LONDON, England (AP) — The British government’s top medical adviser has warned that the number of people hospitalised with the coronavirus could reach “quite scary” levels within weeks as cases soar as a result of the more contagious delta variant and the lifting of lockdown restrictions.

Chief Medical Officer Chris Whitty told a webinar hosted by London’s Science Museum late Thursday that the UK is “not out of the woods yet.”

“I don’t think we should underestimate the fact that we could get into trouble again surprisingly fast,” Whitty said.

New coronavirus infections in the UK are at a six-month high, according to government figures, and the number of people hospitalised and dying with COVID-19 are at their highest levels since March. Thursday’s data showed 3,786 people in hospital with COVID-19 and another 63 virus-related deaths.

At the height of the second wave earlier this year, around 40,000 people were in hospital with COVID-19 and deaths reached around 1,500 people a day.

Another 48,553 confirmed lab cases were reported Thursday, the biggest daily figure since Jan. 15. The government has warned that daily infections could hit 100,000 this summer, a level not previously reached during the pandemic, with most of the new cases being seen among younger age groups, many of whom have yet to be vaccinated.

The British government, which is lifting all remaining legal restrictions on social gatherings in England on Monday, is hoping that the rapid rollout of vaccines will keep a lid on the number of people becoming seriously ill.

More than two-thirds of British adults have received both doses of a vaccine, and almost 88% have had one dose.

More cases will inevitably lead to more people requiring hospital attention even though the vaccine rollout has helped build a wall of immunity around those deemed to be the most vulnerable to disease.

Whitty warned that the number of people in hospital with COVID-19 is doubling about every three weeks and could reach “quite scary numbers” if the trend continues.

“We are not by any means out of the woods yet on this, we are in much better shape due to the vaccine program, and drugs and a variety of other things,” he said.

“But this has got a long way to run in the UK, and it’s got even further to run globally,” he added.

The surge in infections has had a knock-on effect in the number of people self-isolating after coming into contact with a confirmed coronavirus case. More than 500,000 people were contacted by the National Health Service’s app and told to self-isolate in the seven days to July 7.

Businesses including automakers, meat processors and hospitality venues have reported staff shortages because so many employees have been told to quarantine by the app.

The government has expressed concerns about scale of the problem and are examining whether the app could be made less sensitive to reduce the numbers being pinged.