Global authorities have reacted with alarm to a coronavirus variant detected in South Africa, called B.1.1.529, with the EU, Britain and India among those announcing stricter border controls as scientists seek to determine if the mutation is vaccine-resistant.
Since the COVID-19 outbreak, SARS-CoV-2, the virus that causes COVID-19, has changed over time. Most changes have little or no impact on their properties.
However, some changes may affect how easily they spread, their severity or the performance of vaccines against them.
This one has drawn scrutiny because it has more than 30 mutations of the spike protein that viruses use to get into human cells, UK health officials say.
That is about double the number of Delta, and makes this variant substantially different from the original coronavirus that current COVID vaccines were designed to counteract.
South African scientists say some of the mutations are associated with resistance to neutralizing antibodies and enhanced transmissibility, but others are not well understood, so its full significance is not yet clear.
UK Health Security Agency Chief Medical Advisor Dr Susan Hopkins told BBC radio some mutations had not been seen before, so it was not known how they would interact with the other ones, making it the most complex variant seen so far.
So more tests will be needed to confirm if it's more transmissible, infectious or can evade vaccines.
The work will take a few weeks, the World Health Organization's technical lead on COVID-19, Maria van Kerkhove, said on Thursday. In the meantime, vaccines remain a critical tool to contain the virus.
No unusual symptoms have been reported following infection with the B.1.1.529 variant and, as with other variants some individuals are asymptomatic, South Africa's NICD said.