A "very large number" of at-risk people could develop a "serious" coronavirus infection if the UK's lockdown restrictions are lifted now, a top medical expert has warned.
Professor Jeremy Brown said between 90% and 95% of people who are deemed high risk have been vaccinated, but mostly with one dose, which does not provide full protection.
Half of all adults in the UK have now received a jab after a bumper vaccinations week, Health Secretary Matt Hancock announced yesterday.
However the milestone will be followed by a lag in comings week as Britain faces vaccine supply delays expected to last into April.
Prof Brown, a consultant in respiratory medicine and member of the Joint Committee on Vaccination and Immunisation (JCVI), told Sky News' Sophy Ridge on Sunday it appeared likely all adults would still get their jab by the end of summer.
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But he warned people not to grow complacent and to continue to take precautions while they wait for their second jab.
Prof Brown said: "Until we have done the second dose and everyone has been vaccinated, there is a little degree of infection that still occurs.
"If you completely lift all restrictions there will be a wave of infections across the country and those who are not protected, either because the first vaccine hasn't worked very well in them and they need their second dose, or because they have not had a vaccine at this point in time but are still vulnerable, they will get infections and they will end up in hospital and die.
"So, if you lift restrictions, even though most people who are at risk have been vaccinated, the proportion who have not still represent a very large number of people who could end up with serious infection."
People who received the Pfizer vaccine for their first dose should get the same for their second, professor Jeremy Brown has said.
He told the broadcaster this morning: "I'm not an expert on supply, but everyone who got the Pfizer the first time will get the Pfizer the second time, and AstraZeneca (will be) the same.
"The supply has been matched to allow that to happen, so that should happen."
Vaccine supply issues could result in the UK's vaccination programme being "delayed slightly", Prof Brown added.
He said due to the vaccination programme being "ahead of schedule" it will likely only fall back to the original timetable.
Boris Johnson has vowed to give a jab to every adult in the UK by the end of July as he eases the UK out of lockdown.
But under-50s are warned they may have to wait longer than expected for their first doses due to expected shipment delays.
Vaccine maker Moderna confirmed this week it was on track to deliver the batches of its jab for the UK in April, boosting the programme currently relying on stocks of Oxford/AstraZenca and Pfizer/BioNTech.
Prof Brown continued: "It does look like we have been making a vaccine programme that is doing almost five million a week, which would be a fantastic result if we could maintain that.
"But it has always been the supply of vaccine that has been the concern that might delay things, and, yes, I suspect our vaccine programme will be delayed slightly compared to where we thought it might have been a few weeks ago.
"But then we are then ahead of schedule, so we are probably going to fall back to the original schedule and end up with everyone who is an adult being offered a vaccine by towards the middle to end of the summer."
