The World Health Organization (WHO) is warning that a new Covid-19 subvariant, XBB.1.5, is the most transmissible yet.

Roughly 75 per cent of new cases in the northeastern United States at the moment are cases of this subvariant.

At present, not much else is known about XBB.1.5, but early research suggests it is more “immune evasive” and contagious. Maria Van Kerkhove, the WHO’s COVID-19 technical lead, said on Wednesday that her organisation was concerned about the subvariant’s “growth advantage” in the northeastern United States as well as in Europe.

The WHO had another warning, too: Although the organisation said no variants of concern have emerged from the Chinese data, it admitted that it does not have “complete data” from China.

“We believe that the current numbers being published from China under-represent the true impact of the disease in terms of hospital admissions, in terms of ICU admissions, and particularly in terms of deaths,” the WHO’s emergencies director, Michael Ryan, said, according to the Guardian. China, which recorded just 22 Covid-19 deaths since December, insists that it is sending data in a quick and transparent manner.

Countries around the world are trying to figure out what China’s reopening means for their travel policies.

On Thursday, Germany joined the ranks of countries, among them the United States, France and Japan, with some entry requirements for travellers from China. German Health Minister Karl Lauterbach announced that the country will require “at least a rapid test” be taken for Chinese travellers to come from China to Germany.

The Chinese government had an announcement of its own on Thursday: After three years of being largely closed, on January 8, its border with Hong Kong will reopen, and up to 60,000 Hong Kong residents will be able to cross over into the mainland.

Hong Kong residents have in turn rushed to get vaccinated, worrying that the reopening of the border will bring with it a surge of new cases of Covid-19.

• A Tell report