key: cord-0031670-h8jwm8y3
authors: Cerqueira-Silva, Thiago; de Araujo Oliveira, Vinicius; Paixão, Enny S; Florentino, Pilar Tavares Veras; Penna, Gerson O; Pearce, Neil; Werneck, Guilherme L; Barreto, Maurício L; Boaventura, Viviane S; Barral-Netto, Manoel
title: Vaccination plus previous infection: protection during the omicron wave in Brazil
date: 2022-05-16
journal: Lancet Infect Dis
DOI: 10.1016/s1473-3099(22)00288-2
sha: 6073a45ce2424d094c08bcbbe1b65d3bce37c2c5
doc_id: 31670
cord_uid: h8jwm8y3

nan

As of May 11, 2022, an estimated 519 million individuals have been infected with SARS-CoV-2, and at least 11 billion COVID-19 vaccine doses have been administered worldwide. Therefore, understanding hybrid immunity (ie, immunity derived from infection plus vaccination) is crucial to guide future vaccination policies. We found that vaccination provided additional protection to that induced by past infection during the gamma (P.1) and delta (B.1.617.2) variant waves of the pandemic in Brazil. 1 With the emergence of the omicron (B.1.1.529) variant, vaccine effectiveness appears to decay, 2,3 but protection in individuals who have been previously infected and vaccinated remains unknown. We analysed the effect of hybrid immunity in preventing infection and severe outcomes during circulation of the omicron variant in Brazil.

Using national databases, we did a test-negative case-control study as previously described. 1 Cases were defined as individuals with positive RT-PCR or lateral-flow tests and controls as individuals with negative RT-PCT or lateral-flow tests between Jan 1 and March 22, 2022-a period during which omicron was the predominant variant in Brazil (appendix pp 2-4). Severe outcomes were defined as a positive test obtained from 14 days before to 3 days after hospital admission or death occurring within 28 days after a positive test. We analysed vaccine effectiveness in individuals who had been previously infected using two references groups: unvaccinated with or without previous infection. Individuals could have more than one test included in these analyses, and each test was separately counted as a case or control. Detailed methods, including full inclusion and exclusion criteria, are in the appendix (p 2).

Of 9 to 62·7% (61·0-64·3), once again waning over time, and substantial protection against severe outcomes after the booster (appendix pp 5, 8-9). Similar results were obtained using a matched analysis by date of test (within 10 days), age (5-year bands), municipality of residence, and sex in a ratio of 1:2 (with replacement; appendix pp 10-12).

In summary, during a period when omicron was the dominant SARS-CoV-2 variant in Brazil, robust protection against severe disease was offered by a previous infection, and this was increased with hybrid immunity. However, against symptomatic infection, even boosted individuals with hybrid immunity had low levels of protection and protection waned over time. Booster doses in previously infected individuals offered a moderate but transient increase in protection against symptomatic infection and a slight improvement against severe outcomes. These data highlight an issue of whether future efforts should focus on preventing symptomatic infection or severe disease, considering the moderate and transient increase in protection offered by boosters against symptomatic infection and the likely endemicity of SARS-CoV-2. 

Effectiveness of COVID-19 vaccines against omicron and delta hospitalisation: test negative case-control study

Effectiveness of CoronaVac, ChAdOx1 nCoV-19, BNT162b2, and Ad26.COV2.S among individuals with previous SARS-CoV-2 infection in Brazil: a test-negative, casecontrol study

COVID-19 vaccine effectiveness against the omicron (B.1.1.529) variant