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Published: 11:45, October 28, 2021 | Updated: 12:54, October 28, 2021
Hong Kong experts back COVID-19 booster jab for elderly and high-risk
By Wang Zhan
Published:11:45, October 28, 2021 Updated:12:54, October 28, 2021 By Wang Zhan

A nurse fills a syringe with a dose of the Sinovac Biotech Ltd’s COVID-19 vaccine at a community vaccination center in Hong Kong, on Feb 26, 2021. (BILLY HC KWOK/GETTY IMAGES VIA BLOOMBERG)

HONG KONG – Government health advisers have recommended that immunocompromised individuals and high-risk groups in Hong Kong should be given top priority to receive a COVID-19 vaccine booster dose

The two scientific committees under the Centre for Health Protection met on Wednesday to review 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,” Prof David Hui, chairman of Scientific Committee on Emerging & Zoonotic Diseases, said at a media session after the meeting.

“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.

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

Prof David Hui, Chairman, Scientific Committee on Emerging & Zoonotic Diseases

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 advised 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 person has already received two doses of the BioNTech vaccine, there is no reason for them to switch to a weaker immunogenic agent, he said, adding that 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.

EXTRA DOSES

The recommendations pave the way for extra doses to be administered in Hong Kong, amid research being conducted across the world that suggests the efficacy of all the vaccines declines over time. Israel has administered millions of booster shots and is making preparations in case a fourth round is needed. The US and UK, meanwhile, started offering the extra shots widely last month, while Europe has endorsed third doses. 

The Chinese mainland recently approved and began to roll out boosters for high-risk residents. The World Health Organization’s advisory group also recommended people aged 60 and older who received Sinovac and Sinopharm vaccines get a third dose.

Some experts have questioned the need for the broad use of boosters, as existing vaccines reduce the risk of serious disease and death. The WHO called for a moratorium on them for most people this year, until the available vaccines are more widely distributed and poorer nations have better access.

Hong Kong has received Sinovac’s application to lower the age limit for innoculations to three, down from 18 years old, but the advisers said they haven’t made a decision yet. Currently, children aged 12 to 17 are allowed to receive shots made by BioNTech.

Among the 4.6 million people who have received at least one dose, about a third opted for Sinovac and two-thirds chose BioNTech. The city also procured 7.5 million shots from AstraZeneca, but plans to donate it all to COVAX, a global vaccine program designed to help developing and middle-income countries get the inoculations.

With inputs from Bloomberg

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