Pfizer, AstraZeneca COVID vaccines are not yet approved for kids. How are clinical trials run for children?
Neither of Australia’s COVID-19 vaccines have been approved for children, with the Pfizer option recommended for those aged 16 years and older and the AstraZeneca shot only for adults.
- Kids don’t tend to get as sick with COVID-19 as adults
- Children are included in phase three of Australia’s vaccine rollout
- It’s important for them to get vaccinated to achieve herd immunity
So why weren’t children prioritised in the first phase of the coronavirus vaccine rollout? And how are children involved in vaccine clinical trials?
Asha Bowen, a paediatric infectious diseases specialist at Telethon Kids Institute and Perth Children’s Hospital, said it was a bit unusual that an approved vaccine had specifically not been tested in children.
“Most of our models of vaccinations are preventing vaccine-preventable diseases as early as possible,” she said.
But with COVID-19, it’s a different story.
Kids and COVID-19
Dr Bowen said it wasn’t yet clear why kids are not a major source of COVID transmission.
“I think that’s what our scientists are trying really hard to figure out,” she said.
“It’s unusual from a respiratory virus perspective, where we usually see kids getting really sick, and also really dominantly involved in transmitting the virus.”
Dr Bowen said children played a role in transmitting influenza, for example, which is why the yearly flu jab rollout includes kids.
Nicholas Wood, a paediatrician and researcher at the University of Sydney, explained that because children don’t seem to catch as many infections or present with as much severe disease, there had been no “urgency” to develop a childhood COVID-19 vaccine.
How are children involved in clinical trials?
Before the Therapeutic Good Administration grants approval for a vaccine, it must be tested extensively — first in labs, then in animals and, finally, humans.
The first phase of clinical trials usually involves healthy adult volunteers, with latter phases involving a broader range of participants, including children.
Robert Booy, senior professorial fellow at the National Centre for Immunisation Research, said trials started with older children, then gradually include younger groups.
“Once there is evidence of good, safe protection in older age groups, be they young adults or older teenagers, then you move down incrementally at five or 10 years at a go,” he said.
Dr Bowen said trials involving different age groups were sometimes run concurrently if there was enough safety data available about the drug.
And while children were “very, very rarely” included in medication trials, Dr Bowen explained, it was usually the opposite case with vaccines.
But given COVID-19’s epidemiology, she was satisfied that Australia’s vaccine manufacturers had followed the “appropriate pipeline”.
“And to then run the same clinical trials in children, to work out whether the vaccine is safe and also whether it has benefits is really important.
“At this point in time, it is an absolute gift that children are not getting sick with COVID, and so we have this opportunity to wait.”
Dr Wood agreed.
“If it had been the other way around, and children were dying and thousands were being infected, [researchers] probably would have jumped quite quickly from an adult trial to a younger children trial,” he said.
Ethical considerations for children’s trials
Dr Wood said before taking part in a clinical trial, it was important to clearly communicate potential risks to those taking part and their guardians.
Because children under 18 years are yet to meet Australia’s legal age of consent, researchers ask teenagers and kids in older age groups to agree to participate.
Older age groups get tailored information explaining what will happen, but for very young participants, the onus is on the parents.
“We can’t do that [provide information] for one- or two-year-olds. That’s very much dependent on the parents,” Dr Wood said.
Dr Bowen said before enrolling children, researchers needed to understand safety parameters.
These include having a clear understanding of side-effects, because in the unlikely event something went wrong, the consequences could last the child’s lifetime.
She said adults could give consent and understand the risk potential and possible benefits.
And generally, she added, it’s easier for researchers to predict how a drug might work in adults.
That’s because adults, being fully mature, have a relatively stable body physiology compared to children, who are still growing.
So when will kids get vaccinated?
If Pfizer and AstraZeneca’s testing goes well, Australia has included children in the vaccine rollout’s third and final phase, earmarked to begin between September and November this year.
Dr Bowen is optimistic the vaccines will be approved for use in children by the Therapeutic Goods Administration before then.
“We have seen this vaccine develop very, very rapidly, and the safely profile of it has been very, very good,” she said.
“I’m hoping that by the time we do get to phase three, there will be safety data and efficacy data for children to also be vaccinated.”
Dr Wood said even though they weren’t getting as sick as older people, involving children was important to develop herd immunity, as they likely played some role in transmitting the virus.
“If a vaccine works to stop transmission, then we basically want to give it to everyone to get the herd immunity effect so we can stop transmission of the virus,” he said.