Immunity due to Covid-19 coupled with vaccine-induced immunity offers better protection against symptomatic infection, hospitalization or death among individuals with previous SARS-CoV-2 infection, suggests a new study published in The Lancet Infectious Diseases.¹

This study was conducted in Brazil with the objective to analyze the effectiveness of four COVID-19 vaccines - Sinovac, Johnson & Johnson, AstraZeneca and Pfizer-BioNTech - in preventing symptomatic infection, hospitalization and death in persons who had had prior confirmed Covid-19. For this, the researchers utilized the national Covid-19 databases to identify 213,457 individuals who had undergone RT PCR at least 90 days after their initial infection for symptomatic illness. Of these, 30,910 (14.5%) participants tested positive and were designated as reinfection; 22,566 of them were matched with 68,426 individuals who had tested negative and acted as the control group. Women comprised 60% of the study population and their median age was 36 years.

Amongst the cases, nearly 65% were unvaccinated, while in the control group 57% were unvaccinated at the time of the test. A total of 39,717 subjects were vaccinated; 43% had taken CoronaVac, 40% AstraZeneca, 15% were vaccinated with Pfizer vaccine, while 2% had received the J&J vaccine.

After the administration of one dose, the vaccine effectiveness against symptomatic SARS-CoV-2 reinfection at ≥14 days of Pfizer vaccine was 45%, 34% for AstraZeneca, 19% for Coronavac and 44% for the single dose J&J vaccine. After two doses, the vaccine effectiveness against symptomatic SARS-CoV-2 reinfection 14 or more days after completion of the primary vaccination series increased to 64.8% for Pfizer vaccine, 56% for AstraZeneca and 39.4% for CoronaVac.

Similarly, after the administration of one dose, the vaccine effectiveness against Covid-related hospitalization or death at ≥14 days of Pfizer vaccine was 61.8%%, 57% for AstraZeneca, 35% for Coronavac and 58% for the single dose J&J vaccine. After the second dose, the vaccine effectiveness after14 or more days was more than 80% for AstraZeneca, Pfizer and CoronaVac. It was almost 90% for AstraZeneca, 89.7% for the Pfizer vaccine, 81.3% for CoronaVac.

In a subgroup analysis, the effectiveness of the vaccine was also assessed by time from initial positive test to vaccination (91–180 days vs 181–613 days). Only the Pfizer vaccine showed a significant increase in effectiveness against symptomatic disease when given 180 days after the first infection (70.7%) versus 91-180 days (35.3%). While a non-significant increase in effectiveness against symptomatic infection was noted for the other three vaccines for these periods.

This study reiterates the benefits of hybrid immunity obtained from natural infection and vaccination. All four vaccines evaluated in this study were protective against symptomatic illness and hospitalization and/or death in individuals with previous SARS-CoV-2 infection. The second dose of CoronaVac, Pfizer and AstraZeneca provided extra protection. The benefits of vaccination outweigh the risks. Hence, all such individuals should be given the full course of Covid-19 vaccine.

Reference

1. Thiago Cerqueira-Silva, et al. Effectiveness of CoronaVac, ChAdOx1 nCoV-19, BNT162b2, and Ad26.COV2.S among individuals with previous SARS-CoV-2 infection in Brazil: a test-negative, case-control study. The Lancet Infectious Diseases. March 31, 2022 DOI: https://doi.org/10.1016/S1473-3099(22)00140-2.