BNT162b2 mRNA COVID-19 against symptomatic Omicron infection following a mass vaccination campaign in southern Brazil: A prospective test-negative design study.

Background: Evidence regarding effectiveness of BNT162b2 mRNA COVID-19 vaccine against Omicron in Latin America is limited. We estimated BNT162b2 effectiveness against symptomatic COVID-19 in Brazil when Omicron was predominant.
Methods: This prospective test-negative, case-control study was conducted in Toledo, Brazil, following a mass COVID-19 vaccination with BNT162b2. Patients were included if they were aged ≥12 years, sought care for acute respiratory symptoms in the public health system between November 3, 2021 and June 20, 2022, and were tested for SARS-CoV-2 using RT-PCR. In the primary analysis, we determined the effectiveness of two doses of BNT162b2 against symptomatic COVID-19.
Results: A total of 4,574 were enrolled; of these, 1,758 patients (586 cases and 1,172 controls) were included in the primary analysis. Mean age was 27.7 years, 53.8 % were women, and 90.1 % had a Charlson comorbidity index of zero. Omicron accounted for >97 % of all identified SARS-CoV-2 variants, with BA.1 and BA.2 accounting for 84.3 % and 12.6 %, respectively. Overall adjusted estimate of two-dose vaccine effectiveness against symptomatic COVID-19 was 46.7 % (95 %CI, 19.9 %-64.6 %) after a median time between the second dose and the beginning of COVID-19 symptoms of 94 days (IQR, 60-139 days). Effectiveness waned from 77.7 % at 7-29 days after receipt of a second dose to <30 % (non-significant) after ≥120 days.
Conclusion: In a relatively young and healthy Brazilian population, two doses of BNT162b2 provided protection against symptomatic Omicron infection. However, this protection waned significantly over time, underscoring the need for boosting with variant-adapted vaccines in this population prior to waves of disease activity.
Trial Registration Number: ClinicalTrials.gov number, NCT05052307 (https://clinicaltrials.gov/ct2/show/NCT05052307).
Competing Interests: Declaration of Competing Interest Rosa reports honoraria fee related to investigator activities from Pfizer, and research grants from Pfizer and Brazilian Ministry of Health. Falavigna reports honoraria fee related to investigator activities from Pfizer, consulting fees from Sanofi, Ultragenyx,Novartis, Alnylam, PTC and JCR, and honoraria for lectures from Janssen, Abbvie, Sanofi, Roche, Pfizer and Novartis. Manfio, Araujo, Cohen, Barbosa, Paula de Souza, Silva, Sganzerla, da Silva, Ferreira, Rodrigues, Maltempi de Souza de Souza, Oliveira, Gradia, Brandalize, Royer, and Luiz report honoraria fee for working in this study from Hospital Moinhos de Vento. Valluri, Srivastava, Julião, Melone, Allen, Kyaw, Spinardi, Castillo, and McLaughlin are Pfizer empolyees. Kucharski, and Pedrotti have nothing to disclose.
(Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)