OSLO (Reuters) - Norwegian health authorities said on Friday they have discovered a potentially significant mutation in the H1N1 influenza strain that could be responsible for causing the severest symptoms among those infected.
"The mutation could be affecting the virus' ability to go deeper into the respiratory system, thus causing more serious illness," the Norwegian Institute of Public Health said in a statement.
Authorities added they had no reason to believe the mutation had any implication for the effect of flu vaccines or antiviral drugs made by groups such as Roche, GlaxoSmithKline, Novartis or AstraZeneca.
H1N1, a mixture of swine, bird and human viruses, has killed more than 7,000 people globally.
In Norway the mutation was found in the bodies of two people killed by the virus and of one person made seriously ill.
The two people infected by the mutated virus were among the first fatalities from the H1N1 pandemic in Norway, the institute said.
It was unclear whether the mutated virus was transmitted among humans, the health authorities said.
"Based on what we know so far, it doesn't seem like the mutated virus is circulating in the population, but rather that spontaneous changes have happened in the three patients," director Geir Stene Larsen at the public health institute said in the statement.
In some later fatalities linked to H1N1 that were studied, the same mutation was not found. It had found other mutations in some other cases, but the mutations found in two of the first fatalities and one seriously ill patient had been of "particular interest", it said.
Norway has seen relatively more fatalities in the flu pandemic compared to the size of the population versus other European countries, with 23 confirmed deaths.
Public health authorities have said this could be due to the country being hit early in the pandemic's northern hemisphere winter wave, before a mass vaccination programme got underway.
"Nevertheless, it is important to study if there's still something about the Norwegian fatalities that separate us from other countries, and that make us learn something that strengthens our treatment of the seriously ill," director Bjorn-Inge Larsen at the Norwegian Directorate of Health said.