Virus neutralization of SARS-CoV-2 Omicron variant BA.2 in those vaccinated with three doses of BNT162b2 or CoronaVac vaccines. (preprint)

SARS-CoV-2 Omicron subvariant BA.2 is increasing in some areas of the world and it is important to assess how well current vaccines may protect against this infection. BioNTech Pfizer (BNT162b2) and CoronaVac are widely used COVID-19 vaccines globally. We determined the 50% plaque reduction neutralization test (PRNT50) and PRNT90 antibody titres to BA.2 virus in sera (twenty each collected 3-5 weeks after third dose) from cohorts vaccinated with three doses of BNT162b2, three doses of CoronaVac, two doses of CoronaVac followed by a third dose of BNT162b2 and those convalescent from SARS-CoV-2 (ancestral virus) (143-196 days after infection). We compared the PRNT titres to BA.2 with titres to BA.1 and ancestral virus. We demonstrate that PRNT50 and PRNT90 antibody titres to BA.2 are markedly reduced compared with those to ancestral virus and reduced as much as was observed for BA.1 virus. Those vaccinated with three doses of BNT162b2 or vaccinated with two doses of CoronaVac and a third dose of BNT162b2 develop PRNT antibody titres above the protective threshold from symptomatic infection. Those vaccinated with three doses of CoronaVac fail to achieve protective levels of PRNT50 antibody to BA.2 subvariant of Omicron 3-5 weeks after vaccination.

Neutralizing antibody titres to SARS-CoV-2 Omicron variant and wild-type virus in those with past infection or vaccinated or boosted with mRNA BNT162b2 or inactivated CoronaVac vaccines (preprint)

Omicron, a novel SARS-CoV-2 variant has emerged and is rapidly becoming the dominant SARS-CoV-2 virus circulating globally. It is important to define reductions in virus neutralizing activity in serum of convalescent or vaccinated individuals to understand potential loss of protection from infection or re-infection. Two doses of BNT162b2 or CoronaVac vaccines provided little 50% plaque reduction neutralization test (PRNT 50 ) antibody immunity against the Omicron variant, even at one-month post vaccination. Booster doses with BNT162b2 in those with two doses of either BNT162b2 or CoronaVac provided acceptable neutralizing immunity against Omicron variant at 1-month post-booster dose. However, three doses of BNT162b2 elicited higher levels of PRNT 50 antibody to Omicron variant suggesting longer duration of protection. Convalescent from SARS-CoV-2 infection did not have protective PRNT 50 antibody levels to Omicron, but a single dose of BNT162b2 vaccine provided protective immunity. Field vaccine-efficacy studies against Omicron variant against different vaccines are urgently needed.