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Influenza vaccination in kids

9th Aug 2011
Professor Dominic Fitzgerald   all articles by this author

Should we routinely immunise preschoolers against influenza?

Influenza is one of the most common reasons for young children to present to hospital and to be admitted.

Primarily this occurs for investigation and management of fever with coryzal symptoms but also includes other presentations such as viral-induced wheezing, asthma, bronchiolitis, pneumonia and croup.

In fact, it has been established that asthma, and in particular the viral-induced wheezing phenotype in the preschool age, is one of the most common chronic underlying medical conditions in children.

Children with asthma have a higher rate of hospitalisation than children without asthma when they have influenza.

Moreover, the cost of the care of children with influenza virus infection is likely to be many hundreds of millions of dollars annually.

A recent report, by Dawood and colleagues from the US Centers for Disease Control and Prevention, examined the demographics of children with asthma who required hospitalisation with seasonal influenza (influenza A or B) or pandemic influenza A (H1N1) between 2003 and 2009.

Approximately 32% of children (aged over two years) hospitalised with asthma in this study had seasonal influenza, but the proportion rose to 44% during 2009 with the H1N1 pandemic influenza strain.

With the pandemic strain in 2009, statistically significantly more children than in earlier years required admission to intensive care (22% vs 16%), more developed pneumonia (46% vs 40%), but equal proportions developed respiratory failure (5%) or died (1%).

Interestingly, significantly more children with influenza A (seasonal or pandemic) had diagnoses of asthma exacerbations than those with influenza B (51% vs 29%).

The study confirmed other studies that have shown that all influenza has a high burden for young children and especially those with asthma who are more likely to be hospitalised in the preschool years.

It is now clear that the pandemic influenza H1N1 was not the dreaded infection it was first feared for children. It has emerged somewhat unexpectedly that pregnant women were disproportionately more severely compromised by their infection.

This has been attributed to their relative immune compromise (to avoid rejection of their fetus) during pregnancy, which made them somehow more susceptible to pandemic influenza infection.

Obviously, the interplay between infected young children and their mothers is of importance with the high rates of transmission of the H1N1 virus.

As we reflect upon the consequences of the H1N1 pandemic for children, there is an opportunity to think more broadly about the role of influenza immunisation in young children.

Vaccination against influenza is available for children six months of age and older in Australia, and is recommended for Indigenous children and those children with chronic cardiac and respiratory conditions.

Since the H1N1 pandemic, broader uptake for the vaccination has been actively encouraged by medical authorities.

However, the uptake rate for children in Australia is currently around 10%.

The uptake has been less than anticipated for several reasons, including limited access to the vaccine for those who may benefit most, delivery of vaccine in multidose vials and side-effects of one vaccine brand.

Perhaps with better implementation strategies, these factors can be overcome.

Preschool children, and the elderly who are already advised to be vaccinated, are 3–4 times more likely than people aged 5–65 years of age to be hospitalised with influenza, based on data from WA (data courtesy of Professor Peter McIntyre, NCIRS).

It may be time to consider broadening the vaccination schedule to include all preschool children as well as the elderly.

Who knows, an initiative to improve the health of children, which will protect adults, may also prove cost effective.

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