Study finds influenza viruses put more people in hospital

Study finds influenza viruses put more people in hospital than last year

Preliminary findings from the third year of a multi-million dollar five-year international flu study reveal high numbers of people were hospitalised with severe acute respiratory illness (SARI) caused by influenza viruses.

2014 figures from The Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance study (SHIVERS) show Intensive Care Unit (ICU) admissions for patients with SARI and influenza were twice as high as those for the 2013 winter season.

Over the 2014 New Zealand winter, flu experts led by SHIVERS Principal Investigator, Dr Sue Huang from the Institute of Environmental and Science Research (ESR) have tracked the ever-changing influenza viruses through patients admitted to Auckland District Health Board and Counties Manukau District Health Board hospitals with severe acute respiratory illness and those who sought GP consultations with influenza-like illness (ILI).

The rate of influenza hospitalizations in Central, East and South Auckland in 2014 (37.4/100,000) was higher than in 2013 (28.7/100,000). The numbers of patients admitted to ICU with SARI (91) and influenza (18) in 2014 were twice as high as ICU patients with SARI (44) and influenza (8) in 2013.

Four patients died of influenza A(H1N1)pdm09 in 2014 compared with none in 2013.

Infants under one were hardest hit with the highest influenza hospitalisation rate (348/100,000), a rate almost five times higher than children aged 1-4 years (66/100,000), the second hardest hit age group.

The rate of general practice consultations with influenza-like illness during 2014 (1.4%) was similar to 2013 (1.6%).

Among all ages, children aged 1-4 years had the highest influenza-related consultations. This is different from 2013 when children aged 5-19 years had the highest rate.

A(H1N1)pdm09 was predominant in Auckland and NZ, consisting of 60 percent of all influenza viruses and 85 percent of all typed viruses.

Dr Huang said these preliminary findings provided insights into the differential effect of the virus strain on various age groups who were admitted to hospitals or visited GPs.

“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 populations each year and identifying those vulnerable subpopulations so we can better protect them through use the right vaccines, vaccine strategies and effective care for those who do get the flu,” Dr Huang said.

One of the areas being looked at by the SHIVERS team is the effectiveness of the flu vaccine.

The study found that when averaged across all ages, the whole 2014 vaccine provided 67 percent protection against influenza that leads to a visit to a general practice and 54 percent against influenza that leads to hospitalisation.

The individual A(H1N1)pdm09 strain of the 2014 vaccine matched well with the predominant circulating strain, with the vaccine giving good protection at around 73 percent against general practice consultations and 65 percent against influenza hospitalisations.

Director of the Immunisation Advisory Centre (IMAC), The University of Auckland and co-lead of SHIVERS, Associate Professor Nikki Turner, says this year the study highlighted the value of timely assessment of vaccine effectiveness (VE).

“We were pleased that the SHIVERS results were able to be provided to the World Health Organization (WHO) vaccine strain selection committee to support decision-making for the recommendations on the influenza vaccine strains to be used in Southern Hemisphere countries for the following year,” Dr Turner said.

The A(H3N2) and B viruses were much less common during the 2014 winter season, however, these viruses have shown some small genetic changes

In response to this the virus strains used for the influenza vaccine have been updated to match what is forecast to be circulating during 2015. This is based on WHO’s recommendation which has been accepted by all Southern Hemisphere countries, including New Zealand. The vaccine virus strains are:
• A/California/7/2009 (H1N1)pdm09-like virus
• A/Switzerland/9715293/2013 (H3N2)-like virus
• B/Phuket/3037/2013-like virus.

The New Zealand flu experts involved in the SHIVERS study are briefing their international colleagues from the US Centers for Disease Control and Prevention (CDC) and St Jude Children’s Research Hospital in Memphis, Tennessee, on the 2014 results from 2014, over two days (10-11 November) in a meeting at the University of Auckland.

CDC has provided full funding of US$1.5m for the fourth year of the SHIVERS project.

Dr Huang says the funding shows international confidence in the New Zealand health system and the results produced through a strong collaboration among scientists, researchers, clinicians, hospitals, sentinel general practices.

The funding in year four (2015) will enable the SHIVERS team to conduct a serological survey of people in the community in addition to the current SARI and ILI surveillance platforms.

Dr Huang said the survey will allow a better understanding of the full range of the disease burden from asymptomatic infection, symptomatic infection, mild illness that does not end up needing general practice intervention, moderate disease seeking general practice consultations and severe illness resulting in hospitalisations.

“Influenza-related hospitalisations and general practice consultations are the ‘tip of the iceberg’

"Extending the study to include a serological survey will provide further insight into the full impact of the influenza virus on the health and well-being of the community,” Dr Huang said.

Summary of preliminary findings
• High numbers of people hospitalised with respiratory illness tested positive for infection with influenza viruses in the winter flu season this year. The numbers of patients admitted to ICU with severe acute respiratory illness and influenza infections almost doubled compared to last year
• Infants under one are hardest hit with the highest rate of influenza hospitalisations.
• Children under four have the highest rate of influenza-related general practice visits.
• In New Zealand, the pandemic virus A(H1N1)pdm09 predominated for most of the winter season in 2014.
• The 2014 vaccine provided reasonable protection against hospitalisation or visiting a general practice with influenza.
• These findings support of the importance of the annual national influenza immunisation programme, particularly to protect those most vulnerable to the effects of influenza.

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Background
The Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance (SHIVERS) study is investigating five winter ‘flu seasons’ amongst the Auckland population. The study led by ESR in New Zealand is a multi-agency collaboration between ESR, Auckland District Health Board (ADHB), Counties Manukau District Health Board (CMDHB), The University of Auckland, University of Otago, the US Centers for Disease Control and Prevention (CDC) and the WHO Influenza Collaborating Centre at St Jude Children’s Hospital in Memphis, USA as well as Primary Health Organisations, sentinel general practices and Auckland Regional Public Health Services.

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

For more information on the SHIVERS project go to www.esr.cri.nz

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