact was quantified by Altmetric Attention Score and citation count for all available manuscripts on August 6, 2021. Preprints were analyzed by publication status, rate, and time to publication. RESULTS: Among 275 preprints included in the CDC COVID-19 Science Update during the study period, most came from three servers: medRxiv (n=201), bioRxiv (n=41), and SSRN (n=25), with eight coming from other sources. More than half (152 of 275, 55.3%) were eventually published. The median time-to-publish was 2.31 months (IQR 1.38-3.73). When preprints posted in the last 2.31 months were excluded (to account for the time-to-publish), the publication rate was to 67.8%. Seventy-six journals published at least one preprint from the CDC COVID-19 Science Update and 18 journals published at least three. The median Altmetric Attention Score for unpublished preprints (n=123) was 146 (IQR 22-552) and median citation count of 2 (IQR 0-8); for original preprints (n=152) these values were 212 (IQR 22-1164) and 14 (IQR 2-40), respectively; for peer-review preprints, these values were 265 (IQR 29-1896) 19 (IQR 3-101), respectively. CONCLUSIONS: Prior studies of COVID-19 preprints found publication rates between 5.4% and 21.1%. Preprints included in the CDC COVID-19 Science Update were published at a higher rate than overall COVID-19 preprints, and those that were ultimately published were published within months and received higher attention scores than unpublished preprints. These findings indicate that the Science Update process for selecting preprints appears have done so with high fidelity in terms of their likelihood to be published and impactful. Incorporation of high-quality preprints into the CDC COVID-19 Science Update improves this activity's capacity to inform meaningful public health decision making.