Mary Ramsay, head of immunisations at Public Health England, said this would only happen on extremely rare occasions, and that the government was not recommending the mixing of vaccines, which require at least two doses given several weeks apart.

“When there are at least five such reports, we will put information on our website about the type of reactions that have occurred,” the agency’s Chief Physician Maija Kaukonen told the broadcaster, adding that no further details could be disclosed due to patient confidentiality.