A third dose of the Sinovac vaccine gave older people a much higher level of protection against severe disease and death from Covid-19, according to a new study by scientists in Hong Kong.
The study shows that the current Omicron wave in Hong Kong is a cautionary note for mainland China, where Sinovac is a pillar of the country's vaccine program. There are many older people who haven't received booster shots.
The study found that two Sinovac doses were effective against Covid-related death for people 60 and older. The levels of protection were not as high as those provided by Pfizer-BioNTech. The study found that they were effective against death and Covid among Hong Kong residents of the same age group.
The study found that a Sinovac booster shot was 98 percent effective against severe or fatal Covid among people at least 60 years old.
The results highlighted the need for mainland China to accelerate its booster campaign, according to a global health expert.
The city's booster program began just recently, making it difficult to determine how long protection from a third dose would last.
They said that people with underlying health conditions in Hong Kong were more likely to resist getting vaccine and that it was possible that those who chose to be boosted were healthier in the first place.
Sinovac, a private Chinese company that makes the vaccine, is one of two manufacturers of Covid shots in China. Pfizer-BioNTech and Moderna's vaccines are not available there.
China is battling its biggest Covid outbreak in two years and has relied heavily on Sinovac. Almost all of China's population has beenvaccinated. Zeng Yixin, a vice minister of the National Health Commission, said recently that less than 20% of people in their 80s have received a booster.
There are many vaccines that have been tested in humans.
Pfizer's vaccine gave less protection against Covid than Sinovac's, but a booster dose lifted levels of protection. The subvariant of Omicron known as BA.2 has mostly affected people in Hong Kong. BA.2 has the same problem as other versions of Omicron.
The Hong Kong wave is killing people at a higher rate than any other country since the coronaviruses emerged, and it's partly due to low vaccination rates among older residents. Almost 90 percent of people who died during the latest wave were not fully immunized, suggesting that getting shots to the most vulnerable is more important than the particular brand of vaccine.
Like Hong Kong, mainland China's population has very little immunity to previous infections because of the suppression of transmission of the virus before Omicron.
Sinovac vaccines have been important in protecting people against Covid in poorer countries. In South America and Africa, the vaccine is being used.
The World Health Organization recommended in October that recipients 60 and older get a third dose because of concerns about the protection it offered.
Andrew Morris, an infectious disease specialist at Sinai Health and University Health Network in Toronto, who was not involved with the Hong Kong study, said that the results fit with lab studies suggesting that Sinovac generated lower levels of neutralizing antibodies than Pfizer's vaccine.
I think what we will see is in countries that have relied heavily on Sinovac, if they don't have boosting, especially with an mRNA booster.
The results of vaccine studies are highly dependent on how long people have been given the shots, according to Dr. Morris. Over time, protection tends to weaken.
The results from the latest study about the effectiveness of third Sinovac doses might be taken as an encouraging sign by Chinese leaders that Chinese-made vaccines could remain the focus of their immunization campaign.
He said that the Chinese leaders don't need to face a strong pressure to approve the vaccine.
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