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BackgroundEvaluation of COVID-19 vaccine booster effectiveness is essential as new variants of SARS-CoV-2 emerge. Data support the effectiveness of boosters in preventing severe disease and hospitalization; however, the real-world impact on reducing incident SARS-CoV-2 infections across specific variants is not yet clear. ObjectivesAssess the impact of COVID-19 boosters on protection against SARS-CoV-2 infection in a real-world setting from a highly vaccinated (99%) population curated from a linked database with test results, vaccination history, patient demographics, and genomic sequencing information from the National Basketball Association (NBA). MethodsIn this population, 1,613 fully vaccinated staff and players (median age 34.5 years, 88% male) who tested at least once between 1 December 2021 and 5 January 2022, were analyzed. Individuals were tested at the time of reporting any symptom, regardless of severity, after known exposure per self-report or contact tracing and/or during enhanced surveillance. Boosted individuals (n=1260) were compared to fully vaccinated and booster eligible individuals (n=162), defined as 2 months post-JNJ-78436735 or 5-months post-second dose of mRNA vaccine. Individuals not yet eligible for a booster and those who recovered from COVID-19 between 1 November and 30 November, 2021 (n=25) were examined in secondary analyses but excluded from the primary comparison. Individuals who were not fully vaccinated (n=27) or who received a booster within 14 days during or prior to the observation period (n=916) were excluded. ResultsIn this closely monitored population, fully vaccinated booster-eligible individuals were 2.6 times more likely (RR = 2.6, 95% CI: 2.2 to 3.0, p<0.0001) to have a confirmed COVID-19 infection than boosted individuals. Secondary analysis including non-boosted individuals with recent vaccination or recent SARS-CoV-2 infection found that non-boosted individuals were at greater risk of infection compared with boosted individuals (RR = 2.1, 95% CI: 1.8 to 2.4, p<0.001). Results were similar when stratified by primary vaccination type with overlapping confidence intervals. No hospitalizations or deaths were observed in this cohort. Genetic sequencing confirmed 93% of infections to be Omicron (among n=330 sequenced). ConclusionsThese results highlight the protective benefit of boosters against incident SARS-CoV-19 infection, not only for severe symptoms and death. Assessment of booster effectiveness remains vital for COVID-19 vaccines as new variants of SARS-CoV-2 emerge, as there is still uncertainty around performance in real-world settings. These data are needed to convince the general public that boosters remain effective at preventing in the spread of COVID-19.
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BackgroundThe alpha and delta SARS-CoV-2 variants have been responsible for major recent waves of COVID-19 despite increasing vaccination rates. The reasons for the increased transmissibility of these variants and for the reduced transmissibility of vaccine breakthrough infections are unclear. MethodsWe quantified the course of viral proliferation and clearance for 173 individuals with acute SARS-CoV-2 infections using longitudinal quantitative RT-PCR tests conducted using anterior nares/oropharyngeal samples (n = 199,941) as part of the National Basketball Associations (NBA) occupational health program between November 28th, 2020, and August 11th, 2021. We measured the duration of viral proliferation and clearance and the peak viral concentration separately for individuals infected with alpha, delta, and non-variants of interest/variants of concern (non-VOI/VOC), and for vaccinated and unvaccinated individuals. ResultsThe mean viral trajectories of alpha and delta infections resembled those of non-VOI/VOC infections. Vaccine breakthrough infections exhibited similar proliferation dynamics as infections in unvaccinated individuals (mean peak Ct: 20.5, 95% credible interval [19.0, 21.0] vs. 20.7 [19.8, 20.2], and mean proliferation time 3.2 days [2.5, 4.0] vs. 3.5 days [3.0, 4.0]); however, vaccinated individuals exhibited faster clearance (mean clearance time: 5.5 days [4.6, 6.6] vs. 7.5 days [6.8, 8.2]). ConclusionsAlpha, delta, and non-VOI/VOC infections feature similar viral trajectories. Acute infections in vaccinated and unvaccinated people feature similar proliferation and peak Ct, but vaccinated individuals cleared the infection more quickly. Viral concentrations do not fully explain the differences in infectiousness between SARS-CoV-2 variants, and mitigation measures are needed to limit transmission from vaccinated individuals.
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BackgroundSARS-CoV-2 infections are characterized by viral proliferation and clearance phases and can be followed by low-level persistent viral RNA shedding. The dynamics of viral RNA concentration, particularly in the early stages of infection, can inform clinical measures and interventions such as test-based screening. MethodsWe used prospective longitudinal RT-qPCR testing to measure the viral RNA trajectories for 68 individuals during the resumption of the 2019-20 National Basketball Association season. For 46 individuals with acute infections, we inferred the peak viral concentration and the duration of the viral proliferation and clearance phases. FindingsAccording to our mathematical model, we found that viral RNA concentrations peaked an average of 3.3 days (95% credible interval [2.5, 4.2]) after first possible detectability at a cycle threshold value of 22.3 [20.5, 23.9]. The viral clearance phase lasted longer for symptomatic individuals (10.9 days [7.9, 14.4]) than for asymptomatic individuals (7.8 days [6.1, 9.7]). A second test within 2 days after an initial positive PCR substantially improves certainty about a patients infection phase. The effective sensitivity of a test intended to identify infectious individuals declines substantially with test turnaround time. ConclusionsSARS-CoV-2 viral concentrations peak rapidly regardless of symptoms. Sequential tests can help reveal a patients progress through infection stages. Frequent rapid-turnaround testing is needed to effectively screen individuals before they become infectious.
