A surge of COVID-19 cases among young children and teenagers means vaccinating children could offer them direct protection and help the whole community get closer to herd immunity.
Is it necessary to vaccinate young children?
SARS-CoV-2 is much less likely to cause serious illness in children than it is in adults. But some children do become very ill.
The spread of the highly infectious Delta variant has seen children infected at higher rates. The UK and the US are recording an increasing number of cases and hospitalisations among children. In NSW, children and teenagers have counted for more than one-third of all cases in the past two weeks, with several outbreaks occurring in childcare centres.
Concerns about transmission by children and adolescents are also growing as the adult population is increasingly immunised and more infectious strains emerge, making herd immunity an even more elusive target.
The increased ability of the Delta variant to infect children is evident, and it justifies the need for vaccinating them, says Associate Professor Paul Griffin, an infectious diseases physician and microbiologist at the University of Queensland and director of Infectious Diseases at Mater Research. He points out that the benefit of vaccination in children goes beyond protecting them from the virus. It would allow them to return to school and socialise with their peers safely.
Griffin says that eventually, we will have to vaccinate children routinely to address the pandemic.
“Children can definitely be infected and definitely pass it on,” he says. “We won’t be able to contain this virus to measurable levels if we don’t include children in that routine vaccination schedule.
“But we don’t vaccinate them only for the impact on others. They definitely need to be protected themselves to allow them to move around freely and attend school, [the] impact [of which] on their development is tremendous.”
But not everyone agrees COVID-19 vaccines offer a direct benefit to children right now.
Associate Professor Asha Bowen, a paediatrician at Perth Children’s Hospital and head of Skin Health at the Wesfarmers Centre of Vaccines and Infectious Diseases at the Telethon Kids Institute, says the increased transmissibility of the Delta variant has not changed the clinical outcome of the infection in children. Whether it will be necessary to vaccinate children, she says, will depend on how the pandemic evolves and whether the infection will increasingly affect children.
“Throughout this pandemic, we have seen that children are not getting as sick as adults, don’t need to be hospitalized and don’t get admitted to ICU as much as adults,” Bowen says. “Today, we can’t easily see the direct benefits for children to be vaccinated.”
Nonetheless, Bowen says we don’t fully understand how the pandemic will play out in the future and running COVID-19 vaccine trials on young children “prepares the way for a greater understanding of what might be needed for children [in the future].”
How are vaccine trials done in young children?
Before any clinical trial in humans, scientists perform extensive animal studies to obtain as much information as possible about the efficacy and safety of the treatment. They then move on to phase 0 trials. This exploratory phase helps provide clinical data for the new drug and involves minimal participants.
In phase 1 trials, healthy adult volunteers are involved to verify the drug’s most frequent side effects and find out how the drug is metabolised and excreted.
Phase 2 trials establish effectiveness. This phase involves hundreds of participants to assess whether the drug works as intended and to continue monitoring possible short-term side effects.
Finally, phase 3 trials involve a much larger number of participants that include different age groups and people with comorbidities. Information on safety, dosage and effectiveness is collected.
Clinical vaccine trials in humans always begin from healthy, middle-aged adults, explains Griffin. Then healthy older adults take a turn, and eventually people with comorbidities and pre-existing medical conditions.
Pregnant women and children are considered the most vulnerable population when it comes to clinical trials and are often excluded. “We leave them to the very end, so we’ve got lots of data already supporting the use of these products,” says Griffin.
He says clinical trials that involve children are not fundamentally different, but they are even more tightly regulated. “We only do testing if it’s absolutely required and reduce any discomfort to the absolute minimum,” he says.
How do we know it’s safe to run trials in young children?
A handful of COVID vaccines have been tested in young people over the age of 12, including mRNA vaccines made by Moderna and Pfizer and the two Chinese vaccines made by Sinovac and Sinopharm. Trials have demonstrated they are safe and effective. However, a very rare side effect called myocarditis has occurred predominantly in older male teenagers and young adults following the first dose of an mRNA COVID-19 vaccine. About a dozen cases per million doses given have been recorded. Most cases are mild and resolve themselves within days.
Several countries – including the US, Israel and China – are now offering vaccines to this age group. In Australia, the Therapeutic Goods Administration has recently approved the Pfizer COVID-19 vaccine for children as young as 12, but the shortage of doses in the country means this age group is still not eligible to receive the shot.
Scientists estimate that 80% to 90% of the entire population might need to be vaccinated to achieve herd immunity. That includes children younger than 12 and extends right down to infants and babies.
Pfizer and Moderna are expanding vaccine studies to children as young as six months. Pfizer expects its vaccine to be approved for children aged two to 11 years of age as early as September. For children aged six months to two years, it might be later in the year.
Bowen says that safety signals from trials on adolescents are reassuring, but families who are keen to allow their young children to participate in the trials need to be aware of the rare heart condition recorded among older adolescents. Although this might be a severe side effect, she says, the individual risk remains very low.
“It is a really tricky dilemma,” she says. “But families need to weigh up the information that we have acquired from the trials in other age groups, and the benefits to their children, as well as what they could be contributing to the greater knowledge for other children.”
Dr Manuela Callari is a Sydney-based freelance science writer who specialises in health and medical stories.
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