Experts who advise the government on Covid-19 and vaccines on Friday recommended adults between the age of 18 and 59 to consider getting a fourth vaccine dose if they have never been infected.

The "interim recommendations" came a day after the joint-scientific committees under the Centre for Health Protection and the chief executive's expert advisory panel discussed the matter.

The advisers said although three doses of BioNTech or Sinovac are highly effective in warding off serious illnesses or death, the level of protection wanes after several months.

"A fourth dose of Covid-19 vaccine in younger populations may provide transient additional protection against infection and symptomatic diseases," they said in a document published on the Centre for Health Protection’s website.

The experts pointed out that those who are at a higher risk of Covid-19 exposure or have personal needs, such as to study abroad or to fulfill a requirement of overseas travel, may choose to get the fourth jab at least six months after receiving the third dose.

People who are aged 60 or above are already recommended to get a fourth shot.