By Cassidy Morrison

The United States' top infectious disease expert Dr Anthony Fauci has warned that a new, more dangerous Covid variant could hit this winter.

Despite the steady decline of Covid viruses and deaths since the summer, Dr Fauci said Americans 'should not be surprised' if a highly transmissible variant emerges as the months get colder.

Fauci, who is set to retire from his post as director of the National Institutes of Health in the coming months, has become famous for his grim warnings about Covid surges, although this is the first such forecast he has issued in months.

People spend more time indoors with less ventilation during the winter months, making it easier for Covid to spread. The more the virus spreads and replicates, the greater chance it has at mutating to a new, more transmissible strain.

'We should anticipate that we very well may get another variant that would emerge that would elude the immune response that we've gotten from infection and/or from vaccination,' Dr Fauci added.

Dr Fauci has been painted by critics as a pessimist with little hope for the US' recovery from the pandemic.

He did not identify a specific variant, but Dr Fauci said past winter surges should be an indication that the US is at risk of enduring another one.

The cases of Covid have consistently ticked up in the colder months when people spend more time indoors with less ventilation and less personal space than when outdoors in the summer months.

'We are entering into the winter months, where no matter what the respiratory disease is, there’s always a risk of an uptick,' Dr Fauci said.

The likelihood of a winter surge is based on trends over the past two and a half years. The summer of 2021 saw a relative lull in case rates, creating a sense of security nationwide.

The summer lull was the calm before the storm that was the devastating omicron outbreak last winter.

The omicron variant was the most transmissible one recorded at the time due to an unusually high number of mutations on its genome.

At its peak predominance in January, omicron had accounted for nearly 1.3 million infections.

Cases and deaths have maintained downward trends since the summer. about 43,700 cases were reported daily during the week ending October 5, federal tracking shows.

The seven-day average number of deaths have hit 330, down from about 1,670 daily this time last year.

Several omicron subvariants have arisen since the surge began in December 2021. BA.5 currently accounts for more than 79 per cent of cases.

Another omicron cousin, BA.4.6 is becoming more prevalent, now making up for 13.6 per cent of cases.

The fear among infectious disease experts is that a new variant will prove capable of evading the protection conferred by vaccines, recovery from previous infection, or a combination of the two.

The BA.5 subvariant was determined to be about four times as effective at evading vaccine protection and is more likely to cause breakthrough infections than the BA.2 omicron subvariant.

But the omicron surge last winter did not result in an overwhelming wave of fatalities like that of previous surges due to a general population immunity that has been gained from vaccines and exposure to the virus.

Still, Dr Fauci said the current seven-day average number of deaths is unacceptable and must be brought down.

A new variant could become more adept at skirting the acquired immunity.

Federal officials are urging Americans 12 and older to get the new bivalent Covid booster shot that specifically targets the BA.5 subvariant.

It's also believed to be effective against the BA.4.6 subvariant.

But booster rates are lagging as pandemic fatigue grips America. Statements like President Biden's last month that 'the pandemic is over' has also undercut the vaccination campaign's message.

Preliminary data shows that roughly 11 million Americans, only 5.3 per cent of the 215.5 million people aged 12 or older who are eligible for the bivalent booster, have received one.