Sputnik V is a controversial two-dose COVID-19 vaccine from Russia's Gamaleya Research Institute of Epidemiology and Microbiology. The vaccine is approved for use in roughly 60 countries and began international distribution in December 2020 and over 1 billion doses have been ordered as of May 6, 2021.

Despite reports from a February 2021 study that showed the vaccine's efficacy rate at 91.5%, a recent study found the vaccine was found to have an efficacy rate of 79.4% after only one dose of the two-dose vaccine. Russia's Ministry of Health noted that one shot can provide some protection in the short-term.

Russia calls the one-shot version of the vaccine 'Sputnik Light.' It has been approved for use in the country, which means Russia can administer one dose to a greater number of people and can cancel second doses while more of the vaccine gets manufactured.

The Sputnik Light study was observational, and less precise than a typical vaccine clinical trial. Importantly, the people getting the single dose weren't compared to a "control group" — people given a placebo for the shot, which is widely accepted as best practice when it comes to scientific studies of this nature. Researchers are now studying the one-shot dose using a control group.

Sputnik V uses a weakened form of an adenovirus, which is the kind of virus that causes the common cold in chimpanzees. (It's weakened so that it can't actually make you sick.) The adenovirus serves as a vehicle for getting the vaccine's key ingredient—a genetic code that triggers a COVID-19 immune response—into human cells. 

AstraZeneca and Johnson & Johnson use the same type of viral vector technology in their vaccines, but Sputnik V is slightly different.

Gamaleya Institute used one type of adenovirus in the first shot and another type in the second shot. The second type of adenovirus makes sure that, after becoming familiar with the vaccine with a first dose, the body still sees it as a foreign invader.

Sputnik V can be refrigerated and is reported to be lower cost than mRNA vaccines. The Gamaleya Institute reports no serious adverse side effects. The group has also noted the strong immune response created by the vaccine.

There is widespread concern about the safety and efficacy of Sputnik V. The vaccine was approved for use in Russia before the nation's drug safety review completed its analysis. President Putin of Russia announced the approval before phase I and II clinical trial data was published or peer-reviewed. At the time phase III trials had not even began.

Nearly every other vaccine must submit data from all three clinical trial phases before getting approved, so many scientists were skeptical about the rigor of research and data involved in Sputnik's trials.

Researchers have also noted some odd findings from the vaccine's trial studies. Participants who were given very different forms of the vaccine all had the same antibody and T-cell levels, despite being measured on different days. Scientists from several countries including Russia wrote an open letter citing their concern that the trial data had potentially been altered.

The Gamaleya Institute's team responded to these concerns in a letter published in the public health journal The Lancet, noting small sample sizes (38 people total) and the rounding of numbers within their data that caused irregularities in their results.

The Sputnik V team then published early results from phase III trials, which included over 18,000 participants who received two doses of the vaccine three weeks apart. The reported efficacy rate was 91.6% with no serious side effects. Scientists were again skeptical about this data, stating that an independent, outside review of findings could not have occurred if primary data for the study had never been published.

There have been questions about the protocols and participants involved in the trials as well. Some of these concerns caused Brazil to not approve Sputnik V, due to what the Brazilian government claims to be a lack of information, "serious" defects, "inherent risks," and little assurance about the vaccine's safety, efficacy, or quality.

In April of 2021, the nonprofit newspaper the EU Observer claimed four people had died and six people had severe side effects after being injected with Sputnik V, which a Russian leader denied could have been linked to the vaccine.

The European Medicines Agency (EMA) began reviewing data for the vaccine in March 2021 and needs access to a complete dataset before considering approving the vaccine for use in its countries. The Gamaleya Institute has been hesitant to provide this data to the EMA, according to Deutsche Welle. This is the case despite growing interest about the vaccine in parts of Europe, including potential orders from three countries which will not be filled unless EMA approval for Sputnik V is given.

Overall, researchers are optimistic about findings from Sputnik V and Sputnik Light trials, but are hesitant to place their trust, or their citizens' health, on the vaccine until the EMA approves it and more independent research and reviews are conducted.

As of April 21, 2021, the World Health Organization noted it "[I]s still receiving information from the Gamaleya National Center, the producer of Sputnik V candidate vaccine against COVID-19. WHO expert group, Technical Advisory Group (TAG) will assess this vaccine candidate for emergency use listing after the inspections have been finalized." This review also includes a joint effort with the EMA for on-site inspections from May 10 through to the first week of June 2021.   Inspections for good clinical practices are being undertaken in April, by a joint EMA (European Medicines Agency)/WHO team. On-site inspections will take place from 10 May until first week of June. This will assert "[T]hat the regulatory review process in the country of manufacture has held up to the highest standards." But accurate, reliable data is important here as reviews will be "[B]ased on availability of complete information and provide assurance of quality, safety and efficacy."

There has been substantial controversy surrounding the Sputnik V vaccine from Russia. Several of the concerns with the vaccine are rooted in its scientific findings and processes. Noted issues include the vaccine's fast development process, potential political influences, and public relations and protocol missteps. Due to the nation's early stage approval and public confidence in the vaccine, even before it had been properly tested, many are doubtful of findings despite positive studies in peer-reviewed journals.

Until more outside research is conducted by independent groups and published in scientific journals, groups like the WHO and other regulatory agencies likely cannot validate it safety and efficacy in an unbiased manner.