Research evaluates the effectiveness of four vaccines in cases of reinfection by COVID-19

A new study by Fiocruz, published in Lancet Infectious Diseases last Thursday (March 31), shows that even people with previous infection by Sars-CoV-2 have higher protection levels when vaccinated. The highest effectiveness was observed with the four vaccines in use in Brazil (Coronavac, AstraZeneca, Janssen, and Pfizer-BioNTech) in the prevention of COVID-19. The research shows increased protection against infection and, in particular, against hospitalization and death of people who had already been infected before taking the vaccine.

Among those who had already been infected prior to vaccination, the effectiveness of the vaccine against hospitalization or death 14 or more days after finishing the vaccination cycle was 81.3% for CoronaVac, 89.9% for AstraZeneca, 57.7% for Janssen, and 89.7% for Pfizer.

These data emphasize the fact that all four vaccines provide additional protection against severe outcomes of COVID-19. In addition, providing a complete series of vaccines to individuals after recovering from COVID-19 may reduce morbidity and mortality.

To get to this conclusion, the researchers used the test-negative design (TND) methodology, with control cases. Based on national figures on notification, hospitalization and vaccination for COVID-19, in the period between February 2020 and 11 November 2021, the researchers identified 213,457 people who had experienced symptomatic disease and who were tested with RT-PCR at least 90 days after the initial infection by Sars-CoV-2 and after the beginning of the vaccination program. From these, 14.5% (30,910 people) had reinfection confirmed.

The researchers then compared symptomatic cases of positive RT-PCR with up to 10 members of the control group who had presented symptoms and negative RT-PCR, restricting both groups to tests made at least 90 days after initial infection. After a multivariable conditional logistic regression, they evaluated the chances of positivity of the test and chances of hospitalization or death by COVID-19 according to the vaccination status and the time since the first or second dose of the vaccines.

In addition to Fiocruz, four other Brazilian institutions financed the research: National Council for Scientific and Technological Development (CNPq), Carlos Chagas Filho Foundation of Research Support in the State of Rio de Janeiro (Faperj), and JBS, a private company. The work was also supported by the Carlos III Health Institute, the Spanish Ministry of Science and Innovation, and the government of the Spanish region of Catalonia.