Coronavirus cases and deaths in Africa have fallen to their lowest levels since the start of the pandemic, marking the longest decline for the disease, according to the World Health Organization.

The United Nations health agency said in a statement on Thursday that COVID-19 infections due to a surge in omicron had “fallen” from a weekly peak of more than 308,000 cases to less than 20,000 last week. Cases and deaths fell 29% and 37%, respectively, last week; the number of deaths fell to 239 from the previous week.

“Since April 2020, this low level of infection has not been seen in the early stages of the pandemic in Africa,” the WHO said, noting that no country in the region is currently experiencing an increase in COVID-19 cases.

However, the agency warned that there is “a high risk of a new wave of new infections” as winter approaches in the southern hemisphere country. The coronavirus spreads more easily in cooler temperatures when people are more likely to gather in large numbers indoors.

“With the virus still circulating and the risk of new and potentially deadlier variants emerging, pandemic control measures are essential to effectively respond to a surge in infections,” said WHO Africa Director Dr Matshidiso Moeti.

The drop in Africa is in line with a global drop in COVID-19 numbers, although in China officials fear at least 15 million people have been banned from going out despite a “zero-tolerance” approach sparked by a three-week lockdown in Shanghai.

Not a Modern Healthcare subscriber? Register today.

The measures have led to frustration among Shanghai residents over shortages of food and medicine. This week, authorities also closed access to Guangzhou, an industrial hub of 19 million people close to Hong Kong, where other cities are cutting ties to the outside world or closing factories and schools.

Meanwhile, US scientists have warned that the country could be on the verge of a wave of cases caused by the omicron sub-variant BA.2, which has peaked in Europe. The country is expected to soon mark at least 1 million American deaths from COVID.

Earlier this week, the WHO said scientists in Botswana and South Africa had detected new forms of omicron variants, labelled BA.4 and BA.5, but it was uncertain whether they were more contagious or dangerous.

To date, new versions of omicron have been detected in 4 individuals in Botswana and 23 individuals in South Africa. Outside Africa, scientists have confirmed cases in Belgium, Denmark, Germany and the UK. The WHO said that so far, there is no evidence that the new sub-variant spreads any differently than the original omicron variant.

Despite repeated warnings by WHO Director-General Tedros Adhanom Ghebreyesus that the coronavirus will devastate Africa, the continent has been one of the continents least affected by the outbreak.

In an analysis released last week, the WHO estimated that as many as 65% of people in Africa are infected with the coronavirus, saying that unlike many other regions, most infected people on the continent are showing no symptoms.

Scientists at the WHO and elsewhere speculate that factors such as Africa’s younger population, lower rates of chronic diseases such as heart disease and diabetes, and warmer weather may help it stave off a bigger wave of disease. Still, some countries have seen significant increases in unexplained deaths, suggesting authorities are missing many COVID-19 cases.