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KEY POINTS
- Study in China found that SinoVac and SinoPharm were 70% effective in preventing COVID-19 infection
- Preprint study in Brazil found that SinoVac was only 54% effective in preventing coronavirus infection
- Singapore had previously refused to count SinoVac injections in the country’s immunization tally
The Chinese-made COVID-19 vaccine, SinoVac, was found to produce significantly lower antibody levels than the vaccine developed by Pfizer-BioNTech, prompting residents of Singapore to receive booster shots.
Antibody levels in people who received two doses of Pfizer vaccine were normally between 1300 and 2000 international units per milliliter. However, the numbers are much lower in people who have received two injections of the SinoVac vaccine.
“For Sinovac, it’s zero to 40. We have a few with 200 to 300,” Dr. Leong Hoe Nam, infectious disease specialist at the Rophi Clinic in Singapore, told the South China Morning Post.
Dr Leong noted that the lower antibody levels in SinoVac recipients have prompted an increasing number of people to be given Pfizer as a booster shot.
“They took the Sinovac injections, had the blood test done and found low levels of antibodies, then switched to Pfizer as the third dose,” he added.
A study conducted by researchers in China found that the SinoVac and SinoPharm vaccines had a combined 70% effectiveness in preventing an infection caused by the more contagious Delta variant in the city of Guangzhou. The study, which has yet to be peer reviewed, also noted that the injections were 100% effective in preventing serious infections and death.
However, a Brazilian preprint study comparing SinoVac to the AstraZeneca COVID-19 vaccine found that recipients of the vaccine made in China had lower levels of protection against the virus.
SinoVac recipients were 54% less likely to contract COVID-19 and 74% less likely to die from the virus compared to unvaccinated ones. Efficacy declined in the older population, reducing the risk of death by only 35% in people over 80 years old. In comparison, AstraZeneca reduced the risk of infection by 70% and the risk of death by 90%.
The Singaporean government previously excluded people who received SinoVac vaccines from the country’s total number of vaccinations. Health Minister Ong Ye Kung cited inadequate efficacy data as the reason for the move.
“We don’t really have a medical or scientific basis or the data necessary to establish the effectiveness of SinoVac in terms of infection and serious illnesses on Delta,” Ong said at a press briefing in July, according to Reuters.
Singapore’s health ministry later announced that it would consider people who have received vaccines included in the World Health Organization’s emergency use list, such as SinoVac, Sinopharm, and AstraZeneca, to be fully vaccinated, in order to be more “inclusive”.
“What is important now is the difference between those who are vaccinated and unvaccinated and less between the different vaccines,” Ong said at a press conference in early August.
Despite this, the Singaporean government is still offering third doses of vaccine to residents who had taken the SinoVac vaccine as part of a “heterologous vaccination strategy”.
“We haven’t stopped them although the data is still lacking given the effectiveness of this strategy using two different vaccines – we call it a heterologous vaccination strategy,” Chief Medical Officer Kenneth Mak said during a virtual interview.
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