A delay in deliveries from India and the need to retest a batch of 1.7m doses is behind the issues with vaccine supply in April.
The problem with a shipment from the Serum Institute of India (SII) has been blamed by the body’s chief on the country’s government, although Mr Johnson said Narendra Modi’s administration has not stopped any exports.
But Mr Johnson said despite this, targets would still be met and the road map out of lockdown was not impacted.
Speaking from Downing Street tonight Mr Johnson said: “Let me assure you that if you come forward after receiving your letter, we have the jabs for you.
“We’ve always said in a vaccination programme of this pace and scale some interruptions in supply are inevitable and it is true that in the short-term we’re receiving fewer vaccines than we had planned for a week ago.”
The delay means from March 29 volumes for first doses will be significantly constrained, with the shortfall predicted to last for four weeks.
Professor Martin Marshall, chairman of the Royal College of GPs said the focus in April will be on giving second doses to people who were vaccinated earlier in the year.
While those in their 40s are likely to have to wait until May to get their Covid-19 vaccine, when it had previously been hoped that vaccination of this group would start in April, after all of those over-50 had received their first jab.
England’s Chief Medical Officer Professor Chris Whitty said the NHS would continue to prioritise those in the most high-risk groups during the drop in vaccine supply.
Health Secretary Matt Hancock said in the Commons that the vaccine supply issues will have “no impact on the road map” out of lockdown.
He said: “We are on track for the dates in the road map and there is no impact on the road map from the changes to vaccine supply that we’ve been detailing in the last 24 hours.”
Labour leader Sir Keir Starmer said the Government needs to be clearer about the issues it faces with vaccine supply.
“The vaccine rollout has been going really, really well and that’s a good thing,” he said. “So, I am concerned about the delays, we need to get to the bottom of it and we need transparency from the Government about what the problem is. I say that in a constructive spirit because we want everybody to be vaccinated as soon as possible.”
Mr Johnson also will be marking the first anniversary of the lockdown on March 23, he confirmed, as he said the Government would be pursuing ideas for a national memorial for victims of the pandemic.
He said: “On the anniversary, of course I’ll be marking it as I’m sure billions of others will around the country. And on the idea for a national memorial, yes, we will certainly be pursuing that, and a lot of good suggestions have already come in.”