US biotech company Moderna said this week that it plans to test its new-technology COVID vaccine on children aged 12 to 17. The intention was listed at clinicaltrials.gov but recruiting hasn’t started yet.

The trial will include 3000 children, half of them receiving two injections four weeks apart, and half injected with salt water as a placebo.

With some adults potentially becoming vaccine hesitant at the prospect of a brand new treatment for an equally new disease, the issue of children being vaccinated against the coronavirus is to a certain extent bound to be a contentious one.

Should kids be first or last in line?

Some experts have argued that children should be vaccinated first, to protect the elderly.

Others say that kids won’t be vaccinated until late 2021 because researchers will need to determine the dosages, interval between doses, and the number of doses that work best in children – a process that could take several months.

But things are moving fast. Within days, Pfizer will roll-out 800,000 doses of its vaccine in Britain, under emergency authorisation. Another 40 million will follow.

Some kids have already taken part in a trial

In all the excitement, one little discussed fact is that Pfizer already trialled its vaccine on children – the company’s Phase II-III trial included people aged 12 and over. Apparently the younger participants tolerated the vaccine equally as well as the adults.

“The word coming out from the Pfizer camp is that it’s equally efficacious in all age groups, and you don’t see a particular change in the safety profiles, which is good,” said Professor Catherine Bennett, Chair in Epidemiology, Deakin University.

“At the same time, even in these countries where they’re rolling out under emergency direction, the priorities are always going to be the elderly and the front-line workers, in the first instance – and then work down through age groups. So the younger ones will be toward the end anyway.”

The rationale is that younger people are at less risk of becoming ill with the virus – and while this places them in the worrying class of asymptomatic cases, children tend not to be a notable source of transmission.

Every vaccine will require special testing on children

Pfizer began testing its vaccine on children in October. Vaccines are ordinarily tested on adults first.

Moderna’s vaccine was tested on 30,000 adults and was found to have high efficacy (94.5 per cent effective in preventing disease) and a solid safety profile.

The company plans is seeking ’emergency use authorisation’ from the US Food and Drug Administration with a view to rolling out 20 million doses to elderly Americans and health workers this month.

While the trial on children has been listed at clinicaltrials.gov, there’s no indication yet when recruiting might start or where the testing sites will be.

Why kids need special consideration

Dr. William Schaffner, an infectious disease specialist at Vanderbilt University and an adviser on vaccines to the Centers for Disease Control and Prevention, told The New York Times that children have more active immune systems than adults, and may have stronger reactions, including more fever, muscle and joint aches and fatigue.

“They may be more out of sorts than adults for a day or two,” he said. “You really do want to know, if it’s given in adolescents, what can parents expect? You really want to be able to tell them clearly how you might feel for 24 or 48 hours after you receive the vaccine. And obviously, we really want to be able to tell parents it works.”

This is important, especially with a vaccine that requires more than one injection. If parents are confronted with side effects they haven’t been warned about, they they might be reluctant to go back for the second shot, Dr. Schaffner said.

It’s also worth keeping in mind that the Pfizer and Moderna vaccines have star billing for now. But there are other vaccines on the way, and some are expected to potentially outperform Pfizer and Moderna. So by the time we’re ready to vaccinate children on a global scale, thousands of kids will have gone through the various trials to show these vaccines work and are safe in  smaller bodies.