Two doses and a booster of Sinovac fail to protect against Omicron: Study

Two doses and a booster of the Covid-19 vaccine made by China’s Sinovac Biotech Ltd., one of the most widely used in the world, didn’t produce sufficient levels of neutralizing antibodies to protect against the omicron variant, a laboratory study found.  

The research suggests that people who’ve received Sinovac’s shot, known as CoronaVac, should seek out a different vaccine for their booster: Getting Germany’s BioNTech SE’s messenger RNA as a third dose saw those previously fully vaccinated with CoronaVac significantly improve in protective levels of antibodies against omicron, according to the study from the University of Hong Kong and The Chinese University of Hong Kong. 

Two doses of the BioNTech shot, known as Comirnaty, was also insufficient, though adding a booster of the same type raised protection to adequate levels, the researchers said in a statement. 

While much is still unknown about how Sinovac’s shot holds up to omicron -- including how T cells, the immune system’s weapon against virus-infected cells, will respond -- the initial results are a blow to those who have received CoronaVac. There have been more than 2.3 billion doses of the shot produced and shipped out, mostly in China and the developing world. 

With omicron seen to be about 70 times more transmissible than the delta variant, the prospect of having to roll out different boosters or even re-vaccinate with a more omicron-specific vaccine will set back the world’s efforts to exit the pandemic.

Last week, Sinovac released lab studies saying 94% of people getting three doses generated neutralizing antibodies, though it didn’t say what level. The Hong Kong researchers set a threshold for what they considered a sufficient level of antibodies for protection based on earlier studies published in the journal Nature Medicine. 

Sinovac representatives didn’t immediately respond to calls seeking comment. 

The research, led by Malik Peiris and David Hui, examined the production of virus neutralizing antibodies in the blood of people vaccinated with the two shots currently in use in Hong Kong. They confirm two doses of either vaccine wasn’t sufficient to fend off omicron. 

The news comes as Hong Kong’s medical advisers cleared the way for adults in the city to receive a booster shot, no matter which vaccine they initially received. The new study suggests there are critical differences between them. 

The findings are bad news for China, which has managed to insulate the vast majority of its people from Covid-19 with closed borders and strict containment measures, but now faces the challenge of keeping omicron out. The government has given out 2.6 billion homegrown shots -- many of them CoronaVac -- to its population of 1.4 billion people, but will likely have to develop and roll out new vaccines before it can shift away from its isolationist stance.