Boosting immunity after CoronaVac

Adult study participants were recruited to include two equally sized age groups: younger than 60 years and 61 years and older. 1205 individuals, of whom 729 (60·5%) were women and 814 (67·6%) were White, were available for analysis of primary outcomes, which included reactogenicity and immunogenicity of IgG antibodies and neutralising activity before the boost and 28 days after.5 Three serious adverse events possibly related to the vaccine occurred, which resolved completely. Across all vaccines, responses after boosting were lower in the older age group than in the younger group.5 Although the COV-BOOST study with different vaccine combinations has shown a similar advantage of mRNA and vector vaccines over adjuvanted protein-based vaccines,7 the rapidly spreading omicron variant underscores the need for large cohort studies to determine whether the differences in immunogenicity after booster vaccination observed with age and vaccine regimens will correlate with different susceptibility towards infection or disease. Additionally, with increasing immune escape, there is a need for diagnostic assays adapted to characterise vaccine-induced humoral and cellular immunity towards specific SARS-CoV-2 variants, which should also include determination of meaningful correlates for protection.8,9 Of note, the present study did not assess T-cell immunity, which could inform on the ability to protect from severe disease and which was shown to be markedly induced after heterologous vector or mRNA vaccination in healthy and immunocompromised individuals.3,10 Among approximately 10 billion vaccine doses administered globally, CoronaVac accounts for more than 2 billion doses, making it the world's most frequently used SARS-CoV-2 vaccine.11 It is noteworthy to mention that there are considerable price differences between the SARS-CoV-2 vaccines, which could influence the choice of booster vaccines in low-income and middle-income countries.