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Published on: June 5, 2021
SARS-CoV-2 seropositivity and subsequent infection risk: a prospective cohort study
Dr Mohamed Ahmed Syed1, Dr Ahmed Sameer Alnuaimi1, Dr Hamda Abdulla A/Qotba1
1Department of Clinical Research, Directorate of Clinical Affairs, Primary Health Care Corporation, PO Box 26555, Doha, Qatar.
Objectives:
This aim of this study was to examine the relationship between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seropositivity and subsequent infection.
Design:
A cohort study design was employed.
Methods:
Stratified random sampling was undertaken to identify individuals aged 10 years and above registered with Qatar's largest primary healthcare provider. A questionnaire was administered, and blood samples were collected and analyzed for immunoglobulin G antibodies against SARS-CoV-2 at baseline. Participants were followed up until March 31, 2021 (a 34-week follow-up period) for vaccination status and a positive polymerase chain reaction (PCR) test for SARS-CoV-2.
Results:
A total of 2044 individuals participated in the study (97.2% of the planned sample). Of these, 185 (9%) were found to be seropositive at baseline. 450 individuals were vaccinated during the follow-up period - 246 with one dose and 204 with two doses. 86 (4.2%) individuals had a positive PCR test during the follow-up period, of which 80 (3.9%) were seronegative and six (0.3%) were seropositive (five undiluted and one with a titer ≥ 1:8).
Conclusions:
Overall, the findings suggest that reinfections are uncommon. Antibody concentrations potentially influence the risk of subsequent infection. Therefore, it might not be necessary to subject seropositive individuals to vaccination and the quarantine policies that apply to seronegative individuals.
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