The omicron surge seems to be slowing in much of the world, but a coronavirus subvariant that scientists believe is even more contagious is on the rise, and a decline in testing has muddled the global picture, the World Health Organization said.

New cases worldwide dropped 19% from Feb. 7-13, compared with the week before, according to the agency.

The WHO also said the omicron subvariant, BA.2, appeared to be “steadily increasing” in prevalence and that BA.2 had now become dominant in several Asian countries, including China, India, Pakistan, Bangladesh and the Philippines. Denmark was the first nation to report that BA.2 had overtaken BA.1, the omicron version that first swept through the world.

Scientists have said there is no evidence that BA.2 is more lethal than BA.1, although BA.2 could slow omicron’s decline. Vaccines appear to be just as effective against BA.2 as they are against other forms of omicron.

BA.2 now accounts for roughly 1 in 5 new omicron cases recorded across the world, according to the WHO.

The omicron wave has yet to crest in what the agency calls the Western Pacific region, which includes Oceania, the Pacific islands and East Asian countries such as China and South Korea that recently celebrated the Lunar New Year, a holiday period that typically involves large family gatherings. Cases in the region rose 19% last week, the WHO reported.

In the Pacific, two island nations that had no confirmed cases until recently are now grappling with the arrival of the virus. In Tonga, an outbreak began after ships brought aid to help the country recover from a volcanic eruption and tsunami in January. And the Cook Islands reported its first case last week.

The WHO said caseloads were falling in the other regions. But cases are still rising in parts of Europe, including in Slovakia, Latvia and Belarus. And in Russia, new cases have increased by 79% over the past two weeks, according to the Center for Systems Science and Engineering at Johns Hopkins University.

On Wednesday, Maria Van Kerkhove, the WHO’s COVID-19 technical lead, cautioned that a drop in testing rates around the world has meant the reported global case numbers might not reflect the true spread of the virus.

“We need to be careful about interpreting too much this downward trend,” she said. She said the bigger concern was the increase in reported deaths from COVID-19 for the sixth week in a row.

The WHO’s Eastern Mediterranean region, which includes the Middle East, reported the most fatalities, and the Western Pacific region reported the second most, according to the WHO.

In the Americas, many countries did not move fast enough to slow the transmission of BA.1, WHO officials said Wednesday, and they must be better prepared for whatever version of the coronavirus comes next.

“This will not be the last variant, and the future of the pandemic is still extremely uncertain,” said Dr. Carissa Etienne, director of the WHO’s Pan American Health Organization, adding that “a new variant could emerge at any time.”

This article originally appeared in The New York Times.