LONDON, Jan 7 (Reuters) - The head of England's National Health Service reassured people that they would get their second COVID vaccinations after some appointments were cancelled in order to prioritise giving out more initial doses of the shot.

"People will get their second jabs (shots), whether that's Pfizer or AstraZeneca," said Simon Stevens, Chief Executive of the National Health Service (NHS), when asked by Reuters at a news conference about the change in guidance which delays second shots for most people to up to 12 weeks after the first dose.

He added that the reprioritisation of shots would mean that twice as many people would be offered first doses of the vaccine over the next several weeks. (Reporting by William James and William Schomberg, writing by Alistair Smout; editing by Michael Holden)