RESUMO
BackgroundWaning immunity following administration of mRNA based COVID-19 vaccines remains a concern for many health systems. We undertook a study of SARS-CoV-2 infections, with and without requirement for intensive care to shed more light on the duration of vaccine effectiveness for protection against the need for intensive care. MethodsWe used a matched case-control study design with the study base being all individuals with first infection with SARS-CoV-2 reported in the State of Qatar between 1 Jan 2021 and 20 Feb 2022. Cases were those requiring intensive care while controls were those who recovered without need for intensive care. Vaccine effectiveness against requiring intensive care and number needed to vaccinate (NNV) to prevent one more case of COVID-19 requiring intensive care were computed for the mRNA (BNT162b2 / mRNA-1273) vaccines. ResultsVaccine effectiveness against requiring intensive care was 59% (95% confidence interval [CI], 50 to 76) between the first and second dose and strengthened to 89% (95% CI, 85 to 92) between the second dose and 4 months post the second dose in persons who received a primary course of the vaccine. There was no waning of vaccine effectiveness in the period from 4 to 12 months after the second dose. ConclusionsThis study demonstrates that vaccine effectiveness against requiring intensive care remains robust till at least 12 months after the second dose of mRNA based vaccines.
RESUMO
BackgroundQatar has a population of 2.8 million, over half of whom are expatriate craft and manual workers (CMW). We aimed to characterize the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic in Qatar. MethodsA series of epidemiologic studies were conducted including analysis of the national SARS-CoV-2 PCR testing and hospitalization database, community surveys assessing current infection, ad-hoc PCR testing campaigns in workplaces and residential areas, serological testing for antibody on blood specimens collected for routine clinical screening/management, national Coronavirus Diseases 2019 (COVID-19) death registry, and a mathematical model. ResultsBy July 10, 397,577 individuals had been PCR tested for SARS-CoV-2, of whom 110,986 were positive, a positivity cumulative rate of 27.9% (95% CI: 27.8-28.1%). PCR positivity of nasopharyngeal swabs in a national community survey (May 6-7) including 1,307 participants was 14.9% (95% CI: 11.5-19.0%); 58.5% of those testing positive were asymptomatic. Across 448 ad-hoc PCR testing campaigns in workplaces and residential areas including 26,715 individuals, pooled mean PCR positivity was 15.6% (95% CI: 13.7-17.7%). SARS-CoV-2 antibody prevalence was 24.0% (95% CI: 23.3-24.6%) in 32,970 residual clinical blood specimens. Antibody prevalence was only 47.3% (95% CI: 46.2-48.5%) in those who had at least one PCR positive result, but it was 91.3% (95% CI: 89.5-92.9%) among those who were PCR positive >3 weeks before serology testing. There were substantial differences in exposure to infection by nationality and sex, reflecting risk differentials between the craft/manual workers and urban populations. As of July 5, case severity rate, based on the WHO severity classification, was 3.4% and case fatality rate was 1.4 per 1,000 persons. Model-estimated daily number of infections and active-infection prevalence peaked at 22,630 and 5.7%, respectively, on May 21 and May 23. Attack rate (ever infection) was estimated at 53.5% on July 12. R0 ranged between 1.45-1.68 throughout the epidemic. Rt was estimated at 0.70 on June 15, which was hence set as onset date for easing of restrictions. Age was by far the strongest predictor of severe, critical, or fatal infection. ConclusionsQatar has experienced a large SARS-CoV-2 epidemic that is rapidly declining, apparently due to exhaustion of susceptibles. The epidemic demonstrated a classic susceptible-infected-recovered "SIR" dynamics with a rather stable R0 of about 1.6. The young demographic structure of the population, in addition to a resourced public health response, yielded a milder disease burden and lower mortality than elsewhere.