Vaccine effectiveness
The vaccine effectiveness of any vaccine in preventing SARS-CoV-2 Omicron BA.2 variant infection is shown in Table 3 and Figure 2. The overall adjusted VE was 35.0% (95% CI: −9.1–61.3%) against infection with any vaccine. Partial and full vaccination provided no protection. Adjusted VE was found to be 51.6% (95% CI: 15.2–72.4%) in the booster vaccination group for preventing Omicron variant infection. The adjusted VE for each type of COVID-19 vaccine differed, and was 65.8% (95% CI: 12.8–86.6%) in the Ad5-nCoV vaccine group, 35.5% (95% CI: −8.6–61.7%) in the inactivated vaccine group, and 13.0% (95% CI: −76.1–57.0%) in the recombinant protein vaccine group. There was no protection for males and the adjusted VE was 55.1% (95 CI: 9.6–77.7%) in the female group. The adjusted VE was not significant different between the two age groups. Comparing the time since vaccination, 48.1% of the case group and 38.3% of the control group were more than 6 months from the last dose of vaccination to exposure. The adjusted VEs were 14.2% (95% CI: −46.9–49.9%) if the time since the last vaccination dose was more than 6 month, and 44.8% (95% CI: 6.1–67.6%) if within 6 months. The heterologous booster vaccination adjusted VE (76%, 95% CI: 15–93%) was much better than that of the homologous booster vaccination (52%, 95% CI: 10–74%).
Table 4 shows the VEs of the inactivated vaccines against the Omicron variant infection. The estimated adjusted VE for a booster vaccination against infection was 48.0% (95% CI: 8.0–70.6%). Almost the same results were found for the VEs in the other subgroups.
Table 5 shows the VEs of the recombinant protein vaccine against the Omicron variant infection. Among these partial and full vaccination groups, partial vaccination showed no protection, and full vaccination was 12.1% (95% CI: −78.6–56.8%) effective against infection. Recombinant protein vaccine provided better protection for females (VE=16.8, 95% CI: −107–66.5%) than males (VE=3.5%, 95% CI: −199.8–68.9%). The adjusted VEs were similar in the two age groups. Any dose of recombinant protein vaccine offered 12.4% (95% CI: −77.8–56.8%) protection for infection after 6 months.
Table 6 shows the VEs of the Ad5-nCoV vaccine against Omicron variant infection. The overall adjusted VE of the Ad5-nCoV vaccine was 65.8% (95% CI: 12.8–86.6%). The estimated adjusted VE for booster vaccination against infection was 62.9% (95% CI: 1.8–86%). It also provided better protection for females (VE=88.3%, 49.4–97.3%) and individuals aged over 60 years (VE=62.7%, 95% CI: −15.1–87.9%) than the other two types of COVID-19 vaccines. The adjusted VE of the Ad5-nCoV vaccine was 62.9% (95% CI: 1.8–86.0%) within 6 months.