Turkish authorities announced on Thursday that a vaccine by the Chinese company Sinovac has an efficacy rate of 91.25 percent, but the discovery was based on preliminary results from a small clinical trial and none of the data was published in a newspaper or posted online.
The announcement came a day after another ambiguous press conference, also about the Sinovac vaccine in Brazil. The authorities were expected to provide detailed results from another trial, but reported only that the vaccine had an efficacy rate in excess of 50 percent.
A total of 7,371 volunteers were involved in the Turkish study, but the efficacy data provided by Serhat Unal, an infectious disease specialist, was based on just 1,322 participants, 752 of whom received a real vaccine and 570 of whom received the placebo.
Dr. Unal said 26 of the volunteers who received the placebo developed Covid-19, while only three of the vaccinated volunteers fell ill. He and his colleagues did not share their data in writing.
“Now we are sure that the vaccine is effective and safe for the Turkish people,” said Fahrettin Koca, the health minister.
Sinovac did not issue a public statement about the trial, nor did he comment on the trial in Brazil.
The small number of volunteers on which Turkish researchers based their calculation of effectiveness raised questions about the certainty of their conclusions. The more people participate in a clinical vaccine trial, the stronger their statistical power becomes.
Pfizer and BioNTech, on the other hand, presented data on 36,523 people to show that their vaccine has a 95 percent effectiveness rate. For the vaccine, 162 people who received the placebo developed Covid, compared with eight in the group that received the vaccine.
Turkey has signed an agreement with Sinovac for 50 million doses of the vaccine. The first three million doses are scheduled to arrive in Turkey on Monday, Koca said. Koca said Turkey will also receive 4.5 million doses of the Pfizer-BioNTech vaccine by the end of March. About 1 million doses are expected to arrive by the end of January, he said.
CoronaVac, as Sinovac calls its vaccine, is made up of dead coronaviruses. The method is one of the oldest for making vaccines, used by Jonas Salk in the 1950s to make a polio vaccine. Once viruses are inactivated by chemicals, they cannot make people sick, but they can cause the immune system to produce antibodies that can provide long-term protection against live viruses.
Sinovac developed CoronaVac in early 2020 and then carried out a series of clinical tests. They published their results in November. There they reported that the vaccine appeared safe and elicited an immune response against the coronavirus.
The company then passed Phase 3 testing in Brazil, Indonesia and Turkey, three countries with high Covid-19 rates.
Health officials in Brazil said on Wednesday that the Chinese vaccine passed safety and efficacy tests that would pave the way for its use in Brazil, but delayed the release of detailed clinical trial data in Brazil underlying these findings, citing a contractual agreement with Sinovac. Dimas Covas, director of the Butantan Institute, who conducted the tests, said a joint announcement could happen in two weeks.
“Today is a historic day for science and for Brazilian health,” Jean Gorinchteyn, São Paulo State Health Secretary, told reporters at a news conference. “This will allow us to save the lives of millions of people, not only in Brazil, but around the world.”