New research has found that those who have been vaccinated and then catch COVID will produce a longer lasting and stronger antibody response, which is not restricted to the specific strain of the virus.

The study jointly conducted by the LKS Faculty of Medicine, The University of Hong Kong (HKUMed) and the Faculty of Medicine, The Chinese University of Hong Kong (CU Medicine) found that vaccinated individuals can develop more robust and broadly reactive antibody responses against SARS-CoV-2 variants than unvaccinated individuals after an Omicron infection.

The team said the results further highlight the need for COVID-19 vaccination for unvaccinated people even after a SARS-CoV-2 infection.

The team undertook the study as variant of concern (VOC) Omicron, caused the fifth COVID-19 wave in Hong Kong.

“This virus acquired novel mutations in its spike protein and allowed vaccine breakthrough infection,” the study explained. The research led by Professor Malik Peiris, Tam Wah-Ching professor in Medical Science and chair professor of Virology at the School of Public Health, HKUMed and professor David Hui Shu-cheong, Stanley Ho professor of Respiratory Medicine and chairman of Department of Medicine and Therapeutics, CU Medicine, studied the virus neutralising activity in the blood of vaccinated individuals after an Omicron, BA.1 or BA.2, infection.

The found that an Omicron infection in unvaccinated people can only induce very weak antibody responses, which react with Omicron only. In contrast, a breakthrough infection caused by Omicron in fully vaccinated individuals leads to a more potent antibody response, which is six times higher than those of unvaccinated COVID-19 patients. More importantly, such an antibody response found in vaccinated individuals is broadly reactive and it can react with other VOCs, such as Beta and Delta.

“Vaccination can help do more other than preventing severe COVID-19 outcomes,” Peiris explained. “Those who had been fully vaccinated with either BNT162b2 or CoronaVac and then got breakthrough infection have very strong and very broad immunity against many variants including BA.2, BA.1 and others. Thus, for vaccinated individuals, the infection can help to train your body to better prepare for a re-infection caused by another SARS-CoV-2 variants in future.”

Hui added: “Do not assume an Omicron infection in unvaccinated individuals alone can induce strong immunity to protect yourself against future variants. Antibody response induced by a natural infection with Omicron in unvaccinated people is weak and not broadly reactive to other VOCs. These patients are highly recommended to get vaccinated after full recovery from infection (at least one month or more after the infection).”

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