Earlier this year, the medical journal The Lancet confirmed the high efficacy of the Sputnik V vaccine. Several Latin American countries believed this would help them immunize their population faster.

Russia — the country behind the production of the Sputnik V — has a close relationship with certain countries in the region. The low production cost of this vaccine made it more affordable than those produced by Pfizer or Moderna.

However, today there is uncertainty regarding the massive application of the second dose of Sputnik V.

The next batch of Sputnik V just arrived in Venezuela. pic.twitter.com/EhWPG2C2T8

— Sputnik V (@sputnikvaccine) April 24, 2021

Six Latin American countries had begun distributing it by mid-2021: Argentina, Bolivia, Mexico, Nicaragua, Paraguay and Venezuela. But their health authorities have extended the interval between the first and the second doses.

The general rule is to wait 90 days between the two shots, but this might not be the case now, given the production uncertainty. Broadening the vaccine interval has triggered alarms as to a probable loss of immunity for those who received the first dose.

“Immunity is a result of the production of neutralizing antibodies and, until now, it is supposed to last for at least six months. Depending on the patients’ age and background, we believe it could be more,” said doctor María Alejandra Torres Vieira, a hematologist in Venezuela.

She explained the effectiveness of one dose is not very high and depends on the vaccine.

“That’s why a second dose [is necessary]. Its objective is to increase the [thermal] amplitude and the total number of antibodies in general, which is much higher. [After the second dose, the vaccine] reaches the 90 percent [immunity] that we want.”

The hematologist said the Venezuelan government “has broadened the interval because it no longer has vaccines. Some countries have delayed the second dose for three months to cover more people with the first shot. It has been a political decision rather than a scientific one.”

The decision allows more people to have partial protection and buys time for laboratories to produce second doses.

According to Torres Vieira, immunity is not lost by not applying the second dose.

Moscow confirmed in May that it developed a single-dose vaccine with 79.4 percent efficacy. Some people believe that the first dose of Sputnik V is the equivalent of the recently released Sputnik Light. But there is no scientific consensus regarding this topic.

With vaccination campaign going in full swing in #Argentina we’d like to wish a good health to all Argentinians!

Gracias por las fotos a @FrankPol18, @jckopri, @julireplasexta, @eugeniavivas pic.twitter.com/SItXxYKrd0

— Sputnik V (@sputnikvaccine) June 11, 2021

Flor Helene Pujol, the head of the Molecular Virology Laboratory at the Venezuelan Institute for Scientific Research (IVIC), said that “the [Sputnik V] first dose is equivalent to the Sputnik Light.” But Torres Vieira believes that the Sputnik V “has two different doses, with two different adenovirus vectors. Sputnik Light is more like the second dose of Sputnik V.”

The population that got the first dose of the Russian vaccine awaits a resolution.

“I feel concerned. I hoped to resume my life after a year and a half in quarantine, and now, I still cannot. I do not feel protected,” said María Pelayo, a Venezuelan senior. “Much less with the new, more contagious variants of the virus that are circulating.”

Pelayo should have already received her second dose, but she has not heard from the health authorities.

“The vaccines do not lose their effect. Yes, as time goes by, the antibodies weaken, but it [the Sputnik V] was never thought of as a single-dose vaccine. Both doses are going to be completed,” said Carla Vizzotti, Argentina’s Minister of Health, who has been criticized for the second-dose delay.

As more than 6 million people are waiting for their second dose in the Patagonian country, various voices within the scientific community suggest combining vaccines.

“The Gamaleya Center [in charge of developing Sputnik vaccines] has said that Sputnik Light is 70 percent effective,” said Pujol. She explained the Sputnik Light could be used as a second dose, given the success of a previous combination of AstraZeneca and Pfizer, “which was safe and created a more robust antibody response. However, the lab should conduct a clinical trial to confirm safety and immunogenicity.”

“Recent studies show that AstraZeneca shots have been combined with Pfizer with a very efficient result,” said Torres Vieira. “The best possibility, for now, is that those who had the first dose of Sputnik V could receive the Johnson & Johnson shot [as the second dose], which at the end of the day is a single-dose vaccine and would be perfect,” she said.

According to the World Health Organization’s estimates, a particular area achieves herd immunity when 60 percent to 70 percent of its population is vaccinated. In Latin America, as of mid-June 2021, only Chile and Uruguay are within that range.

Latin America has been one of the regions most affected by the pandemic, reaching 1 million deaths in May 2021.

(Translated and edited by Gabriela Olmos; edited by Fern Siegel)