Several strains of influenza A H1N1 that are more resistant to a primary flu drug have emerged in the United States, scientists with the U.S. Centers for Disease Control and Prevention (CDC) have reported.
The strains, which contain mutations called I223V and S247N, have been detected in countries across five continents, including the United States.
CDC scientists working with the strains in laboratories found Tamiflu, the influenza drug, was up to 16 times less effective against the mutated strains, according to a study the agency published on June 12. At the same time, three other drugs that were tested worked well against the strains.
“These mutated viruses retained sensitivity to other anti-influenza medications, including a newer one, baloxavir marboxil. There are no immediate implications to change decisions for clinical care,” a CDC spokesperson told The Epoch Times in an email.
The CDC noted that some other strains were even more resistant to Tamiflu, or oseltamivir. One with a mutation called H275Y, for instance, reduced the effect of Tamiflu by up to 1,000 times in laboratory testing.
Eleven samples carrying I223V, S247N, or both were collected from the United States, along with two H275Y samples, by the researchers who carried out the new study. Other countries from which samples showed the mutations included Bangladesh, Niger, and Abu Dhabi.
The scientists said that analysis of the viruses with mutations showed they’ve been circulating globally since May 2023 and were only detected in 0.67 percent of samples collected from various countries.
“However, those data may not necessarily represent the actual proportion of what was in circulation because of differences in surveillance and sequencing strategies in each country,” Dr. Mira Patel, one of the CDC scientists, and her co-authors wrote.
Hong Kong scientists reported on the mutations previously, saying in a different paper that analysis of data from a global repository showed the prevalence of cases caused by the strains with I223V or S247N mutations increased in the fall of 2023. Those researchers also concluded, based on testing, that the mutations showed more resistance to oseltamivir and another drug, zanamivir.
The viruses with both mutants were described as dual mutants.
H1N1 is an influenza virus. commonly known as the swine flu. It’s different from H5N1, or the bird flu, which has been circulating in cows and other animals in the United States.
The CDC scientists said that the rapid spread of the dual H1N1 mutants to countries across multiple continents “suggests no substantial loss in their replicative fitness and transmissibility.”
“It is unknown how widely these mutated viruses will circulate in the upcoming season,” the CDC spokeswoman said. “It is important to continue monitoring the spread of these viruses and the evolution of these viruses as they may acquire other mutations that could further impact the usefulness of oseltamivir or other antiviral medications.”