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Vaccines do work for pandemic flu

Vaccine against swine flu in 2009 prevented infections and hospitalisations

Ingrid Torjesen

Tuesday, 14 March 2017

Vaccines are successful in preventing pandemic flu and reducing the number of patients hospitalised as a result of the illness, researchers at the University of Nottingham have found.

However, the research* - the most comprehensive review undertaken in this area - also found that the effectiveness of vaccines can vary depending on the age of the patient.

In early 2009, a novel influenza A(H1N1) virus or 'swine flu' appeared in humans, containing a unique combination of influenza genes which had not previously been identified in animals or people. The first cases were reported in the United States in March 2009 and the new virus spread rapidly to other countries prompting the World Health Organization to declare a pandemic in June 2009. An estimated 61 million people were infected worldwide.

Vaccines against the new strain were developed and rolled out across the world from September to December 2009. The majority of vaccines available contained inactivated A(H1N1)pdm09 influenza virus rather than live virus. Some formulations also contained an adjuvant to strengthen the body's immune response to the vaccine and allow smaller doses of antigen to be used.

Many individual studies have looked at how effective the available vaccines were at preventing illness and hospitalisation caused by the pandemic influenza strain but up until now no-one had summarised all the available data.

For this systematic review and meta-analysis, the researchers identified 38 studies published between June 2011 and April 2016 that measured the effectiveness of the inactivated pandemic influenza vaccines, covering a population of more than 7.6 million people. Twenty-three of these studies reported results that were suitable for inclusion meta-analysis.

The results, published in the journal Vaccine, showed that pandemic influenza vaccines produced globally during the 2009-10 pandemic were largely effective in reducing illness and hospitalisations, and adjuvanted vaccines tended to be more effective than non-adjuvanted vaccines but only in children.

Pandemic influenza vaccines were found to be 73% effective at preventing laboratory-confirmed influenza illness and 61% effective at preventing hospitalisation in the population as a whole. However, when the vaccines' effectiveness was examined in different age groups, they were shown to be less effective in adults over 18 years than in children, and effectiveness was lowest in adults over 50 years of age. Adjuvanted vaccines in particular were found to be more effective in children than in adults against laboratory confirmed illness (88% in children versus 40% in adults) and hospitalisation (86% in children versus 48% in adults). The lower effectiveness in older people may be due to them having pre-existing antibodies against A(H1N1)pdm09 from previous exposure to a similar virus, with corresponding lower incidence of the infection in this age group, the researchers suggested.

Professor Jonathan Van Tam, who led the research conducted by the University's Health Protection and Influenza Research Group in collaboration with other scientists in the UK, Japan, Bosnia and the Netherlands, said: "The 2009 swine flu pandemic was the first in human history when pandemic vaccines have been available worldwide. It's therefore really important to pull all of these data together and ask the question: did these vaccines really work?

"We found that the vaccines produced against the swine flu pandemic in 2009 were very effective in both preventing influenza infection and reducing the chances of hospital admission due to flu. This is all very encouraging in case we encounter a future pandemic, perhaps one that is more severe. Of course, we recognise that it took five to six months for pandemic vaccines to be ready in large quantities; this was a separate problem. However, if we can speed up vaccine production times, we would have a very effective strategy to reduce the impact of a future flu pandemic."

* Lansburya LE, Smitha S, Beyer W, et al. Effectiveness of 2009 pandemic influenza A(H1N1) vaccines: A systematic review and meta-analysis. Vaccine, published online 14 March 2017. DOI: 10.1016/j.vaccine.2017.02.059

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