Results of a direct comparison of one- and two-dose regimens will not be available until 2025.

At least 24 countries, including Mexico, Tonga and Guyana, have shifted to the one-dose approach, according to the World Health Organization.

The new evidence may convince more countries to adopt the strategy.

“What we had predicted was that this would be most interesting for the low- or middle-income countries,” said Paul Bloem, a senior adviser on HPV vaccination programs at the W.H.O. But high-income countries like Britain and Australia were among the first to change their policies, he noted.

The W.H.O. estimates that if widely deployed, a single-dose strategy could prevent 60 million cervical cancer cases and 45 million deaths worldwide over the next 100 years.

Cervical cancer is the fourth most common type of cancer in women worldwide, with an estimated 604,000 new cases in 2020, according to the W.H.O. The disease killed an estimated 342,000 women in 2020, more than the number who died during pregnancy or childbirth.

“This is a real killer of women,” said Dr. Seth Berkley, chief executive of Gavi, which funds immunization programs in lower-income nations.