SARS-CoV-2 seroprevalence in Portugal following the third epidemic wave: results of the second National Serological Survey (ISN2COVID-19).

SARS-CoV-2; CORONAVIRUS diseases; SEROPREVALENCE; H7N9 Influenza

Integrated approaches to surveillance of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection are important for public health actions. The 2nd National Serological Survey (ISN2COVID-19) aimed to characterize the extent of SARS-CoV-2 infection and vaccine-induced response in the Portuguese population following the third epidemic wave and the launch of the vaccination campaign. A cross-sectional study was performed using data on 8463 Portuguese 1–79 years of age, collected in February and March, 2021. SARS-CoV-2 IgM and IgG (anti-nucleoprotein and anti-spike) antibodies were determined in serum samples using Abbott Architect chemiluminescent microparticle assays. Post-infection and vaccine-induced seroprevalence with 95% confidence intervals (95%CI) were estimated in the overall sample and stratified by population characteristics. The estimated seroprevalence was 15.5% (95%CI:14.6–16.5%), of which 13.5% (95%CI: 12.6–14.4%) was attributable to natural infection and 2.0% (95%CI:1.7–2.4%) to vaccination. The lowest seroprevelence was observed in persons aged 70–79 years (8.9% 95%CI:6.8–11.6), while seroprevalence in children (14.3%; 95%CI:11.5–17.6%) and adolescents (12.9%; 95%CI:10.5–15.7%) was similar to that of persons aged between 20 and 69 years. Of seropositive individuals, 22.6% (95%CI:19.7–25.9%) did not report any symptoms in 6 months prior to interview. Of persons with completed vaccination (2-doses), 98.6% (95%CI: 93.0–99.7%) had specific IgG (anti-S) antibodies. After the third epidemic wave, the post-infection SARS-CoV-2 seroprevalence was 1.7 times higher than the cumulative incidence based on PCR-testing, but was higher (2.7 times) in children may be due to the high proportion of asymptomatic and mild infections. [ABSTRACT FROM AUTHOR]

Copyright of Infectious Diseases is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)