SARS-CoV-2 antibody dynamics and transmission from community-wide serological testing in the Italian municipality of Vo’

Abstract

In February and March 2020, two mass swab testing campaigns were conducted in Vo’, Italy. In May 2020, we tested 86% of the Vo’ population with three immuno-assays detecting antibodies against the spike and nucleocapsid antigens, a neutralisation assay and Polymerase Chain Reaction (PCR). Subjects testing positive to PCR in February/March or a serological assay in May were tested again in November. Here we report on the results of the analysis of the May and November surveys. We estimate a seroprevalence of 3.5% (95% Credible Interval (CrI): 2.8–4.3%) in May. In November, 98.8% (95% Confidence Interval (CI): 93.7–100.0%) of sera which tested positive in May still reacted against at least one antigen; 18.6% (95% CI: 11.0–28.5%) showed an increase of antibody or neutralisation reactivity from May. Analysis of the serostatus of the members of 1,118 households indicates a 26.0% (95% CrI: 17.2–36.9%) Susceptible-Infectious Transmission Probability. Contact tracing had limited impact on epidemic suppression.

Performance verification of the Abbott SARS-CoV-2 test for qualitative detection of IgG in Cali, Colombia

“…In our study, sensitivity of the test in the subset of patients >60 days from symptom onset was 88%, indicating that IgG responses can be tracked in individuals during the first two months. This coincides with previous reports of a median half-life of antibodies detected by Abbott of 86 days [ 35 ], and a decay in seropositivity after 90 days reported in a Brazilian population evaluated with this test [ 39 ]. These aspects should be considered when analyzing and interpreting serosurveys conducted globally with the Abbott assay, since the true cumulative number of SARS-CoV-2 infections may be underestimated.…”

“…Decline of antibody titers and seropositivity has been reported for different tests, including the Abbott IgG [ 30 , 35 – 38 ]. In our study, sensitivity of the test in the subset of patients >60 days from symptom onset was 88%, indicating that IgG responses can be tracked in individuals during the first two months.…”

Long-Term Course of Humoral and Cellular Immune Responses in Outpatients After SARS-CoV-2 Infection

“…The team found that 98.8% of people infected in February/March showed detectable levels of antibodies in November, and there was no difference between people who had suffered symptoms of COVID-19 and those who had been symptom-free. The results showed that while all antibody types showed some decline between May and November, the rate of decay was different depending on the assay ( 19 ). Interestingly, after COVID vaccination, neutralization capacity was different from natural infection ( 20 ).…”

The immunology of asymptomatic SARS-CoV-2 infection: what are the key questions?

“…In that study, we found that titres of neutralizing antibodies were sustained at a similarly high, protective level at 4 months after infection, irrespective of symptomatic or asymptomatic disease 52 . Similarly, a longitudinal serological analysis of inhabitants of Vo’ found no difference in antibody responses in individuals with either symptomatic or asymptomatic infection 53 . A 10-month longitudinal analysis of 963 individuals with either symptomatic or asymptomatic disease investigated the durability of neutralizing antibody responses in more detail 54 .…”