A research team has found that the effectiveness of both the BioNTech and Sinovac vaccines in preventing Omicron infections drop substantially over 100 days after vaccination, although they can still prevent severe illnesses and death.

Releasing its findings on Tuesday, the research team said three and four doses of the BioNTech vaccine were 48 percent and 69 percent effective in preventing Omicron infections seven days after vaccination, but they waned to 26 and 35 percent respectively 100 days after the shot.

As for the Sinovac jab, researchers said while three and four doses were 30 and 56 percent effective after seven days, they drop to six and 11 percent by the 100th day.

The research was co-led by professors Joseph Wu and Malik Peiris from the University of Hong Kong’s School of Public Health.

Other team members include experts from the University of Hong Kong, the Chinese University, Washington University in the US, University of Melbourne in Australia, and Ishikawa Prefectural University in Japan.

The team said the findings were based on a community-wide serological survey of 5,310 blood donors and volunteers in Hong Kong, as well as analysis of the SAR government’s Covid-19 viral load data from wastewater surveillance.

It said the study is one of few that looked into how the vaccines can prevent the transmission of Omicron, although there is already extensive data showing vaccines can “robustly prevent severe disease, hospitalisation and death” after an infection.

“The results indicate that booster vaccination using either the mRNA or inactivated vaccine platforms is effective in preventing SARS-CoV-2 Omicron BA.2 infection in the short-term,” the team said in a statement.

“Thus, surge booster campaigns, particularly with updated bivalent mRNA vaccines, could be strategically used to rapidly boost population immunity when there’s risk of future waves of infection arising from a concerning novel virus variant.”