By Michael Daly
A new Omicron variant - XBB.1.5 - is surging in the United States, with the Centers for Disease Control projecting it accounted for about 40 percent of US Covid cases in the last week of December.
In the US northeast about 75 percent of confirmed cases were thought to be XBB.1.5.
NBC News, however, quoted a CDC official saying there was no indication it caused more severe illness than other Omicron variants.
While the number of people in hospital in the US with Covid was rising, areas with high levels of the new variant, such as the northeast, did not have a disproportionate increase in hospitalisations, Dr Barbara Mahon, director of CDC's Coronavirus and Other Respiratory Viruses Division, said.
The number of people hospitalised at this time is also well below last year's Omicron surge.
Most recent wastewater surveillance data for this country on the ESR dashboard is for 18 December. It doesn't show any XBB.1.5. The XBB variant, from which XBB.1.5 evolved, accounted for just 3.7 percent of the Sars-Cov-2 detected.
ESR genomics testing found XBB accounted for just 2.5 percent of cases tested in early December.
While the number of people being admitted to hospital is rising in the US, which is in the depths of winter, in New Zealand, where it's midsummer, reported case numbers have fallen as have hospitalisations.
The Guardian reported that XBB.1.5 seemed to have arisen in or around New York state in late October. It has also been detected in the UK, with surveillance indicating it made up at least 4 percent of Covid viruses being sequenced.
Ravi Gupta, professor of clinical microbiology at the University of Cambridge, told The Guardian he thought the new variant might drive an increase in cases, but he was not convinced that would necessarily cause an explosive wave of infections in the UK.
"I don't think there's any cause to panic. The main thing we worry about is the severity of the disease, and there is no evidence that it's more severe. People should, however, make sure they are up-to-date with their vaccines," Gupta said.
The publication also reported that XBB.1.5 is spreading more than twice as fast as the BQ.1.1 variant, which is one of the most common variants found in the UK.
XBB.1.5 had a mutation that changed part of the Covid virus targeted by many antibodies. The change made the antibodies less effective at neutralising the virus, it has been widely reported.
On Wednesday, Covid-19 Response Minister Dr Ayesha Verrall said she had not been advised the XBB.1.5 variant had been found in this country.
"In the US we know that that variant has become more prevalent in recent weeks. However, it's not clear if the areas where it's swung up are the same areas where there have been increased hospitalisations," Verrall said.
"So it's not clear to us that that poses a particular risk in our context."
She was asked about the variant after announcing New Zealand would not be requiring arrivals from China to test for Covid.
In her announcement, Verrall said new Covid variants could arise across the world, not just China.
She said the growth of XBB.1.5 in the US was an example of why the government was reminding arrivals from all countries to test for Covid if they had symptoms.
Professor Peter McIntyre from the University of Otago said XBB.1.5 appeared to be similar to other variants of Omicron.
There was no evidence it caused more severe illness, although it may be more likely to cause infection, including in people who had been vaccinated or infected before.
The evidence demonstrated that vaccination with at least three doses, specially if that was accompanied by infection, provided long-term protection against severe illness, McIntyre, who is the author of more than 450 publications relating to vaccine and vaccine preventable disease topics, said.
The combination of protection from vaccines and from infection is known as hybrid immunity. Research has found it can provide effective protection, but many questions, such as how durable it is remained to be answered.
New variants were not news any more, McIntyre said. What mattered was if there was any evidence that it caused not just breakthrough infection, but breakthrough infection that resulted in severe illness.
The main message for the great bulk of people, was that if you are an adult make sure you have had your third dose, and for older adults, to make sure they had their fourth dose, McIntyre said.
For the small number of people at risk of severe illness, other treatments were available. "The most important thing is to ensure those people get quick access to appropriate care."
Dr Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organisation at the University of Saskatchewan in Canada, tweeted that XBB.1.5 was another evolutionary advance by Sars-CoV-2.
That was what viruses did.
She did not expect to see big changes in terms of disease severity, since infections would happen in a population where people had been vaccinated and infected with Omicron.
"But that said, a wave of XBB.1.5 is just as bad as any Covid surge, especially with so many other respiratory viruses around (in the US)," Rasmussen said.
This story was originally published by Stuff.