Most parents skip the flu jab for their children. Is that a bad idea?

Sydney Morning Herald

21 hours ago

The bulk of influenza infections occur in children; they are also the main transmitters of the virus within the community. One study of 29 countries, including Australia, found 19 per cent of flu cases were in children under four.
Consider this study from Hong Kong that tracked the spread of flu through households: kids under 18 were up to 2.8 times more likely to pass on the virus than adults, and they were more likely to catch it. Children seem to shed more copies of the virus (including before they show symptoms); they also tend to have closer contact with adults. They are also less likely to wash their hands, and more likely to put things in their mouth.
Why? Principally because they are immune-naive: their bodies have not had time to train on influenza. An adult has an arsenal of antibodies to several different strains of the flu. A young child has nothing beyond any left-over antibodies from their mother.
'They are new in the world, and they are getting infected with a lot of different viruses,' says Professor Kristine Macartney, director of the National Centre for Immunisation Research and Surveillance.
'While that's inevitable, what we don't want – and I promise you as a paediatrician who has cared for many kids critically ill in hospital with flu – we don't want to see kids with severe illness.'
We often think of the flu as a nuisance for young people and adults, and a threat for the elderly. Consider flu vaccination rates: 60 per cent of Australians over 65 have had a jab, compared to 24.7 per cent of those under five.
'They are new in the world, and they are getting infected with a lot of different viruses.'
Professor Kristine Macartney on the susceptibility of children
But influenza hospitalisation rates among very young children are surprisingly high – higher still if you add in all those who have co-infections, such as RSV at the same time.
Young children also tend to suffer the most from the flu. They typically have higher fevers, more severe symptoms, and shed more of the virus, which explains why they are such effective transmitters.
Indeed, every year the flu kills about 250,000 to 500,000 people globally, including about 28,000 people under 18.
Some years, the hospitalisation rate for Australians under five exceeds that of those over 65. And while children with comorbidities are particularly at risk, there does seem to be a lot of random variation, with some perfectly healthy youngsters getting severely ill and ending up in intensive care.
'The vast majority of kids we see hospitalised each year … are healthy children. When this happens, it is a shock to parents,' Macartney says.
Per the most recent Australian influenza season report, 39 people died with the flu in sentinel hospitals (those participating in influenza surveillance) in 2023, nine of them children.
When we are infected, or vaccinated, our bodies develop armies of antibodies specific to glycoproteins on the surface of the virus.
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Over time, and under pressure from our new antibodies, the virus mutates – a process known as antigenic drift – eventually to the point where our antibodies no longer recognise it. We undergo another cycle of infection and immunity.
Remarkably, antibodies developed to a flu infection in childhood may actually offer us lifelong protection against similar strains of flu, a process known as immune imprinting.
Australia licenses two free vaccines for children under five. Unlike the adult vaccine, they are given over two doses.
Vaccinating kids for the flu seems to work reasonably well. A large US study in 2020 found having at least one dose of vaccine cut the chances of hospitalisation from the flu by 55 per cent.
'So it's good, but it's not great,' says Professor Robert Booy, an infectious diseases paediatrician at the University of Sydney, who has run clinical trials of flu vaccines. The overall reduction in infections tends to sit at about 50 to 60 per cent, he says.
There are also community benefits. Vaccinating children seems to cut the amount of virus that is spread around the community. Given the number of viruses parents have to endure from their children, avoiding one seems a smart bet.
And the vaccine seems safe. Australia conducted one of the phase 3 trials for one of our vaccines licensed in children. It reported zero serious adverse events or deaths. Just 1.1 per cent of parents take their children to see a doctor in the days after getting a flu shot.
Given all this, why are flu vaccination rates falling among kids?
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The obvious answer is: the pandemic. During 2020, parents wanted to protect their kids from COVID, but there was no COVID vaccine, so they got a flu jab instead. 'People were trying to take action against something,' says Jessica Kaufman, head of the vaccine social science team at the Murdoch Children's Research Institute.
After COVID was no longer front of mind, parents began putting less emphasis on the importance of flu protection. Parents are busy as it is without one more thing to think about – and kids don't much like having needles stuck in their arms.
The flu vaccine is optional, compared to the more stringently recommended vaccines of childhood. Perhaps some parents worry about over-jabbing their kids?
But the world is full of antigens, Booy says. Adding one more is not going to make much of a difference.
'It's a vaccine that is completely safe. It absolutely helps benefit not only the child, but also the immediate family and everyone around them. Children are super-spreaders,' Macartney says.
'It is definitely not too late to vaccinate. We have influenza on the rise at the moment – it's looking to be well above previous years.'