LONDON — Prime Minister Boris Johnson is calling it the "exit wave," a final, inevitable rise in coronavirus infections, hospitalizations and deaths that the British government says will follow when it opens up England next week on "Freedom Day."

The prime minister says all legally enforceable measures to control the coronavirus will end in England on Monday — when wearing masks and maintaining social distance will become a “personal decision,” even in London subways, pubs and packed nightclubs filled with unvaccinated young adults.

It’s a big gamble for Johnson’s premiership — and this is a government that has struggled to get it right during the pandemic. Britain today has the highest infection rates in Europe, after Cyprus, and a total of over 128,000 deaths.

At his news conference confirming the end of all lockdown measures next week, the prime minister and his scientific advisers used a new term — “exit wave” — to suggest that this will could be a last spasm of infection, in the country’s go-for-broke bid to end all legal diktats to control the pandemic and get back to normal.

The government’s top scientific adviser, Patrick Vallance, called it “our last big wave,” and “exit wave” certainly sounds better than third, fourth or fifth wave.

The idea seems to be: It is better to get it over with now, to weather the forecast rise in infections in the summer, instead of in the winter, when seasonal flu returns and there will be more pressure on hospitals.

“If not now, then when?” Johnson said.

Letting the virus go, and reaching a plateau of herd immunity sooner rather than later, is an approach that Britain considered at the very beginning of the pandemic in March 2020 — before the development of successful vaccines — and then abandoned.

The British press has dubbed Johnson’s gambit “the big bang” of reopenings.

What happens in an exit wave? Unknown.

Health Secretary Sajid Javid told England to brace for 100,000 new infections a day, triple the number today, but with far fewer cases of serious illness than in previous waves, because the vaccines are “doing their job” and protecting the aged and vulnerable.

Javid, a former treasurer, said that the economy needs to fully reopen and that endless restrictions are hurting schoolchildren and the country’s mental health.

But even with one of the best vaccine campaigns in the world, fully one third of the 67 million people living in Britain remain susceptible to the virus because they have not been fully vaccinated or previously infected.

This is a huge pool for the virus to swim in, especially the highly transmissible delta variant, first detected in India, which now dominates here.

British scientists say they aren’t really sure what happens in an exit wave because they have no idea how the public will behave Monday.

Cases will certainly rise, but the disease modelers informing the government do not know if the numbers will explode or slowly climb. They are closely monitoring the day-to-day mobility of the population through Google data, footfall cameras in transport hubs and surveys of self-reported daily contacts.

The greatest variable, say the modelers, is what the public does. Does everyone “go mad and party” starting Monday? asks Matt Keeling, professor of populations and disease at the University of Warwick. Or do people very slowly, very gradually emerge from lockdown measures and choose to sometimes wear masks and limit the number of daily contacts? This would give the government more time to give more vaccine doses.

“The public will decide what wave we have, a big peak or a flat one,” Keeling said.

England’s chief medical officer, Chris Whitty, said, “This exit wave will happen no matter what.”

He said what kind of wave it is all depends on public behavior.

Annie Cori, a lecturer in ­infectious-disease modeling at Imperial College London, said this is uncharted territory.

“So far we have not lived in a country without restrictions for the last 18 months,” she said. “And we have a more transmissible virus.”

The modelers can imagine “scenarios that lead to very high numbers,” Cori said.

An anxious British public appears divided over whether to continue with legally enforceable measures.

An Opinium poll for the Observer newspaper found that half of those surveyed said “Freedom Day” on July 19 should be pushed back, while 3 in 4 respondents believe wearing masks on public transport should continue.

Mike Ryan, head of emergencies for the World Health Organization, has urged countries such as Britain to slowly lift measures “so as not to lose the gains that they’ve made.”

Scotland, for example, plans to lift more restrictions Monday but keep “sensible precautions” by mandating masks.

Dealing with an exit wave is not Britain’s challenge alone.

After seeing infections spike again in the Netherlands after most restrictions were lifted, Dutch Prime Minister Mark Rutte last week apologized for “an error of judgment” in scrapping the measures.

Dutch cases are up 400 percent in the past two weeks. Cases in Spain and Greece are up more than 200 percent. The numbers in Denmark and Britain have increased more than 100 percent, while cases in Portugal and Belgium have roughly doubled. All these countries have relatively advanced vaccine programs.

Deepti Gurdasani of Queen Mary University of London and colleagues, writing in the British medical journal the Lancet, called Johnson’s move to completely open “dangerous and premature,” and they highlighted the worries over more people suffering from long-haul covid.

But Neil Ferguson, a top epidemiologist whose models inform government planning, told BBC Radio that the Johnson plan is “a slight gamble. It’s a slight experiment at the moment, and I think it’s justifiable, and I’m reasonably optimistic, but policy will have to remain flexible.”

Ferguson said that unlike in earlier waves, with the protection offered by vaccines and the fact that more of the infected may be younger, 50,000 cases a day would translate to 50 deaths and not 500, which would have been the forecast last year.

British officials have never said what an acceptable number of deaths might be. Instead, they have made protecting the National Health Service from being overwhelmed a top goal.

Graham Medley, professor of infectious-disease modeling at the London School of Hygiene & Tropical Medicine, said he had never heard the term “exit wave” until the prime minister used it Monday. Then again, he confessed “lockdown” was a new descriptor, too.

He said calling it an exit wave does put “a positive spin” on what might just be another wave of infection. Medley said the epidemic in Britain will slow when enough people become immune — either through infection or vaccination. Calling it an exit wave, he cautioned, “doesn’t preclude further waves in the future.”