London, Mar 18 (IANS): The UK is going to face a "significant reduction" in vaccine supplies from March 29 onwards, the National Health Service (NHS) said in a letter.

The letter sent by the NHS on Wednesday to local vaccination sites across the country said volumes for first doses are going to be "significantly constrained", reports Xinhua news agency.

Disruption could last for four weeks, and the UK government's vaccines taskforce has told the health service that this is linked to "reductions in national inbound vaccines supply", according to Sky News.

In response, Health Secretary Matt Hancock said in a press briefing at Downing Street that vaccines supply is always "lumpy", adding that the NHS letter is a normal, operational note.

"I can assure there is enough supply to deliver on the offer of a jab for over-50s by the 15 April," he said.

He said under-40s won't have to wait, because the government is on track to deliver jabs to all adults by the end of July.

Vaccine supplies "sometimes go up and sometimes go down" but the government is sticking by its commitments, he said.

The latest development came hours after the UK government announced that more than 25.2 million people have been administered the first dose of a coronavirus vaccine.