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    Archived 19 October 2017

    Influenza is a potentially life-threatening virus that spreads quickly from person to person. It is a significant public health issue in this country, with 10–20 percent of New Zealanders infected every year. While influenza outbreaks can occur all year round, rates peak in winter and spring. This is because the virus can survive longer outside the body in periods of colder weather and low absolute humidity (dry conditions).

    We classified Influenza as supporting information.

    Key findings

    In 2013, 88 percent (687 of 782) of influenza hospitalisations in New Zealand occurred during the winter and spring months from mid-June to early November.

    • Influenza hospitalisations peaked in September 2013, with 67 influenza hospital discharges in the first and second weeks of the month (weeks 36 and 37).
    • In 2000–13, an average of 578 hospitalisations per year were related to influenza. From 2000–11, this resulted in an average of 17 deaths per year.
    • In 2009, 1,484 hospitalisations and 49 deaths were from influenza. The Ministry of Health stated that 1,122 of these hospitalisations and 35 deaths were caused by the Influenza A (H1N1) pandemic, commonly referred to as swine flu.

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    Figure 2

    Definition and methodology

    These data are based on Ministry of Health data for publicly funded hospital discharges. They are collected under the National Minimum Dataset (hospital events) and reported in an annual surveillance report by the Institute of Environmental Science and Research (ESR).

    The survival and transmission of the influenza virus decreases in high humidity (Tompkins et al, 2012). Warmer-than-normal temperatures and higher-than-normal humidity during the months of winter and spring may result in reduced annual influenza rates. This is reflected in the climate-change health risks for influenza modelled as part of ESR’s Health Analysis and Information for Action (HAIFA) project.

    However, influenza infection is determined by other factors besides temperature and humidity. Influenza outbreaks can occur all year round, and factors such as vaccination coverage are likely to influence infection rates.

    Data quality

    We classified Influenza as supporting information.


    This supporting information is an indirect measure of the ‘Acute health effects related to our changing climate’ topic.


    The accuracy of the data source is of high quality.

    See Data quality information for more detail.


    Environmental Science and Research (2014). Health Analysis and Information for Action (HAIFA). Available from

    Tompkins, D, Brock, A, Jones, G, McBride, G, Tait, A, Benschop, … Slaney, D (2012). Modelling the impacts of climate change on infectious diseases in New Zealand. Prepared by the Institute of Environmental Science and Research with NIWA, Landcare Research, and Massey and Waikato Universities. Available from


    Published 21 October 2015

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