Fig. 1. Inhibition of omicron pseudoviruses by vaccinated sera.

Sera were collected from two groups of vaccinated people. In one of the groups, ten people received two doses of the Pfizer mRNA spike vaccine. In the other group, ten people received three doses of the same vaccine. SARS-CoV-2 pseudoviruses were used to infect HEK293T cells stably expressing human ACE2 in the presence of serially diluted sera. NT₅₀ values (neutralization titer that inhibits pseudovirus entry by 50%) were calculated for sera from each person. All the measurements were carried out in triplicates. The values are presented as mean plus standard error of the mean (SEM). A Student’s two-tailed t test was performed to analyze the statistical differences among the noted groups. ***P < 0.001; **P < 0.01. The experiments were repeated three times with similar results.