An elderly woman receives COVID-19 vaccine in April in Shanghai. Photo: VCG

A recent study showed that vaccinated individuals can develop more robust and broadly reactive antibody responses against COVID-19 variants than the unvaccinated after an Omicron infection, which underlines the importance of COVID-19 vaccination even for people who have already been infected and for the elderly who might be exposed to infection in the future.

The study was jointly conducted by researchers from the University of Hong Kong and the Chinese University of Hong Kong and published on the medical journal Eurosurveillance in May.  

The study compared the neutralizing antibodies to COVID-19 variants, including Omicron subvariants BA.1 and BA.2, the wild-type virus, Delta and Beta in vaccinated and non-vaccinated people who have all been infected by Omicron. 

The findings show that an Omicron infection in unvaccinated people can only induce very weak antibody responses which can react against Omicron only. By contrast, an Omicron infection in fully vaccinated individuals leads to a more potent antibody response, which is six times higher than those of unvaccinated COVID-19 patients, and the antibodies can also react against other variants, such as Beta and Delta.

"The findings of the study mean that those who had not been vaccinated and only got infected do not have a strong and broad immunity, so they should get fully vaccinated as soon as possible. Ideally around 3 months after full recovery," Malik Peiris, professor in School of Public Health of Li Ka Shing Faculty of Medicine in the University of Hong Kong who led the study, told the Global Times on Tuesday.  

Malik Peiris also emphasized the necessity for the elderly to get vaccinated, saying that there are still a few hundred thousand people over the age of 70 or 80 years in Hong Kong who have not got vaccinated but really need to get vaccinated a soon as possible. 

"The elderly people cannot assume they will not be exposed to infection sometime in the future as we know that COVID-19 infection in the elderly can be very serious and even fatal. This is completely preventable because we have good, safe and effective vaccines which are completely safe even in the elderly," said Malik Peiris.