Inactivated COVID-19 vaccines to make a global impact

The vaccine showed good safety and tolerability; adverse reactions, the most frequent being injection site pain (39 [9%] of 421 participants), were all mild or moderate in severity and no serious adverse events related to vaccination were recorded. Neutralising antibody titres were measured for all doses 28 days after the second injection. Because similar responses were seen with doses of 3 μg (seroconversion rate 98·0% [95% CI 92·8–99·8]) and 6 μg (99·0% [94·5–100·0]) in phase 2, and these doses elicited better responses than did the 1·5 μg dose, the authors proposed the use of a 3 μg dose in the phase 3 trial. Comparisons of various vaccine platforms have been hampered because, until recently, there were no standard pooled convalescent sera from infected individuals to use as a reference standard.6 Interpretation of immune responses is limited in that no consensus standard methods for measuring neutralising antibody titres are in place, thereby confounding comparisons between age groups and comparisons with different vaccine strategies.