More Omicron subvariants detected in US

Two new coronavirus variants sweeping South Africa, known as BA.4 and BA.5, are likely to evade vaccines and natural immunity from previous infections and have been identified in the United States, according to health officials.

In South Africa, the two new variants replaced the BA.2 strain in less than a month. They are now responsible for a new spike in South Africa's COVID-19 cases.

The subvariant, known as BA.2.12.1, which makes up nearly half of COVID-19 cases, is raging in the US, said the Centers for Disease Control and Prevention. The new Omicron subvariants BA.4 and BA.5 have spread to more than 20 countries across North America, Asia and Europe, including a handful of cases of each strain in the US.

Less than 1 percent of US cases from April 17-23 are related to BA.4 and BA.5, but the CDC said the two are labeled as variants of concern.

Experts in South Africa now expect a fifth COVID-19 wave within weeks even though an estimated 90 percent of the country's population has immunity to earlier Omicron variants either due to surviving a natural infection or through vaccination.

Meanwhile, COVID-19 positivity rates in parts of New York City are over 20 percent again. The transmission rate has risen to levels last seen in late January, up almost 20 percent in a week and almost 90 percent in a month. The city raised its alert level to "medium" last week.

US President Joe Biden was planning to convene world leaders for a COVID-19 summit on Thursday to ramp up their coronavirus relief efforts for poorer countries.

A group of former heads of state and Nobel laureates are calling on the US to immediately commit $5 billion to combat the pandemic.

"I want America to recognize that the disease is not over anywhere until it's over everywhere," said Gordon Brown, a former British prime minister who is leading the push for funding, in an interview on Monday, as reported by The New York Times.

The meeting comes as the Biden administration is struggling to secure additional funding from Congress to support its own coronavirus relief efforts at home and abroad.

Ahead of the summit, Biden called on upper-middle and high-income countries to donate $2 billion in coronavirus treatments, like the Paxlovid pill, and $1 billion in oxygen supplies to poorer countries, CNN reported.

US health authorities and researchers are investigating why some COVID-19 patients relapse after taking Paxlovid, Pfizer's antiviral pill. Since its authorization last December, the pill has become a go-to COVID-19 treatment. Some 80,000 people in the US have taken it, Pfizer said.

On Tuesday, Microsoft co-founder Bill Gates and NATO Secretary-General Jens Stoltenberg are among the latest figures to test positive for COVID-19.

Agencies contributed to this story.