The US has “the potential to go into a fifth wave” of coronavirus infections, said top infectious disease expert Anthony Fauci amid the rising cases due to the newly detected Covid variant Omicron and stagnating vaccination rates.

According to Fauci, the Omicron variant shows signs of heightened transmissibility, the Guardian reported.

Last week, the World Health Organisation (WHO) classified the latest variant B.1.1.529 of SARS-CoV-2 virus, now with the name Omicron, as a “Variant of Concern” (VOC). First detected from Botswana, in Africa, it has since spread to various countries in Europe, including Belgium, the Netherlands, France and the UK, in Australia and Canada among others.

Fauci pointed to how Covid case numbers rose dramatically in South Africa, where Omicron was discovered, over a short period.

According to media reports, genome sequencing and other genetic analysis have shown that the B.1.1.529 variant was responsible for all 77 of the virus samples analysed from Gauteng in South Africa, collected between 12 and 20 November. It is now also emerging in all other provinces.

“You were having a low level of infection, and then all of a sudden there was this big spike … and when the South Africans looked at it, they said, ‘Oh my goodness. This is a different virus than we’ve been dealing with,’ Fauci was quoted as saying on NBC news.

“So it clearly is giving indication that it has the capability of transmitting rapidly. That’s the thing that’s causing us now to be concerned, but also to put the pressure on ourselves now to do something about our presentation for this,” he added.

While the Centers for Disease Control and Prevention (CDC) has said no Omicron cases have been discovered in the US, Fauci noted that “as we all know, when you have a virus that has already gone to multiple countries, inevitably, it will be here.”

Any fifth wave of cases “will really be dependent upon what we do in the next few weeks to a couple of months”, Fauci was quoted as saying on CBS. The US has now about 62 million people in the country who are eligible but have not yet been vaccinated.

“Superimpose upon the fact that, unquestionably, the people who got vaccinated six, seven, eight, nine, 10 months ago, we’re starting to see an understandable diminution in the level of immunity. It’s called waning immunity, and it was seen more emphatically in other countries before we saw it here.”

Fauci said an increase in immunisation rates and booster shots might prevent another surge — but the US had to act fast.

“So if we now do what I’m talking about in an intense way, we may be able to blunt that,” he said. “If we don’t do it successfully, it is certainly conceivable and maybe likely that we will see another bit of a surge. How bad it gets is dependent upon us and how we mitigate it.”