With some countries across Africa continuing to see increases in Covid-19 cases, there's concern about a new variant of coronavirus in South Africa.

The World Health Organization (WHO) has called on African nations to boost their surveillance of the virus to detect any mutations that may occur.

Daily new case numbers have passed the peak of mid-July, although there are now signs that cases are starting to go down again.

There's been an average increase of 17% in weekly new cases and 30% in new deaths in South Africa over the four weeks up to 17 January, according to the Africa Centers for Disease Control (CDC).

There's concern that infections are being driven in part by a new strain known as 501.V2.

Scientists are still studying this new variant, how it transmits and how it might behave in response to vaccines.

"Initial analysis indicates that the variant... may spread more readily between people," according to the WHO.

However, it doesn't appear to cause more serious illness.

The South Africa variant has so far been reported in four other African countries - Botswana, Zambia, the Gambia and Kenya.

At the end of December, South Africa became the first country in Africa to record more than a million Covid cases.

The authorities have announced new restrictions, and closed land borders to most travellers until mid-February.

The WHO says cases in its Africa region (which excludes Morocco, Tunisia, Libya, Egypt, Sudan, Djibouti and Somalia) have been increasing since the middle of September.

It adds that "steeper increases have been observed since late November. "

The Africa CDC says that over the four weeks up to 17 January, apart from South Africa, there'd been significant increases in new cases in both Egypt and Nigeria - up by an average of 20% and 23% respectively.

In Nigeria, scientists have also identified a new variant of the virus, although they say there is currently no evidence to indicate it is contributing to increased transmission.

However, cases in Nigeria have been on an upward trend since early December.

The head of the Nigeria CDC, Chikwe Ihekweazu, says the country is reaching "a critical level" at which its hospital capacity will no longer be able to cope with the more serious cases.

There are also significant variations across the continent, with countries at different stages of a resurgence of the virus.

For example, cases rose again in Kenya, Ethiopia and Uganda at different points in the latter part of 2020, but recorded daily infection rates have subsequently fallen.

Cases have however been steadily increasing in Zambia, Rwanda and Malawi.

The WHO says testing in Africa is still low compared to other regions, and there's also concern that irregular levels of testing over time may be masking the true spread of the virus.

There are wide variations in testing rates and while some countries have reduced testing, others have maintained or even increased it.

Of the bigger countries, South Africa has been doing the most and Nigeria doing relatively few tests per capita, according to Our World in Data, a UK-based project which collates Covid-19 information.

However, in some countries there are insufficient or no data available on testing to know how much is being done.

According to the Africa CDC on 17 January, there'd been an decrease of 22% in the total number of tests done over the previous week.

Ten countries accounted for 70% of the tests conducted - South Africa, Morocco, Ethiopia, Kenya, Nigeria, Egypt, Uganda, Cameroon, Rwanda and Zambia.

The King's Global Health Institute, which tracks the pandemic in sub-Saharan Africa, says that testing activity in some countries fell back after the first wave of the virus had subsided.

"Those countries that cut back on testing after the first wave will...have had less extensive and timely intelligence from surveillance," it says.

The reported death rate per capita on the continent has been low compared with other parts of the world, despite the weak health infrastructure in many African countries.

There could be a number of reasons for the relatively low figures:

But there are also issues - as elsewhere in the world - over how countries record deaths, making comparisons between them difficult, and questions about whether deaths are under-recorded.

Research from the South African Medical Research Council (SAMRC) looking at excess deaths there indicates that the number of people who had died from the virus in the country could have been under-estimated.

There were 83,918 excess deaths between 6 May last year and 5 January this year - that's the number of deaths in that period above what would have been expected.

While not all of these might be directly due to Covid, the number of recorded deaths from Covid-19 since the start of the pandemic was at just above 30,000.

And South Africa was just one of eight countries on the continent that the BBC found in a recent investigation had adequate death registration systems.

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