When we think of vaccination, we generally think of children because that is when we usually get immunised. With COVID-19, it is a different story, because the push is to vaccinate adults before kids.
“The need to vaccinate kids is fairly limited,” says Associate Professor Paul Griffin, an infectious diseases physician and microbiologist at The University of Queensland and director of Infectious Diseases at Mater Research.
Unlike other respiratory viruses such as influenza, children have a minimal risk of developing severe COVID-19 infection, and deaths are rare. They also don’t seem to contribute to transmission significantly.
Initially, COVID-19 vaccine development targeted adults because the virus affects people more as they get older. But as the adult population is immunised, children’s contribution to the transmission might become increasingly significant.
Evidence that vaccines might reduce transmission of SARS-CoV-2 is building up, so vaccinating children could have beneficial knock-on effects on the broader community.
Griffin says it would be ideal to have everybody vaccinated, and it would be sensible to include older children in the vaccination planning. But children remain at the lowest on the list of priorities.
“The reason why they are behind the rest of the population is not that we anticipate safety concerns or reduced efficacy,” he says. “It was identified fairly early that children are much less likely to contribute to the pandemic, there are far lower risks of progressing to more significant disease, and it’s more difficult from an ethical standpoint.”
One of the main challenges in running a paediatric clinical trial is that children can’t provide consent. Their carers must provide it for them.
“There are dilemmas around what age we allow children to consent for themselves, whether there’s coercion from parents. It’s just much more ethically challenging, and it takes longer.”
Pfizer had included 16- and 17-year-old children in their initial trials. At the beginning of this year, both Pfizer and Moderna commenced trials on younger children – 12 and older. These trials resemble those done in adults. Children are given two standard doses.
Early results show that 12- to 15-year-old children develop substantially higher levels of antibodies than 16- to 25-year-olds in earlier trials.
But trials in children younger than 12 are different.
While safety is a crucial part of any clinical trial, it is paramount in children, especially when testing a vaccine for a disease that does not severely affect them.
Firstly, scientists need to figure out what dose gives the highest protection with minimum adverse effects. Once the safe dose is established, the second part of the trials involves immunising a few thousand children and following them to look out for signs of COVID-19 infection.
Because children are often asymptomatic, researchers will be looking at immune markers in their blood. These trials will likely show that vaccines trigger a strong immune response in children, but demonstrating that they prevent disease or block transmission might be more complicated.
AstraZeneca and Johnson & Johnson have temporarily paused trials in children while they continue to investigate the occurrence of rare blood clots in vaccinated people.
“The prioritisation of clinical trials in children would have been different had they contributed much more to the spread of this virus,” says Prof Griffin.
“The relative benefits-versus-risk ratio is different for almost every individual, and certainly, as we look at a younger age where the risks of more severe disease are similar to that of the vaccine, then that risk/benefit equation does need to be factored in.”
“That’s why we’ve left them to the end so that we don’t embark on any clinical trials in children with any vaccines that don’t have ample safety data.”