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World Health Organization officials are holding a press conference on Friday to update the public on the coronavirus outbreak which has infected more than 88.2 million people across the world as governments race to roll out vaccines.

The briefing comes as the United States reported its deadliest day yet of the pandemic, with more than 4,000 people dying in one day. Around the world, governments that secured doses of the vaccines produced by Moderna and Pfizer–BioNTech are racing to administer shots as quickly as they can.

Officials at the WHO and immunologists around the world are closely watching the genomic sequence of the virus as new variants spread in some parts of the world. A strain that was first discovered in the United Kingdom has spread to the U.S. and other countries, though it has yet to conclusively gain ground outside of the U.K.

Another strain first discovered in South Africa is worrying experts because vaccines and certain Covid-19 treatments may not be as effective against that strain as other ones.

Read CNBC’s live updates to see the latest news on the Covid-19 outbreak.