A new laboratory study shows that a previous infection with the original Omicron (BA.1) variant may not provide good protection from reinfection by two recently identified Omicron subvariants, BA.4 and BA.5, in people who are unvaccinated. The results also show that both the Pfizer and J&J vaccines enhance protection against the Omicron subvariants in people who were vaccinated and had a previous Omicron BA.1 infection.

The research was led by Professor Alex Sigal and Khadija Khan at Africa Health Research Institute. For this work they used plasma, which is the component of blood which contains antibodies, from 24 unvaccinated and 15 vaccinated people – all of whom had been infected with the original circulating Omicron virus (BA.1) – and in the lab added live Omicron BA.4 and BA.5. The ability of the antibodies in the plasma to eliminate the viruses was compared – a so-called ‘neutralisation’ test. They found that there is a 7.6-fold (BA.4) and 7.5-fold (BA.5) decrease in the ability of antibodies from a previous Omicron infection in unvaccinated people to neutralise the subvariants. Those who were vaccinated fared better: there was a 3.2-fold (BA.4) and 2.6-fold (BA.5) decrease respectively. Ultimately, neutralisation levels were about five-fold higher for those who were vaccinated, compared to the unvaccinated group.

“BA.4/BA.5 escape, while not as dramatic as Omicron escape from vaccine or Delta immunity, is enough to lead to a new infection wave driven by the subvariants,” said Prof. Sigal. “This is consistent with current surveillance data coming out of South Africa. However, based on our results, it seems unlikely that these subvariants will cause much more severe disease than the previous wave. Our study again shows the protection offered by Covid-19 vaccines in maintaining levels of immunity that at the very least are effective at preventing severe disease.”

Top image: Escape of BA.4 and BA.5 from Omicron/BA.1 elicited immunity. Neutralization of BA.4 (a) or BA.5 (b) compared to BA.1 virus by immunity elicited through BA.1 infection in n=24 unvaccinated participants. Neutralization of BA.4 (c) or BA.5 (d) compared to BA.1 virus by immunity elicited through BA.1 infection in n=15 participants vaccinated either with Pfizer BNT162b2 (n=8) or Johnson and Johnson Ad26.CoV2.S (n=7). Numbers are geometric mean titer (GMT) FRNT50. Dashed line is most concentrated plasma tested. 

Read the paper, which is submitted as a preprint to MedRxiv, here.