LONDON—The UK Health Security Agency (UKHSA) said on Wednesday that children aged between 12 and 15 should delay getting a COVID-19 vaccine if they have recently had COVID to at least 12 weeks after they were infected. The advice brings guidance for 12 to 15-year-olds into line with that for 16 and 17-year-olds, who were advised to wait 12 weeks after infection before getting a shot when officials gave a go ahead for second doses for that age group. Currently, 12 to 15-year-olds are only advised to get an initial shot of Pfizer’s COVID-19 vaccine, which has been associated with rare, mild, and usually short-lived side effect of heart inflammation known as myocarditis. The UKHSA said that the increase in the gap, from previous guidance of a 4-week interval, could cut rare cases of myocarditis further. UKHSA said that current advice for at-risk children between 12-17 was unchanged, owing to …