COVID-19 infection comes with long-lasting immunity, however—immunity might vary depending on the emerging variant

Researchers from the Peter Doherty Institute for Infection and Immunity (Doherty Institute) have found that breakthrough SARS-CoV-2 infection in vaccinated individuals provides long-lasting immunity against similar strains of the virus. However, immunity from newer variants is significantly reduced.

A highly distinct variant of SARS-CoV-2, Omicron and its subvariants rapidly outcompeted the Delta variant to become the dominant strain in early 2022, driving increasing numbers of vaccine breakthrough infections worldwide. A study, published in Science Advances, shows that the high transmissibility and immune evasion capacity of Omicron along with the declining effectiveness of vaccine-elicited immunity have resulted in increasing frequencies of “breakthrough” infections of vaccinated individuals.

“SARS-CoV-2 is constantly evolving. It can change so much that, even if you’re vaccinated, when you catch COVID-19 for a second time, your immune system might no longer recognise the virus and protect you from infection,” said University of Melbourne’s Dr Wen Shi Lee, Post-Doctoral Researcher at the Doherty Institute and co-first author of the paper.

In a longitudinal study, Doherty Institute researchers from the University of Melbourne’s Department of Microbiology and Immunology, in collaboration with the Kirby Institute, investigated the immune response in vaccinated people who got infected with Omicron BA.1 or BA.2, by collecting blood and nasal swab samples up to eight months after the infection.

“We found that breakthrough infections led to increased activity in immune cells that remember both the ancestral variant of the virus and Omicron. But not many new cells that specifically target Omicron were created and when dealing with newer subvariants of the virus – XBB and BQ.1.1, the immune response wasn’t as strong,” said University of Melbourne Dr Hyon Xhi Tan, Post-Doctoral Researcher at the Doherty Institute and co-first author of the paper.

University of Melbourne’s Dr Adam Wheatley, Laboratory Head at the Doherty Institute and senior author on the paper, explained the impact of the findings.

“Our research suggests that after recovery from COVID-19, your antibodies are boosted and re-infection with closely related strains is much less likely. However, this protection could be undermined by emerging strains of the virus, which evade recognition by our antibodies and are therefore harder to neutralise,” said Dr Wheatley.

Repeated, successive waves of Omicron outbreaks have driven substantial breakthrough infections and seeded “hybrid” immunity (a combination of vaccination and infection) in much of the global population. Our data suggest that, in this context, the ongoing spread of SARS-CoV-2 will be influenced less by waning immunity and more by the virus acquiring additional mutations to escape neutralisation,” he added.

Understanding how periodic infection with increasingly distinct SARS-CoV-2 variants affects the lasting strength of the immune response is critical. This knowledge will inform the development of future COVID-19 vaccines to maximise the level of protection of the population against future variants.