September 4, 2020 at 7:45 PM EDT

Initial trial of Russian vaccine reports antibody responses, though scientists caution larger studies still needed

All participants in an early stage-trial of Russia’s experimental covid-19 vaccine successfully produced antibody responses, according to initial results published Friday by the Lancet, a leading medical publication.

Moscow warmly welcomed the results, following criticism last month over its licensing of the vaccine for domestic use despite that large-scale trials on it had not yet even begun. But the Lancet findings also raised some red flags for scientists who expressed concern about the sample size and lack of a testing control, among other limitations.

In the study, Russia’s “Sputnik-V” covid-19 vaccine was tested on 76 participants divided between two trials conducted between this June and July. All participants recorded antibody responses and no negative effects were detected.

Naor Bar-Zeev, an infectious-disease expert at the Johns Hopkins Bloomberg School of Public Health who was not involved with the research said the work “was conducted very well and carefully, but it’s a small study with a small number of people.”

He said these results were on par with findings from phase one and two trials conducted in small populations in Great Britain and China. Like the Russian trials, those studied what are known as viral-vectored vaccines, in which a harmless virus delivers a gene to help the immune system recognize the coronavirus. All are awaiting the results of larger, phase three trials.

Bar-Zeev, with his Johns Hopkins colleague Tom Ingelsby, wrote in a commentary also published Friday in The Lancet there were “notable” limitations to this work, including a disproportionate number of white men.

“Much more remains to be learned” from the randomized phase three trial approved by Russian health authorities in late August, they wrote, adding they hoped the larger trial, of 40,000 civilian volunteers, would be “broadly inclusive” of at-risk groups.

Bar-Zeev cautioned that this vaccine — like those being tested in the U.S. and elsewhere — runs the risk of being too understudied in the rush for approval. There’s a potential danger in speeding to license vaccines unless they prevent not only disease, but transmission, he said.

By Ben Guarino and Miriam Berger

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