LONDON — When Prime Minister Boris Johnson fumbled his initial response to the coronavirus pandemic, his political fortunes faltered, only to rebound quickly thanks to Britain’s surprisingly effective vaccine rollout.
With his popularity now waning again — this time following a broken promise not to raise taxes — Mr. Johnson is hoping that history will repeat itself.
On Tuesday, he announced a campaign to offer vaccine booster shots to people aged 50 and over, as well as first shots to three million children, aged 12 to 15 — all while reiterating his vow to avoid future lockdowns.
Should winter bring a surge of new cases, however, he could reintroduce mandatory mask-wearing, roll out vaccine passports, and urge workers to stay home if possible, under what the government calls its “Plan B.”
“We’re now in a situation where so many of the population have some degree of immunity, smaller changes in the way we’re asking people to behave can have a bigger impact,” Mr. Johnson said at a news conference.
For now, the prime minister is placing his faith in a redoubled vaccine campaign to protect Britain’s health service from being overwhelmed, and to save him from having to order fresh lockdowns that would depress the economy and infuriate a noisy caucus of his own lawmakers.
“The vaccine bounce helped him the first time around and if the booster plan — which will be a massive story in British politics — goes well and he’s able to say the rollout is going to plan, that will potentially help him,” said Matthew Goodwin, professor of politics at Kent University.
But Mr. Goodwin added, “he is certainly vulnerable in terms of his internal critics.”
For a leader who often seems to defy political gravity, the risks are high because, for the first time in months, poll ratings are slipping for Mr. Johnson’s Conservative Party. Last week, he announced plans to raise taxes and there are growing doubts about his pledge to “level up” economically disadvantaged areas.
There are also signs that some of the new voters Mr. Johnson attracted in the 2019 election might be drifting away. “His premiership currently doesn’t seem to have delivered on the things that these voters want,” Professor Goodwin said.
It was a looming funding crisis in health and social care programs that forced Mr. Johnson to break his word and agree to raise taxes on workers, employers and some investors. Not only has that put at risk his party’s reputation for low taxation, but it has also angered several prominent party donors.
Support for the Conservatives dropped by five points to 33 percent, according to a recent opinion poll conducted by YouGov, with the Labour Party up one point to 35 percent, putting it in the lead for the first time since January.
Part of Mr. Johnson’s difficulty is that, while surveys generally show that the British public favors strict measures to contain the virus, lockdown restrictions are anathema to a noisy libertarian wing of his own Conservative Party.
So while the government did not rule out the possibility of further tough restrictions, it made clear they would be a very last resort after exhausting “lockdown lite” measures, such as mandatory mask wearing or vaccine passports.
On Tuesday, Mr. Johnson emphasized the success of the vaccination campaign, which he said had produced “one of the most free societies and one of the most open economies in Europe.” He added, “That’s why we are now sticking with our strategy.”
Public-health experts generally supported Mr. Johnson’s announcements, though some noted that Britain, as usual, seemed to lag other countries on issues like vaccinating young people or encouraging the use of face masks.
“They always get there, just later than they should,” said Devi Sridhar, head of the global public health program at the University of Edinburgh.
Britain, she said, was “heading in the same direction as other countries, but with a major delay” in vaccinating those aged 12 to 15, drawing up contingency plans for mandatory mask wearing and vaccine passports, and boosting testing to get the country through what is likely to be a difficult winter.
Monday’s decision to vaccinate children as young as 12 was contentious, though many other countries, including the United States, France, Italy and the Netherlands began doing so months ago. The British government’s advisory group, the Joint Committee on Vaccination and Immunization, had previously concluded that the health benefits for those aged 12 to 15 were marginal. That prompted a debate over the ethics of vaccinating children to prevent the spread of a virus that is a health risk to the adults with whom they live and meet.
On Monday, the chief medical officers of England, Scotland, Wales and Northern Ireland, argued that, by reducing the disruption in schools, a vaccination campaign would bring other benefits to young people.
Similarly, the decision on boosters puts Britain among a growing group of countries that are offering additional shots to their own citizens before many people in large parts of the world have received even one dose, provoking criticism from David Nabarro, a special envoy on Covid for the World Health Organization.
Understand Vaccine and Mask Mandates in the U.S.
- Vaccine rules. On Aug. 23, the Food and Drug Administration granted full approval to Pfizer-BioNTech’s coronavirus vaccine for people 16 and up, paving the way for an increase in mandates in both the public and private sectors. Private companies have been increasingly mandating vaccines for employees. Such mandates are legally allowed and have been upheld in court challenges.
- Mask rules. The Centers for Disease Control and Prevention in July recommended that all Americans, regardless of vaccination status, wear masks in indoor public places within areas experiencing outbreaks, a reversal of the guidance it offered in May. See where the C.D.C. guidance would apply, and where states have instituted their own mask policies. The battle over masks has become contentious in some states, with some local leaders defying state bans.
- College and universities. More than 400 colleges and universities are requiring students to be vaccinated against Covid-19. Almost all are in states that voted for President Biden.
- Schools. Both California and New York City have introduced vaccine mandates for education staff. A survey released in August found that many American parents of school-age children are opposed to mandated vaccines for students, but were more supportive of mask mandates for students, teachers and staff members who do not have their shots.
- Hospitals and medical centers. Many hospitals and major health systems are requiring employees to get a Covid-19 vaccine, citing rising caseloads fueled by the Delta variant and stubbornly low vaccination rates in their communities, even within their work force.
- New York City. Proof of vaccination is required of workers and customers for indoor dining, gyms, performances and other indoor situations, although enforcement does not begin until Sept. 13. Teachers and other education workers in the city’s vast school system will need to have at least one vaccine dose by Sept. 27, without the option of weekly testing. City hospital workers must also get a vaccine or be subjected to weekly testing. Similar rules are in place for New York State employees.
- At the federal level. The Pentagon announced that it would seek to make coronavirus vaccinations mandatory for the country’s 1.3 million active-duty troops “no later” than the middle of September. President Biden announced that all civilian federal employees would have to be vaccinated against the coronavirus or submit to regular testing, social distancing, mask requirements and restrictions on most travel.
“I’m a bit upset, frankly, to hear that Britain is going into boosters, when this is simply going to take really precious vaccine away from people in other parts of the world who can’t get their basic two doses, and therefore going to be at risk of death,” he told Times Radio.
The question for Mr. Johnson is whether vaccines and his light-touch approach to other restrictions will be enough to forestall more draconian measures.
Graham Medley, an epidemiologist who is advising the government, said that in England, the reproduction rate for the virus was hovering around one, meaning that the epidemic was still circulating widely but not spreading exponentially. He said he did not expect a return of the high levels of infection of last January.
Still, Professor Medley said the divergent experiences of other parts of the United Kingdom, notably Scotland, where infection rates have fluctuated dramatically, showed how unpredictable the virus remained. None of the models predicted that cases in England would fall, rather than rise, in July, he said.
“We are still waiting for the full effect of schools reopening and people going back to work,” said Dr. Medley, a professor of infectious disease modeling at the London School of Hygiene & Tropical Medicine.
Britain is still reporting more than 25,000 cases of the virus a day, and hospital admissions are running at roughly 1,000 a day. That is enough to strain the National Health Service, which also has to tackle a huge backlog of procedures that had to be postponed during the pandemic.
Mr. Johnson’s gamble in lifting most restrictions in July appeared to pay off when new cases fell rather than rose. But with schools opening across England over the last two weeks, that surge in infections could still come. Cases soared in Scotland, where schools opened earlier.
Mr. Johnson’s gamble is that a new vaccine roll out, with minimal restrictions, will be enough to avert a big rise in hospitalizations.
Avoiding further lockdowns is critical for Mr. Johnson, Professor Goodwin said, adding that the some of his own lawmakers would be up in arms even if measures like mask wearing were reintroduced to combat the spread of the virus.
“They really want to see us move on and learn to live with it,” he said.