A ‘double mutant’ flu virus has been detected in the United States that could make medicines less effective, officials warn.
At least two Americans were infected with a new strain of H1N1, containing two major new mutations, last flu season, according to a study, in a warning sign that it may be gaining ground.
Worldwide, 101 cases of 15,000 infections tested (0.67 percent) were detected on five continents, in another sign that it is spreading.
CDC scientists call the strain a “dual mutant” because it carries two major mutations that make it up to 16 times more resistant to the leading flu antiviral, oseltamivir, which is prescribed to nearly all patients with the infection.
Flu viruses are mutating to become more resistant to oseltamivir, study suggests (stock)
There is no indication at this time that the strain is more infectious or more deadly than other viruses currently circulating.
H1N1 is the flu strain behind the 2009 flu pandemic, which killed 12,000 people and was transmitted from pigs to humans. It differs from the H5N1 strain that is currently causing alarm in official circles and is causing an outbreak among American cattle.
Although the strain was found to be more resistant to oseltamivir, further research showed that it had no effect on other antivirals for the treatment of flu such as baloxavir.
Scientists first detected an H1N1 strain that was more resistant to the flu, but had different mutations, in the US during 2007 and 2008.
No further cases were detected after the 2009 flu pandemic, but the new ‘double mutant’ strain shows possible re-emerging resistance to oseltamivir.
It comes amid concern among CDC officials about H5N1, who warn that if it spreads to humans, it could cause a major outbreak.
The H1N1 strain carries two mutations (I223V and S247N) that alter key proteins used by the virus to make copies of itself and that are the target of oseltamivir.
This means that the medicine becomes less effective, but is less able to stop the virus from making copies of itself.
It was unclear where the two American patients were located or whether they survived their infections, although both were likely tested for the virus while in the hospital.
For the study, published as an advance version in the CDC’s own journal Emerging infectious diseasesAgency scientists analyzed data on the genetic sequences of flu viruses.
During the 2023 to 2024 flu season, there were at least two Americans infected with the mutant strain the study found. The graph above shows how cases increased during the season.
These were sent to the agency or to GISAID, a global database on influenza infections.
Only a handful of the millions of flu infections are tested for strains each year, meaning many more people may be infected than the data suggests.
The first case of ‘double mutant’ infection was detected in Canada in May 2023, and the last was detected in Europe in February 2024.
The Netherlands recorded the most cases, 40 infections, followed by France, 24, Bangladesh, 11, and Oman and the United Kingdom, nine each.
In addition to the United States, Australia and Spain also recorded two infections with the virus.
The two American cases were detected by laboratories at the Connecticut Department of Health and the University of Michigan last fall and winter.
Several flu infections also had only one of the two mutations, which also conferred resistance to oseltamivir.
The researchers warned that these viruses could acquire the other mutation through a process known as recombination.
This occurs when two different flu viruses infect a cell at the same time and then exchange genetic material with each other.
The researchers wrote in their report: ‘Our study highlights the need to closely follow the evolution of dual mutants.
“Additional changes may further affect susceptibility to antiviral drugs or provide a competitive advantage over circulating wild-type viruses.”
More than 35 million people fell ill with the flu during last year’s season, while 390,000 were hospitalized with the disease and 24,000 died, according to estimates.