“For now, we know that a booster dose is needed… (and) we conduct studies from time to time as new scientific data emerges,” he said on Twitter.

“Importantly, our responses follow the new data. This is what is meant by an evidence-based response.”

Khairy had said yesterday that the ministry was conducting its own study after a foreign study found that Sinovac’s two-dose regime followed by a Pfizer booster was less effective against the Omicron variant.

His announcement was widely criticised by netizens.

One Twitter user tagged Khairy and the ministry after sharing a news article on the need for a fourth injection against Covid-19.

“This is why people don’t trust vaccines any more,” said the Twitter user.

In his reply to the Twitter user today, Khairy said variants such as Delta or Omicron did not exist when Covid-19 vaccines were developed.

He also noted how when Covid-19 was first detected, it was known as a “novel”, or new, coronavirus — which would inevitably go through mutations.

He added that the ministry’s response to the virus needed to change as it gained more understanding about the mutations.

A total of 6,329,155 booster doses have been administered in the country as of yesterday.

On Friday, a study by researchers at Yale University, the Dominican Republic’s health ministry and other institutions revealed that Sinovac’s two-dose vaccine, followed by a booster Pfizer shot, showed a lower immunity response against the Omicron variant compared to other strains.

According to the study cited by Reuters, two doses of the primary Sinovac vaccine and a Pfizer booster shot produced an antibody response similar to a two-dose mRNA vaccine.