Omicron-Infected People Also Mount Strong Resistance to Delta, Study Finds

People vaccinated against COVID-19 who get an Omicron infection appear to have a low risk of Omicron reinfection, as well as significantly increased resistance to the Delta variant, new South African data suggest.

However, immune response varies widely among unvaccinated people, suggesting that they may be susceptible to repeat Omicron infections as well as Delta reinfection, according to Alex Sigal, a virologist at the Africa Health Research Institute, Durban.

Sigal’s study was very small — just 15 people — and results haven’t been independently reviewed. But the paper, posted on the MedRxiv.com preprint server, found that Omicron infection increased immunity against Omicron reinfection by 14-fold and immunity against Delta by 4.4-fold.