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Paradigm Shift Intervention Monitoring
Of 336 influenza H1N1 (2009) viruses reported as tested for antiviral susceptibility at RVU (not including regional labs) since week 40 2010, six have been found to carry the H275Y mutation which confers resistance to the antiviral drug oseltamivir.
The above comments are from the HPA influenza report for week 52. In the week 51 report there were three cases out of 402. The drop in the number tested was due to the exclusion of data from regional labs, suggesting that the number of sequences with H274Y was higher than the six at RVU. This rise in cases with resistance raises concerns that the trend will continue and expand as Tamiflu use becomes more widespread. H274Y is widely circulating as a minor sub-population, which is more easily seen in samples collected after the start of treatment. The emergence of H274Y can have a significant effect on the number of severe and fatal cases, which will increase the strain on ICU beds and ECMO machines.
The increase in H274Y effects will led to an increased use of Relenza, zanamivir. However, resistance to Relenza has also been reported, and sequential use of Tamiflu and Relenza will likely lead to an increase in resistance to both neuraminidase inhibitors.
The resistance level for the adamantines is already hear 100%, raising concerns that all approved antivirals may be of limited value, as the number of cases expands.