SHANGHAI (BLOOMBERG) - A longer gap between second and third doses of China's Sinovac Covid-19 vaccine provides more protection against the virus than a shorter wait, according to a study published in medical journal The Lancet.
Antibody levels in people who received a third dose eight months after their second dose rose more than twice as much as people who got a booster shot within two months of their second dose, according to researchers from Sinovac Biotech, Fudan University and several regional Centres for Disease Control and Prevention.
The study found that while protection from Covid-19 six months after two doses of the vaccine, also known as CoronaVac, had "declined substantially", a third dose at eight months resulted in a "remarkable increase" in the concentration of antibodies.
The findings come as countries around the world accelerate drives to distribute booster shots as they grapple with the new, more transmissible Omicron variant.
While some places such as South Korea are cutting booster timelines to just three months after the second shot - a strategy endorsed by BioNTech chief executive Ugur Sahin - the Lancet study suggests that rushing the third dose may not be the best approach for those on inactivated vaccines like Sinovac.
The Beijing-based company's shot is the most widely used globally with 2.3 billion doses shipped out, mostly around the developing world.
While still highly effective at warding off serious illness and death, it protects much less against transmission and symptomatic disease than the mRNA vaccines for the original strain of the virus and the Delta variant.
Sinovac is studying how the vaccine holds up against Omicron.
Around 38 million people have received a booster shot in China, Dr Wang Huaqing, chief immunisation expert at the Chinese Centre for Disease Control and Prevention, said at a briefing in November.
Hong Kong also started to roll out booster shots on Nov 11 with high-risk groups who received the Sinovac vaccine. The study, published on Dec 7, also suggests that people aged 60 years or older received higher antibody concentration from a third shot than 18- to 59-year-olds.
