NEW YORK (BLOOMBERG) - William Brown has yet to set foot in a classroom during his freshman year of high school - kept at home, like many students, by the pandemic.
Days before Christmas, he took a step that could help him and other youngsters return to school sooner. With his parents' encouragement, the 15-year-old signed up for a trial of Pfizer's vaccine in adolescents.
"I miss seeing all my friends, and being in person, talking to my teachers," William said by phone from Raleigh, North Carolina. "Hopefully, me doing this will allow people my age to get back to school."
In the United States, more than 14 million Covid-19 shots have been given since mid-December, mainly to health workers, the elderly and those at high risk. To defeat the pandemic and fully revive the economy, children will also have to be immunised, experts said.
Burden on parents
To that end, trials to make sure vaccines are safe for the young are beginning in earnest. Pfizer and Moderna started recruiting participants at the end of last year, and could have data from studies by summer. The University of Oxford, which developed a vaccine with AstraZeneca, is planning initial tests in 12- to 18-year-olds next month.
"If you want to get this under control, you need to vaccinate kids," said Dr Paul Stoffels, chief scientific officer at Johnson & Johnson. He estimates J&J will start trials for children four to six weeks after receiving results from its adult studies, which are expected by early February.
Governments around the world have repeatedly shut schools and nurseries to help curb the virus, burdening working parents and the economy. While the young do not generally suffer from severe Covid-19, immunising them could reduce the spread to people at higher risk.
"The main rationale for vaccinating children, given that they're relatively unaffected, would be to try and have an impact on transmission of the virus," said Professor Andrew Pollard, lead investigator on the Oxford trials, in an interview.
The adolescent trial of the Pfizer vaccine, created with German partner BioNTech, has completed enrolment, with 2,000 volunteers aged 12 to 15 participating, according to Dr John Vanchiere, principal investigator for the trial site at Louisiana State University Health Shreveport. A Pfizer spokesman declined to confirm that enrolment was finished, and said the company will share data in time.
Moderna gave its first doses to young volunteers last December, and plans to have initial data from its 3,000-strong trial of 12- to 18-year-olds in time for possible approval before the 2021 school year. But the company has been struggling with enrollment, said Dr Moncef Slaoui, chief scientific adviser to the US's Operation Warp Speed programme, which aims to accelerate the development and distribution of vaccines.
"It's been a real challenge," Dr Slaoui said at a briefing on Wednesday. After four weeks, Moderna and its partners at the National Institutes of Health had "only recruited about 800 subjects in the trial", he said.
A spokesman for Moderna, based in Cambridge, Massachusetts, said enrolment was lower over the holiday season but that the company expects a pick-up and is on track to provide updated data by around mid-year.
At Oxford, the university plans to recruit about 120 children in both the 12-to-18 and 6-to-11 age groups, Prof Pollard said. AstraZeneca will then run a larger trial for children in the US. The company declined to provide information on the size or timing of that study.
How quickly governments roll out vaccines for kids may depend on how much data scientists can gather on the role children play in transmission, and how much vaccines can stop the spread. Little is known so far about either.
Most clinical trials for children start with teenagers and work their way down for safety reasons. A number of investigators said children under five may be included in future trials, but routine inoculations for young kids and babies can make those studies harder to organise. They are also more difficult for parents, who must monitor symptoms closely.
"We have a long history of ensuring clinical trials among children are quite safe," said Prof Lee Beers, president of the American Academy of Pediatrics. "That's why you enrol in phases. At the point that you get to paediatric trials, you've already gone through adult trials where they've demonstrated safety."
Children over 12 will receive the same dose as adults in the Pfizer, Moderna and Oxford trials. In a pandemic, it is better to avoid multiple dose formulations unless there is a difference in tolerability, Oxford's Prof Pollard said. That may change, however, as pharmaceutical companies work their way towards younger children.
The main driver for Covid-19 child vaccinations is achieving herd immunity, according to Professor Beate Kampmann, director of the London School of Hygiene & Tropical Medicine's vaccine centre. That is unlikely to be achieved if more than a quarter of the global population is unprotected.
"Children are part of the transmission chain, so eventually, if we want to get to the stage of herd immunity, they have to be included in vaccination schedules," said Prof Kampmann.
Back to normal?
Given that other coronaviruses do not induce lifelong protection, either naturally or through vaccines, it is unlikely that Covid-19 shots will do so, Prof Pollard cautioned. But they could prevent severe disease, and vaccinating children might be important for that effort.
For students, as well as parents overwhelmed by the pandemic, a vaccine for children could mean a return to normalcy.
"This year has been the strangest anyone has ever experienced," said Ms Lisa Brown, William's mother. "It's important for this age group to get vaccinated so that they can go back to school, and things can go back to normal."