The government announced on Monday that all adults in the United Kingdom will be able to get their booster Covid-19 vaccine doses three months after their second shot, a dramatic increase in the country’s immunization drive that comes amid concerns about the Omicron variant.

Boosters were previously only available for a minimum of six months after a second dose, for people over the age of 40, and for people over the age of 16 who had underlying health conditions.

By reducing the gap to a minimum of three months, the UK will soon have one of the shortest intervals in the world.

On Monday, Health Secretary Sajid Javid confirmed in Parliament that he had accepted the move, hours after the UK’s vaccination advisory body recommended it. England is also reintroducing a mask mandate in stores and on public transportation beginning on Tuesday, a move announced over the weekend that was also prompted by Omicron concerns.

The new step will raise concerns about geographic disparities in the effort to protect people from Covid-19, which has been highlighted since the concerning new variant was discovered in southern Africa, where vaccination rates are lower.

“We’ve always known that a concerning new variant could pose a threat to the progress we’ve made as a nation,” Javid told lawmakers.

“We’re learning more about this new variant all the time,” he said, adding that there’s “a reasonable chance that our current vaccines may be impacted.”

According to official data, the United Kingdom has administered 17 million booster shots, inoculating 31 percent of its over-12 population.

The expansion of the rollout means that tens of millions of people are now eligible, much sooner than they would have been previously, and the country is once again in a position distinct from the rest of the world when it comes to vaccines.

Most other countries that have deployed boosters have invited people to return six months after their second dose for a third shot. The United Kingdom previously broke the mold with its initial rollout in January, offering first and second doses 12 weeks apart in an effort to provide more people with some level of protection sooner.

The possibility of a new variant emerging in a region of the world with lower vaccination coverage has been warned about for months, prompting some to advocate for richer countries to prioritize donating surplus doses over kicking off booster rollouts.

Only 7.5 percent of people in low-income countries have received at least one dose of the coronavirus vaccine, according to the World Health Organization (WHO). The proportion of populations that have received at least one vaccine dose ranges from 5.6 percent in Malawi to 37 percent in Botswana, among the eight countries most affected by travel bans related to the Omicron variant.

Rosena Allin-Khan, Labour’s shadow health minister, told Javid in Parliament that “this variant is a wake-up call” and that “no one is safe until all of us are safe.” She chastised Prime Minister Boris Johnson’s government for failing to implement mitigation measures and for failing to press for the distribution of doses to poorer countries.

Javid, on the other hand, said Allin-Khan had “misjudged the tone” of the debate, adding, “Surely she isn’t blaming the UK government for the emergence of this new variant.”

According to Michael Head, a senior research fellow in global health at the University of Southampton, the emergence of new variants is a “natural consequence of being too slow to vaccinate the world.”

“Like in Sub-Saharan Africa, we still have large unvaccinated populations that are vulnerable to large outbreaks,” he said.