Omicron infection induces limited immune response in unvaccinated

Unvaccinated people infected with the Omicron variant are unlikely to develop immune responses that will protect them against other variants of the coronavirus, a new study suggests.

Unlike antibodies induced by COVID-19 vaccines or infections with earlier SARS-CoV-2 variants, antibodies induced by the Omicron BA.1 and BA.2 variants do not neutralize other versions of the virus, researchers found when they analyzed blood samples obtained after Omicron infection.

People with Omicron “breakthrough” infections after three doses of the mRNA vaccines designed to neutralize earlier versions of the virus had high levels of neutralizing antibodies against the two Omicron variants, although the efficiency was lower than against previous SARS-CoV-2 versions, according to a report undergoing peer review at Nature Portfolio and posted on Research Square.

But among those whose immune systems had not been primed to recognize the virus through vaccination or by natural infection, antibodies after Omicron infection “were very specific for the respective Omicron variant, and we detected almost no neutralizing antibodies targeting non-Omicron virus strains,” said Karin Stiasny and Judity Aberle of the Medical University of Vienna, Austria in a joint email.

BA.2-induced antibodies appeared to be particularly unlikely to defend against any other variant, they added. The study “emphasizes the importance of booster vaccinations for immune protection.”