Significant neutralizing escapes of Omicron and its sublineages in SARS‐CoV‐2‐infected individuals vaccinated with inactivated vaccines

In China, most SARS‐CoV‐2‐infected individuals had been vaccinated with inactivated vaccines. However, little is known about their immune resistances to the previous variants of concerns (VOCs) and the current Omicron sublineages. Here, we collected convalescent serum samples from SARS‐CoV‐2‐infected individuals during the ancestral, Delta, and Omicron BA.1 waves, and evaluated their cross‐neutralizing antibodies (nAbs) against the previous VOCs and the current Omicron sublineages using VSV‐based pseudoviruses. In the convalescents who had been unvaccinated and vaccinated with two doses of inactivated vaccines, we found infections from either the ancestral or the Delta strain elicited moderate cross‐nAbs to previous VOCs, but very few cross‐nAbs to the Omicron sublineages, including BA.1, BA.2, BA.3, and BA.4/5. The individuals who had been vaccinated with two doses of inactivated vaccines before Omicron BA.1 infection had moderate nAbs to Omicron BA.1, but weak cross‐nAbs to the other Omicron sublineages. While three doses of inactivated vaccines followed Omicron BA.1 infection induced elevated and still weak cross‐nAbs to other Omicron sublineages. Our results indicate that the Omicron sublineages show significant immune escape in the previously SARS‐CoV‐2‐infected individuals and thus highlights the importance of vaccine boosters in this population.