MEXICO CITY — Russia has been having so many problems producing second doses of its Sputnik V coronavirus vaccine that it probably will be unable to supply enough to people who already got the first dose, Mexican officials said.

It’s the latest account of production problems for Sputnik V, which the Russian government has been promising to other countries but has not been able to supply in sufficient quantities.

Sputnik is unusual among coronavirus vaccines in that the two doses are different and not interchangeable.

Mexico’s assistant health secretary, Hugo López-Gatell, said the Russians have found that the first adenovirus grows much more quickly than the second.

López-Gatell said Russian scientists are now suggesting abandoning the idea of giving the two separate Sputnik V shots several weeks apart and instead giving a second booster shot six months later.

“Over the course of months, the quantity of first doses they managed to produce got out of alignment with the quantity of second doses they were able to produce,” López-Gatell said.

The Russian Direct Investment Fund, Russia’s sovereign wealth fund which has bankrolled Sputnik V, denied the Mexican reports.

“The manufacturing of both components of Sputnik V is being upscaled in Russia and abroad to fully meet the rising demand for the vaccine internationally,” the fund said in a statement.