Covid-19 vaccines are being trialled in children, with early results from Pfizer showing remarkable efficacy and tolerability. But whether any are approved for use this year may depend on how the virus behaves, say experts.

Last week, The Daily Telegraph reported that children in the UK will start getting vaccinated for covid-19 as early as August. When contacted by New Scientist, a spokesperson for the UK Department of Health and Social Care said that no decisions have been made on whether children should be offered vaccinations. “While clinical trials are under way to test the efficacy and safety of covid-19 vaccines in children and young adults, these trials have not concluded yet,” they said. “We will be guided by the advice of our experts on these issues, including the Independent Joint Committee on Vaccines and Immunisation (JCVI).”

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“I think it is very unlikely that the JCVI will have enough information from the clinical trials of current vaccines to recommend immunising teenagers or children in the summer this year,” says Saul Faust, professor of paediatric immunology and infectious diseases at the University of Southampton, UK. “The only situation that could change this would be the rapid spread of a new, more dangerous mutation. But with the current timetable for ending lockdown and the success of the adult immunisation programme, this is not something I expect to happen.”

Trials of covid-19 vaccines in children are needed in order to work out the appropriate dose, as well as to ensure they are safe and have no unexpected side effects. Older children tend to be vaccinated in trials first, followed by younger children. “The dose we give adults is likely to be OK in teenagers, but if too many minor side effects, like fever or arm pain, occur then we can lower the dose as we go down to younger – and therefore smaller – children,” says Faust.

On 31 March, Pfizer announced the first results for any covid-19 vaccine in children. In a phase III study of children aged 12 to 15 years old with and without prior covid-19 infection, the vaccine had a 100 per cent efficacy and was described by Pfizer as being well tolerated. The trial included 2260 children in the US, half of whom received two doses of the vaccine, while the rest were given a placebo. Eighteen cases of covid-19 occurred in the placebo group, compared with none in the vaccinated group. Side effects were similar to those seen in 16 to 25 year olds.

Pfizer says that it plans to submit the data to the US Food and Drug Administration (FDA) and request the use of the vaccine in children over the age of 12 as quickly as possible. Last week, the company also began a trial of the vaccine in children aged 6 months to 11 years old.

In the UK, the team behind the Oxford/AstraZeneca vaccine has started a phase II trial in children aged 6 to 17 years old. It involves 300 children, and up to 240 of these will receive the covid-19 vaccine. The rest will get a meningitis vaccine, which has been shown to be safe in children but may cause similar reactions, such as a sore arm.

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After these initial safety trials, there is likely to be a bigger study of around 4000 to 6000 children, says Faust, which would look at dosing and efficacy. It is only at this point that you would expect to see the JCVI endorse the roll out of the vaccine in children in the UK. Even when we do have data from larger trials, the JCVI will probably base its decision to roll out the vaccine on how much community transmission there is and how much children are contributing to it, says Faust.

Currently, children aren’t thought to be at risk of severe covid-19. However, they can transmit the virus and add to the overall risk of a dangerous mutation occurring as it passes between individuals. In addition, there has been a slight increase in infections among children aged 11-15 in England, according to latest data from the Office for National Statistics.

Therefore, it is likely that teenagers will be immunised first, followed by younger children, says Faust.

“If we are to reach herd immunity through vaccination, we will definitely need to vaccinate everybody who might be infectious, and that will include children,” said Peter English, former chair of the BMA Public Health Medicine Committee, in a statement. “In terms of priorities, older children will be a higher priority, because they are more likely to infect others.”

There are several other trials of covid-19 vaccines in children under way. CanSino Biologics, based in Shanghai, China, is developing a vaccine similar to the Oxford/AstraZeneca one. Researchers there are analysing initial data from a phase II trial carried out in Taizhou, Jiangsu province, in 30 children aged between 6 and 12 years old, who were each given two shots.

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Johnson & Johnson has also announced plans to study its vaccine in children, starting with those aged 12 to 17 years old, with results expected “later this year”, said CEO Alex Gorsky at a Washington Post Live event on 4 March. He said the firm was working with the FDA to ensure the right information was collected for rapid approval, and that he was hopeful children in the US would have a vaccine available by the end of the year. Moderna has said it plans to test its covid-19 vaccine in children aged 12 to 17 years old.

A representative from New York-based Codagenix told New Scientist they think their vaccine will be particularly well-suited for children given that it is administered via intranasal drops rather than an injection. However, it is currently only in a phase I trial in adults.

Several companies are also planning studies of the vaccine in pregnant women in their second and third trimesters. “All we can say at the moment is that they are coming,” says Chrissie Jones at the University of Southampton, UK, who specialises in vaccines during pregnancy. She says that Johnson & Johnson is likely to start its study in the US in May, with Pfizer shortly after this in the UK.