Three-dose vaccine or 2 doses + previous infection protect against severe disease from BA.1 or BA.2 COVID-19 variants

Référence

Altarawneh HN, Chemaitelly H, Ayoub HH, et al. Effects of previous infection and vaccination on symptomatic omicron infections. N Engl J Med 2022;387(1):21-34.

Sommaire

This study was done in Qatar, which has a diverse, young population that includes many guest workers from south and east Asia. Only 9% are older than 50 years. This study looked at symptomatic COVID-19 infections between December 23, 2021, and February 21, 2022. They used a case-control, test-negative design, matching each confirmed person with symptomatic COVID-19 with a control person who had not been infected. The researchers evaluated the following for protection during the initial omicron wave with the BA.1 and BA.2 variants: infection with a variant prior to the omicron wave, 2 doses of mRNA vaccine, 3 doses of mRNA vaccine, and hybrid immunity in patients with 2 or 3 doses of vaccine and a previous infection. For those who received 2 doses, the median interval from the second dose to PCR test was 268 days, while that interval was only 42 days for patients who received a third dose. Protection from symptomatic infection was 50.8% for previous infection without vaccine, 0% for 2 doses of vaccine (mostly given at least 6 months ago) and no previous infection, 55.5% for 2 doses of vaccine and previous infection, 54.0% for 3 doses of vaccine, and 76.3% for 3 doses of vaccine plus a previous infection. The authors did not evaluate 4 doses of vaccine. The good news is that protection against severe, critical, or fatal COVID-19 was much better: 71.6% for previous infection only, 73.5% for 2 doses and no previous infection, 94.3% for 2 doses and previous infection, 92.5% for 3 doses and no previous infection, and 100% for 3 doses and previous infection.