In November 2009, the Norwegian Institute of Public Health reported the finding of a specific mutation in virus from three pandemic influenza patients with fatal or severe disease. The mutation was not found in the 70 viruses from mild cases that had been analysed at the time. The World Health Organization was notified of the finding. Subsequent to these initial findings, the investigation has continued and expanded analysis of viruses from 266 patients has now (March 4, 2010) been published as a Rapid Communication in the journal Eurosurveillance.
The initially observed pattern and the early assessment are supported by the new, expanded analysis.
The mutation (denoted D222G, in the viral HA glycoprotein) are still found only in patients with severe illness (in 11 out of 61 severe/fatal cases). It has not been found in any of the 205 analysed cases with mild disease. This lends good support for an association between the mutation and a severe clinical outcome.
While this is in good agreement with the hypothesis that the mutation increases the pathogenicity of the virus, the analysis does not prove a cause-and-effect relationship.
- We still need to know what effect, if any, this mutation has on the biological characteristics of the virus, says Olav Hungnes, senior scientist and head of the national influenza laboratory at the Norwegian Institute of Public Health.
- However, we do know that the change occurs in the part of the virus that is responsible for binding to and infecting the cell. It is quite possible that the mutation helps the virus to infect a wider range of cells in the lower respiratory tract and thus lead to more severe disease, he says.
- But clearly, non-mutated viruses are also in rare cases capable of causing severe disease. In the majority of severe and fatal cases studied, this mutation was not found. Other characteristics of the virus, as well as risk conditions in the person who is infected, must come into play.
This mutation has been found sporadically throughout the period of pandemic virus circulation, since the first severe and fatal cases in the summer. There is no indication that the mutated virus has increased in frequency during this period.
- Viruses carrying this mutation do not seem to be circulating in the population, it rather looks like it is a sporadic and spontaneous change that occurs in single infected people and rarely is carried onwards to others. If this is the case, it probably means that these viruses are less contagious. Chances are then minimal for them to emerge in large numbers and their significance in a public health perspective is limited, says Dr. Hungnes.
- Nonetheless, this finding of mutant viruses that could possibly be more aggressive, serves as a reminder that the generally mild nature of the current pandemic virus may not be unchangeable, There is no reason to be complacent in carrying out measures that limit infection with this virus, concludes the Norwegian scientist.
The possible significance of this and other mutations that may alter the virulence and transmissibility of the pandemic influenza A (H1N1) virus continue to be closely monitored and investigated by scientists in Norway and elsewhere.