Influenza and norovirus forecasts - expert responds

Influenza and norovirus forecasts - expert responds

16 January 2013
Not one, but two infectious diseases have been raising concerns among New Zealand experts as they prepare for the 2013 winter season.

A strain of H3N2 influenza virus is currently causing high levels of hospitalisations in the northern hemisphere, reaching epidemic proportions in the US and linked to over 20 child deaths there so far this season.

Researchers have separately expressed concern about a global outbreak of norovirus, linked to a new variant of the Sydney 2012 strain, that is already causing problems in New Zealand and expected to continue.

Additional resources:
Behind the Headlines fact sheet on the current norovirus outbreak
MPI's Food Smart norovirus resource page

World Health Organisation (WHO)'s latest influenza update
US Center for Disease Control (CDC) press briefing on current flu season's vaccine effectiveness

The Science Media Centre gathered the following comments from expert virologist Dr Sue Huang, Director of the WHO National Influenza Centre at the Institute of Environmental Science and Research Ltd (ESR).

Dr Huang's responses to the SMC's questions are listed below:

What are the concerns about H3N2 strain and how likely is the virus to cause problems in NZ this winter?
"A(H3N2) is a concern, in particular for very old and very young populations. We need to monitor the situation closely. The H3N2 strain* causing high level of hospitalisations in USA, especially in New York, may potentially cause problems for NZ's coming winter."

*known more formally as the A/Victoria/361/2011-like strain

Vaccine coverage is reputed to be imperfect in the US even though this was an identified strain and included in the season's influenza vaccine. Will NZ potentially face the same issue?

"The latest information I have received from the WHO indicates that A(H3N2) viruses circulating since September 2012 produce antigens similar to the Victoria strain seen last winter in NZ. The majority of the most recently analysed viruses also belong to the same genetic group as the A(H3N2) viruses we experienced in NZ's past winter.

"My personal view about the situation in northern hemisphere countries is that it is not arising because the vaccine is not well matched with the current circulating viruses. It is about vaccine uptake, which is not optimal, and the fact that there are more susceptible populations to H3N2 infections, due to two years dominated by the H1N1 strain of influenza globally."

Putting the norovirus and influenza outbreaks in context -- which is more worrying to health officials in terms of likely burden on the health system, potential fatalities and other factors?

"Both viruses can add substantial burden to our health systems. However, in general, influenza-associated complications can cause much higher hospitalisations and mortality each winter, particularly for very young and very old people, and people with underlying medical conditions."

ENDS

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