Young people who have had only one dose of the COVID-19 vaccine could still end up in hospital from the virus, an expert has warned.
Professor Andrew Hayward, from University College London and a member of the government's Nervtag advisory group, said that while it is positive that two doses of vaccine are protecting people against the Indian variant of coronavirus, people who have only had one dose remain vulnerable, including the young.
He said: "It is very positive that two doses of vaccine are highly protective against the Indian variant, so for people who have had those two doses of vaccine and are a couple of weeks beyond that then I don't think they need to be overly worried.
"On the other hand if you've only had one dose of vaccine then the protective effect appears to be about 30% – it's probably a bit better than that – against hospitalisation, but you can still end up in hospital as you're hearing, even if you're young."
He said while the outcome might not be so bad as previously, it would still be a "very unpleasant experience" and could involve having to be administered oxygen, as well as the risk of having long COVID.
Watch: Boris Johnson admits road map could be delayed because of Indian variant
He added: "On top of that, we are seeing a doubling of cases (of the Indian variant) every week, and at a very minimum estimate it’s about 7,000 cases last week, it only takes five or six doublings for that to get up to say a quarter-million cases, and then you could set the pressure on the NHS and avoidable illnesses."
He said when further restrictions were lifted "instead of doubling every week it’s likely to double more frequently than that of course, so I think there is a good argument for caution until such time as we’ve got a much higher proportion of the population double vaccinated."
Prof Hayward's comments come amid speculation over whether restrictions will still be lifted next month as the Indian variant of coronavirus continues to spread.
Some experts argued on Friday that restrictions should remain in place until more of the population have received both vaccine doses, with Professor Christina Pagel, from University College London and a member of Independent Sage, saying reopening should be delayed for a few more months.
The latest seven-day average for daily hospital admissions in England is 88 (up to 25 May) - an increase of 15% on seven days earlier.
The figure means hospital admissions are back to where they were at the start of May and remain 98% below the second-wave peak in January.
Public Health England (PHE) data shows that the majority of people with the Indian variant have not been vaccinated, with just 3% of cases (177 out of 5,599) from 1 February to 25 May having received both doses.
Of 201 people who ended up in A&E, just five people had had both vaccine doses, while 138 were unvaccinated and 45 had had their first dose more than three weeks previously.
Of 43 patients who needed to be admitted to hospital overnight, only one person had had both vaccines, the PHE data showed.
Over the period there were 12 deaths linked to the variant, of which eight were among the unvaccinated.
Dr Helen Wall, senior responsible officer for the COVID vaccine programme in Bolton - one of the hotspots for the variant - said there are "significant numbers of 30- and 40-year-olds" going into hospital there, and tens of thousands of people in the area who have only just become eligible for the vaccine.
But she told BBC Radio 4’s Today programme that hospitals were seeing patients who were far less sick than previous COVID patients.
Dr Mike Tildesley, from the University of Warwick and a member of the Scientific Pandemic Influenza Group on Modelling (Spi-M) group, told BBC Breakfast that cases will go up but vaccines are proving to help.
Amid growing concerns, Boris Johnson told reporters on Thursday he "didn’t see anything currently in the data:" to divert from the June reopening target, adding: “But we may need to wait.”
Watch: What is long COVID?