Studies detail Omicron immune protection after infection, vaccination


Center for Infectious Disease Research and Policy

Mary Van Beusekom, MS

A pair of new studies describe infection- and vaccine-conferred immunity against the SARS-CoV-2 Omicron variant, with one showing that vaccinated people have good protection against BA.5 subvariant reinfection for at least 8 months after infection, and the other finding that the vaccine is 46% and 70% effective against infection and hospitalization, respectively, in children.

Hybrid immunity ‘quite stable’

Researchers in Portugal mined a national COVID-19 registry for data on more than 9.3 million vaccinated people 12 years or older from Jan 1 to Sep 14, 2022, a period of Omicron BA.1 and BA.2 predominance. The team compared previously infected people with their uninfected peers.

In Portugal, virtually all people had received a vaccine booster dose. The research was published yesterday in The Lancet Infectious Diseases.

The previously infected group initially was about 90% protected against reinfection, with protection falling to 70% after 5 months and then stabilizing at 65% at 8 months. Their relative risk, compared with that of COVID-naïve participants, was 0.24 initially and 0.32 at 3 months.

“These results show that hybrid immunity conferred by infection with previous subvariants of SARS-CoV-2 in vaccinated people is quite stable,” co-senior author Luis Graca, MD, PhD, of the University of Lisbon said in an Instituto de Medicina Molecular news release.

Protection highest after booster

In the second study, published yesterday in the Journal of Infection, Chinese researchers conducted a meta-analysis of 14 observational studies on COVID-19 vaccine effectiveness (VE) in children and adolescents. The studies, published from Nov 1, 2021, to Nov 30, 2022, included nearly 3.8 million children.

Pooled VE against Omicron infection in children was 46.3%, with a VE of 18% after the first dose and 50.7% after the second. Among adolescents, VE against infection was 54.4%, with 39.1% VE after the first dose, 60.6% after the second, and 63.4% after a booster. VE against hospitalization in both children and adolescents was about 70%.

VE against symptomatic COVID-19 was 45.2% in children and 73.1% in adolescents, with 26.4% VE after the first dose, 59.7% after the second, and 71.1% after a booster.