Neutralizing antibodies against the SARS-CoV-2 Omicron variant BA.1 following homologous and heterologous CoronaVac or BNT162b2 vaccination

Serum neutralizing antibody titers against the SARS-CoV-2 Omicron variant markedly increase after a third dose of BNT162b2 vaccine in individuals who previously received either two doses of the BNT162b2 vaccine or two doses of the CoronaVac vaccine. The Omicron variant is rapidly becoming the dominant SARS-CoV-2 virus circulating globally. It is important to define reductions in virus neutralizing activity in the serum of convalescent or vaccinated individuals to understand potential loss of protection against infection by Omicron. We previously established that a 50% plaque reduction neutralization antibody titer (PRNT50) >= 25.6 in our live virus assay corresponded to the threshold for 50% protection from infection against wild-type (WT) SARS-CoV-2. Here we show markedly reduced serum antibody titers against the Omicron variant (geometric mean titer (GMT) < 10) compared to WT virus 3-5 weeks after two doses of BNT162b2 (GMT = 218.8) or CoronaVac vaccine (GMT = 32.5). A BNT162b2 booster dose elicited Omicron PRNT50 titers >= 25.6 in 88% of individuals (22 of 25) who previously received 2 doses of BNT162b2 and 80% of individuals (24 of 30) who previously received CoronaVac. However, few (3%) previously infected individuals (1 of 30) or those vaccinated with three doses of CoronaVac (1 of 30) met this threshold. Our findings suggest that countries primarily using CoronaVac vaccines should consider messenger RNA vaccine boosters in response to the spread of Omicron. Studies evaluating the effectiveness of different vaccines against the Omicron variant are urgently needed.

Automated summary

Specific antibody levels against the SARS-CoV-2 Omicron variant decrease significantly after two doses of BNT162b2 or CoronaVac vaccines, but can be markedly increased with a booster dose of BNT162b2. Individuals who previously received two doses of BNT162b2 or CoronaVac showed reduced serum antibody titers against Omicron, while a BNT162b2 booster dose increased the antibody levels in the majority of individuals. This suggests mRNA vaccine boosters may be necessary in countries primarily using CoronaVac vaccines to combat the spread of Omicron.