Researchers have found that a previous SARS-CoV-2 infection is not as effective in preventing re-infection with the Omicron variant. This study was reported in the New England Journal of Medicine after reviewing national data from Qatar.
This finding was linked to the Omicron variant’s ability to mutate multiple times evading the body’s immune system. The researchers employed a test-negative, case–control study design for the assessment.
The research showed that previous COVID-19 infection protects against Omicron reinfection only 56% of the time. On the other hand, previous COVID-19 infection was 90.2% effective against reinfection with the Alpha variant, 85.7% effective against the Beta variant reinfection, and 92% effective against Delta reinfection.
According to the researchers, “the protection of previous infection against hospitalisation or death caused by reinfection (with Omicron) appeared to be robust.” This is because in cases of critical or fatal COVID-19 re-infection, the immune response was 87.8% effective in preventing the second infection (with Omicron) from progressing to severe or critical illness or death. This same observation was made with the other variants where the effectiveness with respect to severe, critical, or fatal Covid-19 was estimated to be 69.4% against the alpha variant, 88.0% against the beta variant, and 100% against the delta variant.
This research is one of the most recent studies evaluating the COVID-19 and immune response. It is yet to be certified by peer review.