Several countries in Southeast Asia are expected to implant the Chinese Sinovac vaccine, despite concerns about its effectiveness.
Data released from a Sinovac trial in Brazil this week suggested that its effectiveness was 50.4% – lower than previously thought and just slightly above the requirement set by the World Health Organization.
Indonesia ordered 125 million doses of Sinovac and began its vaccination campaign with President Joko Widodo, receiving a live injection on television.
The Philippines signed an agreement for 25 million doses, while Myanmar was promised a vaccine donation from China. Thailand, whose biggest supplier is AstraZeneca, has ordered 2 million doses of Sinovac and expects to start administering the first batch next month.
Elsewhere, Turkey began administering the Sinovac vaccine to health professionals on Thursday, after approving it for emergency use.
Health experts fear that public confidence has been eroded by a series of conflicting findings about effectiveness and say the lack of data is making it difficult to understand how the vaccine works.
Turkish researchers reported that it was 91.25% effective, an Indonesian trial reported 65.3%, while Brazilian research teams said last week that it was 78% effective in preventing mild to severe cases of Covid, only to clarify later that this was only a partial picture. On Tuesday, it was announced that the effectiveness was 50.4% for all symptomatic infections, including very mild infections, where people did not need clinical assistance.
Filipino President Rodrigo Duterte has since defended the Sinovac jab, saying it is “as good as any other vaccine invented by Americans or Europeans”. He said on Thursday that there was a race for vaccines and “rich countries bought all supplies”.
There are several possible reasons why the results vary so widely, including the size of the trials, the composition of the participants and the duration of post-vaccination observation. Brazil’s test was by far the largest, with 13,000 participants. However, it recruited only health professionals, who may be more alert to any symptoms and more exposed to the virus than others.
Lorenz von Seidlein, associate professor at the tropical medicine research unit at Mahidol University in Thailand, said the decision to disclose the findings to certain subgroups also distorted the findings. “The more you cut [findings] divided into smaller groups, the power of the study is reduced and therefore increases the chance that it is a spurious finding, ”he said.
The discovery of 100% protection against serious diseases in the Brazilian study was not statistically significant, he added – a point that would be taken advantage of if the provisional results were subjected to peer review.
The Sinovac do Brasil study is not the only case in which the subgroup analysis was offered. The vaccine developed by Oxford University and AstraZeneca also reported two different success rates. It showed 62% effectiveness when two full doses were administered to adults of all ages, and 90% in a subgroup of participants under 55 who received half a dose followed by a booster.
Sinovac was criticized for providing less data than Western vaccine manufacturers. The company said that not all tests were designed in the same way, but illustrated that the vaccine is safe and effective.
Dr. Thiravat Hemachudha, head of the Thai Red Cross Emerging Infectious Diseases Health Sciences Center, said it was possible that variants of the virus could also affect the results. “We can’t look at the data and see just the numbers,” he said. “In Brazil, the variant may be different from the variant in the USA or England.”
The Thai government, which reintroduced restrictions after a new wave of cases emerged last month, said it was asking Sinovac for more information after the Brazil report, but has not changed its plans.
Malaysia, where many areas are again blocked due to the increase in cases, also analyzed the Sinovac vaccine, but said it would review the company’s clinical data before proceeding.
Indonesia, which recorded nearly 25,000 deaths, started vaccinating health workers this week. “We are not waiting for a better vaccine because we don’t know when it will arrive in Indonesia,” said Covid vaccination spokeswoman for the health ministry, Dr. Siti Nadia Tarmizi. She said postponing more could increase the number of deaths.