The two scientific committees under the Centre for Health Protection met today and recommended that immunocompromised individuals and high-risk groups should be given top priority to receive a COVID-19 vaccine booster dose.

Speaking at a media session after the meeting, Scientific Committee on Emerging & Zoonotic Diseases Chairman Prof David Hui said the recommendations were made after reviewing the latest scientific evidence and recommendations by the World Health Organization and overseas health authorities.

“The antibody level of those who have received an inactivated whole virus vaccine will decrease over time. So over about six to eight months it will drop to a quite low level and probably not be protective.

“So for the high risk group, if they have received the vaccine before and they have the antibodies drop to a low level, they will be at risk. That is why we have to have a list of immunocompromised individuals who are given top priority to receive the booster dose.”

The committees also recommended an additional COVID-19 vaccine dose for those who had received two doses of the Sinovac jab, in particular people with a higher risk of infection.

They include seniors aged 60 or above, healthcare workers, workers at increased risk for COVID-19 exposure and transmission such as those participating in anti-epidemic related work, providing cross-boundary transport or working at control points and ports and people with chronic illnesses.

Prof Hui added that people who had received two doses of the Sinovac jab may consider switching to the BioNTech one for a better immune response - a theory supported by an observational study published by a group in Turkey.

“For the mix and match vaccine, you all know that the mRNA (messenger ribonucleic acid) vaccine is actually stronger in stimulating the immune system, giving a higher antibody level. And the antibody level also tends to last longer.

“If the subject has already received two doses of the BioNTech vaccine, there is no reason for them to switch to a weaker immunogenic agent. There is no good scientific reason for them to do that.

“On the other hand, for those who have received two doses of CoronaVac vaccine which is a weaker immunogenic vaccine, if they switch to the BioNTech vaccine, that will actually stimulate a higher antibody level.”

For individuals in higher risk populations who had received two doses of the BioNTech vaccine, the committees also recommended that they get an additional dose of the BioNTech jab administered at least six months from the second dose.

The committees also discussed the co-administration of COVID-19 vaccines with inactivated seasonal influenza vaccines. Given the local context, they suggested maintaining the minimal interval of at least 14 days.