NZ flu study finds influenza viruses put more people in hospital than was previously thought

06 November 2012
SHIVERS Study 2012: Overview of preliminary findings

SHIVERS InfographicHigh numbers of people hospitalised with respiratory illness tested positive for infection with influenza viruses.

Children under four hardest hit with highest rate of influenza hospitalisation.

High rates of influenza hospitalisations in people older than 80 years were identified.

Pacific Island and Maori populations had highest rate of hospitalisation from influenza (by ethnic group).

In Auckland, swine flu pandemic A(H1N1) viruses predominated during June and July and then A(H3N2) viruses predominated during August and September.

A(H3N2) viruses were predominant across the rest of New Zealand from June through to September.

If the Northern Hemisphere follows the same pattern found during the 2012 NZ winter with A(H3N2) viruses predominating, then influenza hospitalisation rates, particularly for the very old and very young, may be substantial.

These findings support the boosting of vaccination rates in the community to protect those most vulnerable to the effects of influenza.

The influenza viruses circulating in New Zealand changed throughout the winter period (April to September 2012) and new vaccine strains have been selected to better match currently circulating viruses.

There were substantial numbers of people hospitalised with severe acute respiratory infections caused by other respiratory viruses.

Preliminary findings from the first full year of a multi-million dollar five-year international flu study led by ESR in New Zealand have shown more people are hospitalised with severe acute respiratory infections (SARI) caused by influenza viruses than previously thought.

The Southern Hemisphere Influenza Vaccine Effectiveness Research and Surveillance (SHIVERS) study is investigating five autumn and winter 'flu seasons' amongst the Auckland population. The study is a multi-centre collaboration between ESR, Auckland District Health Board (ADHB), Counties Manukau District Health Board (CMDHB), University of Otago, University of Auckland, the US Centers for Disease Control and Prevention (CDC) and the WHO Influenza Collaborating Centre at St Jude Children's Hospital in Memphis, USA.

The SHIVERS team is building on New Zealand's world leading influenza surveillance systems, which track viruses in real time using data from hospitals and general practitioners (GPs) working in the community.

Over the 2012 New Zealand winter, flu experts led by the SHIVERS Principal Investigator, Dr Sue Huang from ESR, have tracked the ever-changing viruses through patients admitted to ADHB and CMDHB hospitals with influenza-related SARI.

The rate of influenza hospitalisations during the 2012 flu season was the fourth highest recorded over the past twelve  years, with children under four years and the elderly being the hardest hit.

From 30 April 2012 to 2 September 2012 a total of 1,370 SARI cases was recorded, including 38 intensive care unit (ICU) admissions and seven deaths. Infants aged younger than one year had the highest influenza hospitalisation rate of 228.7 per 100,000 age group population. This was followed by people aged 80 and older (128.6 per 100,000), people aged 65-79 years (81.1 per 100,000) and children aged one to four years (54.9 per 100 000).

Dr Sue Huang said although the findings are preliminary, discovering an increased burden from  influenza viruses than previously thought shows the need for countries to work together on the best ways to prevent and manage influenza.

"Influenza causes more illness each year than any other vaccine-preventable illness. This study highlights the importance of tracking the viruses which cause influenza across the population so we can better protect against them through the right vaccines, prevent their  spread and care for those who do get the flu."

One of the areas being looked at by the SHIVERS team is the effectiveness of the flu vaccine. Dr Nikki Turner, Director of the Immunisation Advisory Centre (IMAC), University of Auckland, says this year the study looked at the effectiveness of the vaccine in preventing hospitalisation from flu. "To date, the data is incomplete, so we do not as yet have a very accurate measure for the effectiveness of the vaccine.  However, we will continue to collect data over the next four years.

"In the next year of the SHIVERS study we will also look at patients with influenza presenting to general practice. This means that in future years the study will be able to measure how effective the vaccine is in preventing flu related GP consultations and hospitalisations."

Dr Adrian Trenholme, a paediatrician at Middlemore Hospital says that young children aged  less  than four years are hit hardest by influenza viruses, so getting a flu shot is important to protect them.

"The SHIVERS study has shown a previously under-recognised burden of non-influenza respiratory viruses causing substantial hospitalisations, particularly in young children."

Dr Sally Roberts, Clinical Head of Microbiology at Auckland City Hospital says that SARI surveillance also showed that the most prevalent influenza viruses identified among patients in Auckland this year were different from the rest of the country.

"During June and July, the swine flu pandemic A(H1N1) viruses were predominant in Auckland, but then there was a switch to A(H3N2) predominance in August and September. Whereas, A(H3N2) viruses predominated throughout the winter season for the rest of New Zealand."

The virus strains used for the influenza vaccine have been updated to match what is forecast to be circulating during 2013. This is based on the World Health Organisation's recommendation which has been accepted by Southern Hemisphere Countries, including New Zealand.  The vaccine virus strains are:

    A/California/7/2009 (H1N1)-like virus
    A/Victoria/361/2011 (H3N2)-like virus
    B/Wisconsin/1/2010-like virus.

The New Zealand flu experts involved in the SHIVERS study are briefing their international colleagues from the CDC and St Jude Children's Research Hospital in Memphis, Tennessee, over the next two days in Auckland.

Continued:

http://www.nzdoctor.co.nz/un-doctored/2012/november-2012/06/nz-flu-study-finds-influenza-viruses-put-more-people-in-hospital-than-was-previously-thought.aspx