Hybrid Immunization Can Provide 90% Protection Against Omicron BA.5 Variant


Relative risk calculations show that vaccinated individuals infected with the first Omicron subvariants of COVID-19 could have protection that lasts nearly 3 seasons.

Hybrid immunity, which is conferred by a combination of vaccination and infection, may offer better protection against the Omicron BA.5 variant of COVID-19 than immunization alone, according to new research published in Lancet Infectious Diseases. Those who contracted previous subvariants of COVID-19 while vaccinated gained immunity that can extend to 8.5 months, according to the study.

“Protection conferred by vaccination together with previous infections is stable and maintained until at least 8 months after the first infection,” said the study’s first author, João Malato, in a press release.

The study authors previously researched the conferred protective benefits of infection from the first Omicron subvariants of SARS-CoV-2 (circulating in January and February 2022) with vaccination. Their findings showed that this hybrid immunity was effective against the BA.5 variant (in circulation in Portugal since June 2022). They published these findings in the New England Journal of Medicine in September 2022.

"In September, we had observed that infection by the first omicron subvariants conferred protection for the BA.5 subvariant about four times higher than vaccinated people who were not infected on any occasion, showing the importance of hybrid immunity for protection against new infections,” Graça said in the press release.

However, the investigators’ earlier research did not examine the stability of protection from hybrid immunity. In the current study, the team aimed to determine the longevity of these duel protective measures.

The Portugal-based researchers decided to use a national, comprehensive COVID-19 registry to collect data on all COVID-19 cases among those aged 12 years and older who live in Portugal. Because 98% of the population were vaccinated by 2021, it made it easier to gauge the efficacy of hybrid immunity against what was, at the time, the most recent strain of Omicron, according to study co-leader Manuel Carmo Comes, associate professor with aggregation at the Faculty of Sciences of the University of Lisbon.

Calculating the relative risk of reinfection among the hybrid-immunized population, the researchers discovered that hybrid immunity can offer prolonged protection against the omicron BA.5 variant.

“These results show that hybrid immunity conferred by infection with previous subvariants of SARS-CoV-2 in vaccinated people is quite stable", said study co-author Luís Graça, a group leader at the Instituto de Medicina Molecular João Lobo Antunes in Lisbon, Portugal, and full professor at the Medical School of the University of Lisbon, in the press release. “Protection is “maintained until at least 8 months after the first infection."

The data also showed that protection can hover at 90% for the 5 months following initial infection. After 5 months, relative protection was, “reduced to about 70% and show[ed] a tendency to stabilize at a value of around 65% after 8 months, compared to the protection in vaccinated persons that were never infected by the virus,” Graça said in the press release.


Instituto de Medicina Molecular. Vaccine and prior SARS-CoV-2 infection confer long-lasting protection against omicron BA.5. January 5, 2023. Accessed on January 6, 2023. https://www.eurekalert.org/news-releases/975533

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