Several countries in Southeast Asia are expected to use the Chinese Sinovac vaccine, despite concerns about its effectiveness.
Data released in a trial of the Sinovac jab in Brazil this week indicates that its effectiveness is 50.4% – lower than previously thought and just above the requirements set by the World Health Organization.
Indonesia ordered 125 million doses of Sinovac and began its vaccination campaign with President Joko Widodo, who was hit live on television.
The Philippines has signed an agreement for 25 million doses, while Myanmar has been promised a vaccine donation by China. Thailand, whose largest supplier is AstraZeneca, has ordered 2 million doses of Sinovac and hopes to start administering the first batch next month.
Elsewhere, Turkey administered the Sinovac vaccine to health workers on Thursday after it was approved for emergency use.
Health experts fear that public confidence has been undermined by a series of conflicting findings on efficacy, saying a lack of data is hampering their understanding of the vaccine’s action.
Turkish researchers reported 91.25% efficacy, 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, just to later explain that it is only a partial picture. On Tuesday, it was announced that the effectiveness is 50.4% for all symptomatic infections, including very mild infections where people do not need clinical help.
Philippine President Rodrigo Duterte defended the Sinovac sting, claiming it was “as good as any other vaccine invented by the Americans or the Europeans”. He said on Thursday there had been a scramble for vaccines and “rich countries have bought all the supplies”.
There are several possible reasons why the findings vary so much, including the size of the trials, the composition of the participants, and the duration of observation after vaccination. The trial in Brazil was by far the largest, with 13,000 participants. However, it only recruited health workers, who may be more attentive to any symptoms and more exposed to the virus than others.
Lorenz von Seidlein, an associate professor in the tropical medicine research unit at Mahidol University in Thailand, said the decision to publish findings for certain subgroups also skewed findings. ‘The more you cut [findings] in smaller groups, the power of the study is diminished, and the chances of it being a false finding therefore increase, ‘he said.
The finding of 100% protection against serious diseases in the Brazil study was not statistically significant, he added – a point that would be picked up if the interim results for peer review were presented.
The Brazilian Sinovac trial is not the only case where subgroup analysis is presented. The vaccine, developed by Oxford University and AstraZeneca, also reported two different success rates. It showed 62% efficacy when two full doses were administered to adults of all ages, and 90% in a subgroup of participants not older than 55 who received half a dose, followed by a booster.
Sinovac has been criticized for providing less information than Western vaccine manufacturers. The company said that not all trials were designed the same way, but that it illustrated that the vaccine was safe and effective.
Dr Thiravat Hemachudha, head of the Thai Red Cross Health Center for Emerging Infectious Diseases, said it is possible that variants of the virus could also affect outcomes. “We can not look at the data and only see the numbers,” he said. “In Brazil, the variant may differ from the variant in the USA or England.”
The Thai government, which reintroduced restrictions after a new wave of business erupted last month, said it was seeking more information from Sinovac on the Brazil report, but did not change its plans.
Malaysia, where many areas have been re-locked due to an increase in cases, also looked at the Sinovac vaccine, but said it would review the company’s clinical data before proceeding.
Indonesia, which has recorded nearly 25,000 deaths, began vaccinating health workers this week. “We are not waiting for a better vaccine because we do not know when it will come in Indonesia,” Health Minister Covid’s vaccination spokesman Dr. Siti Nadia Tarmizi, said. She said that if you delay further, the number of deaths could increase.