The Cabinet Office has indicated that an average of 2.7 million doses a week will be given in England until the end of July, down from a previous estimate of 3.2 million.
The Prime Minister’s official spokesman refused to be drawn on “details around supplies and deliveries” of vaccine doses but said “we remain on track” to meet the targets set for the programme.
Supplies of vaccines in April have been constrained by the need to test a batch of 1.7 million doses and delays in a shipment of around five million from India..
The Prime Minister’s official spokesman said: "The Health Secretary set out a couple of weeks ago now the fact that there will be a slight reduction in April but the key thing to remember is that doesn’t mean that we are not on track to hit our pledges.
"We remain on track to vaccinate all those in phase one by April 15, we remain on track to vaccinate or provide the first dose to all adults by the end of July."
The rollout will be boosted by the introduction of Moderna jabs later in April alongside the Pfizer and AstraZeneca vaccines already being used.
"I’m not going to get into the specifics of how many we will get this month," the spokesman said, but "we will have three vaccines that we are able to distribute and that will ensure that we can continue to make sure we are giving people their first doses as well as giving more and more people their second doses".
Across Cambridgeshire and Peterborough, nearly 12,000 second doses had been administered to people under the age of 50, many of whom will be frontline healthcare workers who were offered the first vaccine in the early stages of the rollout.
A further 7,355 doses were given within the Peterborough local authority within the week leading up to March 28. A total of 81,296 doses - including any second doses given - have been given to people over the age of 16 since the beginning of the programme.