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SARS-CoV-2 attack rate and population immunity in southern New England, March 2020 - May 2021.

ABSTRACT: Estimating an infectious disease attack rate requires inference on the number of reported symptomatic cases of a disease, the number of unreported symptomatic cases, and the number of asymptomatic infections. Population-level immunity can then be estimated as the attack rate plus the number of vaccine recipients who had not been previously infected; this requires an estimate of the fraction of vaccines that were distributed to seropositive individuals. To estimate attack rates and population immunity in southern New England, we fit a validated dynamic epidemiological model to case, clinical, and death data streams reported by Rhode Island, Massachusetts, and Connecticut for the first 15 months of the COVID-19 pandemic, from March 1 2020 to May 31 2021. This period includes the initial spring 2020 wave, the major winter wave of 2020-2021, and the lagging wave of lineage B.1.1.7(Alpha) infections during March-April 2021. In autumn 2020, SARS-CoV-2 population immunity (equal to the attack rate at that point) in southern New England was still below 15%, setting the stage for a large winter wave. After the roll-out of vaccines in early 2021, population immunity in many states was expected to approach 70% by spring 2021, with more than half of this immune population coming from vaccinations. Our population immunity estimates for May 31 2021 are 73.4% (95% CrI: 72.9% - 74.1%) for Rhode Island, 64.1% (95% CrI: 64.0% - 64.4%) for Connecticut, and 66.3% (95% CrI: 65.9% - 66.9%) for Massachusetts, indicating that >33% of southern Englanders were still susceptible to infection when the Delta variant began spreading in July 2021. Despite high vaccine coverage in these states, population immunity in summer 2021 was lower than planned due to 34% (Rhode Island), 25% (Connecticut), and 28% (Massachusetts) of vaccine distribution going to seropositive individuals. Future emergency-setting vaccination planning will likely have to consider over-vaccination as a strategy to ensure that high levels of population immunity are reached during the course of an ongoing epidemic.

SUBMITTER: Tran TN

PROVIDER: S-EPMC8669856 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:IntroductionIndia experienced two waves of Coronavirus disease 2019 (COVID-19) pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 [SARS-CoV-2] and reported second highest caseload globally. Seroepidemiological studies were done to track the course of the pandemic. We systematically reviewed and synthesized seroprevalence of SARS-CoV-2 among Indian population.MethodsWe included studies reporting seroprevalence of IgG antibodies against SARS-CoV-2 from March 1, 2020, to August 11, 2021 and excluded studies done only among COVID-19 patients, and vaccinated individuals. We searched published databases, preprint servers and government documents using a combination of keywords and Medical subheading (MeSH) terms of "Seroprevalence AND SARS-CoV-2 AND India". We assessed risk of bias using the Newcastle Ottawa scale, the Appraisal tool for cross-sectional studies (AXIS), the Joanna Briggs Institute (JBI) critical appraisal tool and WHO's statement on the Reporting of Seroepidemiological Studies for SARS-CoV-2 (ROSES-S). We calculated pooled seroprevalence along with 95% Confidence Intervals (CI) during the first (March 2020 to February 2021) and second wave (March to August 2021). We also estimated seroprevalence by selected demographic characteristics.ResultsWe identified 3821 studies and included 53 studies with 905,379 participants after excluding duplicates, screening of titles and abstracts and full-text screening. Of the 53, 20 studies were of good quality. Some of the reviewed studies did not report adequate information on study methods [sampling=24% (13/53); laboratory=83% (44/53)]. Studies of 'poor' quality had more than one of the following issues: unjustified sample size, non-representative sample, non-classification of non-respondents, results unadjusted for demographics and methods insufficiently explained to enable replication. Overall pooled seroprevalence was 20.7% in the first (95% CI=16.1 to 25.3) and 69.2% (95% CI=64.5 to 73.8) in the second wave. Seroprevalence did not differ by age in first wave, whereas in second, it increased with age. Seroprevalence was slightly higher among females in second wave. In both the waves, the estimate was higher in urban than in rural areas.ConclusionSeroprevalence increased by threefold between the two waves of the pandemic in India. Our review highlights the need for designing and reporting studies using standard protocols.

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SARS-CoV-2 attack rate and population immunity in southern New England, March 2020 - May 2021.

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