Chinese drug maker Sinopharm has finally published the interim results from a phase 3 trial of its Covid-19 vaccine after more than 200 million doses have been administered worldwide.
The study, published in the Journal of the American Medical Association on Wednesday, has finally answered scientists' calls for greater transparency, but the results do not cover some of the most vulnerable groups, reports the South China Morning Post.
Trial data shows a vaccine made by Sinopharm's Beijing subsidiary, which has been approved by the World Health Organization for emergency use
, could offer 78.1% of protection against symptomatic Covid-19 but the rate dropped to 73.5% after taking asymptomatic cases into account. Another vaccine by the company's Wuhan subsidiary, which is in the process of applying for WHO emergency use licensing and has been conditionally approved for general use in China, had 72.8% efficacy against symptomatic cases and 64 cent including asymptomatic ones.
The results were based on data collected from 40,411 participants in the United Arab Emirates and Bahrain last year.
The trial participants, mostly healthy 18-59-year-olds, were equally divided into three groups inoculated with the vaccine from the Beijing subsidiary, the Wuhan subsidiary or a placebo.
A total of 142 symptomatic cases were recorded, 26 from the Wuhan vaccine group, 21 from the Beijing vaccine group, and 95 from the placebo group.
A small number of participants above 60 years old were recruited, around 200 in each group.
Only two severe cases were identified in the placebo group, and none in the two vaccinated groups, which the researchers said did not provide enough data to make a conclusion.
"These results should be interpreted with caution given the small number of incident severe cases," the authors wrote. "Conclusions about prevention of severe cases cannot be made."
Immunologist Ashley St John, an associate professor at Duke-NUS Medical School in Singapore, said the low number of severe cases could be down to the low number of elderly participants or those with comorbidities, but a higher number of severe cases may have generated more confidence.
"Certainly they don't have enough data on severe cases, and from a statistical standpoint we would need to see more cases to have a better idea how well this vaccine protects against severe disease," St. John said.
"When you have values like two or three out of hundreds [for severe cases], they don't give you confidence that it's not just a random event."
Vaccinologist Nikolai Petrovsky, a professor at Flinders University in Australia, said the fact that the only two serious cases were in the placebo group indicated a "positive direction", but agreed the numbers were not big enough to make a "statistical claim of difference".
But he added this tended to be the case for the trials of currently available vaccines.
"None of the trials that have been undertaken to date were statistically powered to look at serious illness or death. The numbers [of such cases] were too low," he said.
No death was reported in any group so no protection rate against death could be calculated, but Petrovsky said: "It doesn't mean it doesn't protect against death, but we just can't say anything about that from the trial data."