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BA.2 Less Likely to Escape Immunity Than Original Omicron Variant

Immune escape for the BA.2 subvariant, or “stealth Omicron,” was not as severe as that of the original Omicron variant, a new study suggests.


The BA.2 Omicron subvariant of the SARS-CoV-2 virus may be slightly more susceptible to current vaccines and antibodies triggered by prior infection than the earlier BA.1 Omicron subvariant, new research by investigators in China suggests.

The study, highlighted in a correspondence in The Lancet Microbe, measured serum neutralizing antibody activity against both subvariants among patients who had prior exposure and/or vaccination.

“Our study indicates that Omicron sublineage BA.2 is slightly more susceptible to neutralizing antibody elicited by prior infection with or without vaccination than BA.1, while there is no significant difference between BA.2 and BA.1 for individuals with 3 doses,” corresponding author Kelvin Kai-Wang To, MD, of the State Key Laboratory for Emerging Infectious Diseases at The University of Hong Kong told Contagion. “Our result is consistent with a study in Qatar, which showed a slightly higher vaccine effectiveness against BA.2 than BA.1 (51.7% for BA.2 vs 46.6 for BA.1).”

Overall, the study found the geometric mean neutralizing antibody titer (GMT) was 1.68 times greater against the BA.2 subvariant than the original Omicron variant (73.2 vs 43.7; p<0 0001).

The study evaluated antibody activity against BA.2 compared with BA.1 among subgroups including those who had one dose of vaccine after a COVID-19 infection in 2020, those who had COVID-19 in 2020 but no vaccine and those recently infected with the BA.2 subvariant. GMT was higher against the BA.2 subvariant by 2 times, 2.3 times and 2 times respectively. There was no statistically significant difference among participants who received three doses of COVID-19 vaccine.

“Since NAb titres correlate with vaccine effectiveness, our data suggest that currently available vaccines might be more effective against BA.2 than BA.1,” the authors wrote.

The BA.2 subvariant appears to be up to 60% more transmissible than the original Omicron subvariant, raising concerns among health experts that the subvariant could bring a new surge of cases. It was detected in the United States in January and has gradually been overtaking the original Omicron variant.

“We initially conducted the study because Hong Kong is one of the earliest places severely affected by BA.2,” To said. “At that time, there were only reports on BA.1 but not BA.2. It’s reassuring that BA.2 is not more resistant to neutralizing antibodies than BA.1.”

He said clinicians and healthcare workers should be aware that three doses of current COVID-19 vaccines elicit neutralizing antibody activity against BA.2 in most individuals. Those who have had prior infection also could benefit from much higher antibody levels from vaccination than from prior infection alone.

“The next step will be to continuously monitor the neutralization susceptibility for upcoming variants,” To said.

Health officials have kept a watchful eye on vaccine effectiveness. Previous research showed that primary vaccination was less effective against the Omicron variant than the prior Delta variant. Vaccine manufacturers have been weighing investigational vaccine formulas to target variants.