Chinese drug maker Sinovac’s CoronaVac shot reduces the risk of symptomatic Covid-19 infections by half, in line with previous data, according to the long-awaited results of a phase three clinical trial in Brazil.
The trial by Brazil’s state-owned research institute Butantan involved 9,823 health care workers, who received two doses of the vaccine. The primary efficacy against symptomatic Covid-19 infection was 50.7 per cent, according to the study, which was published on Sunday but has not yet been peer reviewed.
“This pivotal trial for CoronaVac was able to demonstrate the safety and efficacy of a new Covid-19 vaccine,” the study said.
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The efficacy rate of the Sinovac inactivated vaccine, which uses dead material from the virus to trigger an immune response, is lower than mRNA vaccines from Western drug makers such as BioNTech-Pfizer and Moderna, whose products have been shown to be over 90 per cent effective.
mRNA vaccines are created by genetic engineering and instruct human cells to make the spike protein of the coronavirus so that the immune system will recognise and protect against it.
While 50 per cent is the threshold for regulatory approval of vaccines, the lower efficacy of the Chinese products, including one made by Sinopharm, whose inactivated shot is 79 per cent effective, has raised questions over whether they will be able to curb the spread of Covid-19.
Gao Fu, the director of the Chinese Centre for Disease Control and Prevention, said on Saturday that the authorities were considering two options to “solve the problem” of low efficacy: adjusting dosages and mixing different products.
However, in an interview with state-backed tabloid Global Times on Sunday, Gao said his remarks – made at a health conference – had been misunderstood. How to improve the efficacy of vaccines was something that needed to be considered by scientists around the world, he said.
In a positive development for Sinovac, a separate study in Brazil found its product to be almost 50 per cent effective at curbing the infection risk of the P1 Covid-19 variant that was first identified in the South American country.
The research, which was published on Wednesday but has not yet been peer reviewed, involved more than 46,800 health care workers in the city of Manaus, where the spread of the P1 variant has been rampant. Participants received at least one dose, which reduced the risk of symptomatic infection in the subsequent two weeks by 49.6 per cent, according to the study.
There have been concerns over the spread of variants. Some studies have found the Brazil variant could be up to twice as transmissible and immunity from a previous infection of an earlier strain of the coronavirus may not protect against it.
“Administration of at least one dose of CoronaVac showed effectiveness against symptomatic infection in the setting of epidemic P1 transmission, underscoring the need to increase vaccination efforts in response to the spread of this variant in Brazil and globally,” the study said.
Akiko Iwasaki, a professor of immunology at Yale University, said the study’s findings were promising.
“Good news is that CoronaVac, even after one dose, is able to reduce symptomatic infection significantly in a region of Brazil where P1 dominates,” she said on Twitter on Sunday.
“These early findings provide good support to securing vaccine supply and ramping up vaccination. This needs to happen as soon as possible to combat the devastating crisis in Brazil – where P1 has spread throughout the country.”
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