The makers of a leading Russian vaccine candidate, Sputnik V, said on Tuesday that it showed an efficacy rate of 95 percent in preliminary results from a clinical trial, which would put it at the same level as or better than three other vaccines that have yielded results in recent weeks.
However, that figure was based on an unspecified small group of volunteers within the ongoing Phase 3 trial of the vaccine, and the vaccine makers did not specify how many people with the vaccine or the placebo got sick. When the trial is done, the company said, they will release more complete data.
While it was hard to immediately assess the efficacy of the vaccine based on the announcement and the fact that the Phase 3 trials are not complete, the news promised to add to the flurry of excitement over the promise that vaccines could bring the coronavirus pandemic to an end.
The American and German team of Pfizer and BioNTech and the American company Moderna have announced efficacy rates of 95 and 94.5 percent, respectively. And AstraZeneca and the University of Oxford said on Monday their vaccine is either 62 percent or 90 percent effective, depending on the manner in which the doses were given.
Russia registered the vaccine for emergency use in August before beginning a clinical trial to measure its efficacy, shortcutting the usual process and drawing international criticism. President Vladimir V. Putin claimed it was the first vaccine in the world to receive government approval.
Russia has marketed its vaccine mostly in former Soviet states and countries with developing economies, saying the cost of one dose will be less than $10 for international markers. Officials said that vaccine makers have received orders for 1.2 billion doses from around 50 countries. The Russian Direct Investment Fund has said that about 10,000 people have been inoculated under the emergency-use approval.
On Nov. 11, the government-backed Russian Direct Investment Fund announced that an analysis of the first 20 volunteers indicated an efficacy rate of 92 percent. On Tuesday, the fund provided a similar estimate with more details. They analyzed 18,794 volunteers who have received both injections of the two-dose regimen; 14,095 got the vaccine and 4,699 got the placebo.
A week after the second dose, they found 39 cases of Covid-19, with only eight of the volunteers who got sick having received the vaccine. Based on the ratio of volunteers who got the vaccine to the placebo, the researchers estimated the efficacy at 91.4 percent.
But in their announcement, the fund said that researchers also looked at an unspecified number of volunteers three weeks after the second dose. In those volunteers, they calculated an efficacy rate of 95 percent.
The researchers will take another look at the results when they reach 78 cases of Covid-19 in the volunteers.
Some experts expressed skepticism about the announcement, which was based on an incomplete dataset and apparently not compiled during a regularly scheduled review of the trial results.
“That’s not how it should be done,” said Dr. John Moore, a virologist at Weill Cornell Medicine. “It seems to me what they’re doing is slicing and dicing and data-dredging to come up with the 95 percent figure.”
In August, the Russian Direct Investment Fund named the vaccine Sputnik V for the first satellite launched by the Soviet Union, though at the time, other vaccines were further along in development.
Russian scientists have begun Phase 3 clinical trials on two other vaccines.