PRIME minister Boris Johnson will lead a press conference from Downing Street later today.

Mr Johnson will be joined by chief medical officer Professor Chris Whitty and MHRA (Medicines and Healthcare products Regulatory Agency) chief executive Dr June Raine, No 10 said.

The press conference will take place at 5pm.

It comes as people in their 40s are likely to have to wait until May to get their Covid-19 vaccine after problems with a shipment of the AstraZeneca jab from India impacted supply.

The head of the Serum Institute of India (SII), which manufactures the vaccine, suggested the country’s government was blocking exports to the UK.

Professor Martin Marshall, chairman of the Royal College of GPs, said news of constraints in supply was 'disappointing' and 'a bit of a setback', and the focus in April in England will be on giving second doses to people who were vaccinated earlier in the year.

“The impact of this shortage of supplies will happen on the group that we were hoping to start on in April, which is the people under the age of 50 without any pre-existing conditions, who are now going to have to wait until May,” he told BBC Radio 4’s Today programme.

Cabinet minister Robert Jenrick also conceded that the rollout of vaccines would be slower than expected because of the shortage, while Professor Adam Finn, a member of the Joint Committee on Vaccination and Immunisation (JCVI), said vaccination of those aged under 50 'may kick off slightly later than we’d optimistically hoped'.

European Medicines Agency (EMA) is to deliver its verdict on the safety of the AstraZeneca vaccine after more than a dozen European countries halted its rollout over fears regarding blood clots.

Meanwhile, the Government has announced that shielding will formally end on April 1, with those on the shielded patient list receiving letters from Thursday.

Dr Jenny Harries, the deputy chief medical officer for England, said: “With the prevalence of the virus in the community continuing to decrease, now is the right time for people to start thinking about easing up on these more rigid guidelines.

“If you have been shielding, we strongly urge you to take extra precautions following April 1 to keep yourself as safe as possible, such as continuing to observe social distancing and working from home.

“We will continue to monitor all of the evidence and adjust this advice should there be any changes in infection rates.”