Children aged 12 and who get a COVID-19 infection should not have a vaccine until three months later, officials have said.
Experts from the UK Health Security Agency (UKHSA) said that deferring the jab could help to reduce even further the "very, very small" risk of heart inflammation after vaccination.
The current case rates of myocarditis after vaccination among under-18s are suspected to be around nine per million vaccinations and cases have been "relatively mild", they said.
Officials wanted to highlight guidance which clarified when children should get a jab after a natural infection.
The current advice for older people and for people at high risk of COVID-19 – including those aged 12 and over – is that they should wait four weeks between infection and having a dose of vaccine.
But officials said this should be extended to 12 weeks in lower-risk children aged between 12 and 17.
The guidance comes amid high infection rates among younger age groups.
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And the new advice could mean that the vaccination programme is slowed slightly.
It is thought that a natural COVID-19 infection in younger people provides them with "at least" three months' protection and could extend to six months.
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On Monday, the Joint Committee on Vaccination and Immunisation (JCVI) said 16 and 17-year-olds could book their second COVID-19 vaccine 12 weeks after their first.
But the UKHSA said that should teenagers in this age group be infected with COVID-19 after their first dose, they should then delay the second dose until 12 weeks after the infection.
Those still waiting to book their first dose who have had a natural infection should also delay for 12 weeks.
The JCVI has not yet advised on second jabs for healthy 12 to 15-year-olds.
Officials estimate that around half of secondary school pupils have had COVID.
Experts reiterated that the risk of myocarditis and other side effects is "largely in the first few days", adding: "So if people had that vaccine three or four weeks ago, within a month of them having had previous infection, and are now fine, they can be reassured they're past that period of potential risk."
From Thursday, vaccination workers will start doing verbal checks to assess whether children have had a confirmed natural infection within the last 12 weeks.
People are encouraged to get their jab even if they have had previous infection to get as much protection as possible.
Dr Mary Ramsay, head of immunisations at UKHSA, said: "Based on a highly precautionary approach, we are advising a longer interval between COVID infection and vaccination for those aged under 18.
"Young people and parents should be reassured that myocarditis is extremely rare, at whatever point they take up the vaccine, and this change has been made based on the utmost precaution."
"We keep all advice under constant review and will revise it according to the latest data and evidence."