SARS-CoV-2 Omicron variant BA. 2 neutralisation in sera of people with Comirnaty or CoronaVac vaccination, infection or breakthrough infection, Hong Kong, 2020 to 2022

Background: Omicron subvariant BA.2 circulation is rapidly increasing globally. Aim: We evaluated the neutralising antibody response from vaccination or prior SARS-CoV-2 infection against symptomatic infection by BA.2 or other variants. Methods: Using 50% plaque reduction neutralisation tests (PRNT50), we assessed neutralising antibody titres to BA. 2, wild type (WT) SARS- CoV-2 and other variants in Comirnaty or CoronaVac vaccinees, with or without prior WT-SARS-CoV-2 infection. Titres were also measured for non- vaccinees convalescing from a WT-SARS- CoV-2 infection. Neutralising antibodies in BA.2 and BA.1 breakthrough infections and in BA. 2 infections affecting non- vaccinees were additionally studied. Results: In vaccinees or prior WT-SARS-CoV-2-infected people, BA.2 and BA.1 PRNT 50 titres were comparable but significantly (p < 10(-5)) lower than WT. In each group of 20 vaccinees with (i) three-doses of Comirnaty, (ii) two CoronaVac followed by one Comirnaty dose, or (iii) one dose of either vaccine after a WT-SARS-CoV-2 infection, = 19 individuals developed detectable (PRNT50 titre <= 10) antibodies to BA.2, while only 15 of 20 vaccinated with three doses of CoronaVac did. Comirnaty vaccination elicited higher titres to BA.2 than CoronaVac. In people convalescing from a WT-SARS-CoV-2 infection, a single vaccine dose induced higher BA.2 titres than three Comirnaty (p = 0.02) or CoronaVac (p = 0.00001) doses in infection-naive individuals. BA.2 infections in previously uninfected and unvaccinated individuals elicited low (PRNT50 titre <= 80) responses with little cross-neutralisation of other variants. However, vaccinees with BA.1 or BA.2 breakthrough infections had broad cross- neutralising antibodies to WT viruses, and BA.1, BA.2, Beta and Delta variants. Conclusions: Existing vaccines can be of help against the BA.2 subvariant.

Automated summary

The study found that in vaccinees or prior WT-SARS-CoV-2-infected individuals, PRNT 50 titres for BA.2 and BA.1 were comparable but significantly lower than for the wild type virus. Vaccination with Comirnaty resulted in higher BA.2 titres compared to CoronaVac, while convalescents from a WT-SARS-CoV-2 infection had higher BA.2 titres after a single vaccine dose than after three doses of Comirnaty or CoronaVac in infection-naive individuals.