LISBON — Portugal’s vaccination campaign is almost over now, and it has exceeded even the wildest goals. Nearly an entire nation trusted in the science, officials say. At mass immunization centers, just the last trickle of teenagers is passing through. Some 85 percent of Portugal’s population is fully vaccinated — aside from tiny Gibraltar, the highest rate in the world.

“We have actually run out of adults to give shots to,” said Lurdes Costa e Silva, the chief nurse at a Lisbon vaccine center that is already half-shuttered.

Portugal’s feat has turned the country into a cutting-edge pandemic laboratory — a place where otherwise-hypothetical questions about the coronavirus endgame can begin to play out. Chief among them is how fully a nation can bring the virus under control when vaccination rates are about as high as they can go.

The emerging answer is promising — mostly. In Portugal, every indicator of pandemic severity is quickly trending downward. The death rate is half the European Union average and nine times below that of the United States.

Lisbon is triumphant: a city of live music and partying, where early-risers might find sidewalks still sticky with beer. Traffic is back to normal as people settle into the rhythms of commuting to work. And the celebrity of the moment — on glossy magazine covers — is the former submarine commander who led the country’s vaccination drive.

But Portugal’s experience is also providing a note of caution: a reminder that 1½ years into this pandemic, the current tools of science still might not be enough. The virus is still causing cancellations, lost work days and sickness — in rare cases severe. It spreads less quickly and less far than it would in places with lower vaccination rates — which benefits everyone, including the 12-and-under children not yet eligible for shots. But herd immunity remains elusive. Daily calculations about risk remain, even without large ranks of unvaccinated people to blame.

“We have achieved a good result, but it’s not the solution or miracle one would think,” Portugal’s health minister, Marta Temido, said in an interview.

The prime minister this week is set to reopen nightclubs and lift the mandatory 2 a.m. closing time for bars, on the path to what he calls “total freedom.” In reality, though, some precautions will remain. Mask-wearing indoors will still be mandatory in some indoor situations. Digital health certificates will continue to be necessary for travel and events with crowds.

Perhaps the most telling sign of Portugal’s lingering unease is this: Many health officials are still worried about a winter wave, and a rise in hospitalizations. And they are still worried about the vulnerability of the elderly to the ravages of the virus. In Portugal, seniors are vaccinated at a level verging on the statistically impossible: Official data puts the rate at 100 percent. But many were also vaccinated more than half a year ago — and studies from around the world, from the United States to Israel, have warned of a drop in protection by that point.

One of the biggest warnings of all has come from a science institute in Lisbon, where researchers have been measuring antibody levels in several thousand people — including about 500 in Portuguese nursing homes. Shortly after those nursing home residents were vaccinated, all with the vaccine from Pfizer-BioNTech, 95 percent developed antibodies, the researchers found. But this summer, when the latest batch of blood samples arrived in coolers, the scientists performed the same tests — introducing the blood to synthetic elements of the virus — and the results were even more worrying than what they had been bracing for.

The staff at the nursing home, whose blood was also tested, still had detectable antibodies. But more than one-third of the residents had lost antibodies entirely.

Jocelyne Demengeot, 58, the lead investigator at the Gulbenkian Institute of Science, described the finding as a marker of something “not optimal.”

Speaking in an interview at her institute, where scientists conduct meetings mostly outdoors, she said the results did not necessarily signal lost protection against severe illness and death. There was still a chance the seniors’ immune systems had been trained by the vaccine to better confront subsequent exposures. But waiting to find out in real life was risky. The institute alerted the government task force handling vaccination.

A wartime approach

But across Lisbon, in a windy hilltop military facility, Portugal’s much-admired vaccine czar was worried about something else entirely.

To Henrique Gouveia e Melo, most of the information arriving about the elderly was overwhelmingly reassuring. Even six months in, they weren’t filling hospital beds. Case levels among seniors were falling still.

The naval vice admiral had spent much of his career measuring risks, and he felt the biggest risk for Portugal required a bigger-picture view.

On one of the three computer screens at his desk, he pulled up a chart showing vaccination levels, country by country. The rates in many Western countries were decent to good, still rising slowly. But then he stopped on two former Portuguese colonies, Angola and Mozambique.

In both places, like in many African nations, vaccination rates remain in the single digits — potentially giving breathing room to rampant infections and new variants capable of evading vaccines and racing around the world.

Gouveia e Melo pointed at his screen.

“These countries will have their revenge on us,” he said.

While the explanations for Portugal’s vaccine success go far beyond one person — the country has fairly centrist politics and a long-standing trust in other vaccines — doctors note that the campaign was stumbling out of the gates, until Gouveia e Melo took over, demanded things be done his way, and drew up a strategy of big vaccination hubs and clear public statements.

From that point on, he became the country’s urgent, irreplicable voice: a 6-foot-4 submariner who’d spent four years of his life underwater, who had a side interest in drones, and who now obsessed over the cold metrics of vaccine deliveries, efficiency and declining mortality.

He delivered his message night after night in Portuguese TV studios, dressed in military fatigues to convey the sense of a war. In March, as news about rare blood clots linked to AstraZeneca’s vaccine threw Europe into a panic, Gouveia e Melo tried to put the risk in context. He described two roads, one for those who chose the vaccine and the other for those who chose to wait. On the road for the vaccinated, a sniper would kill one of every 500,000, Gouveia e Melo said. On the road for the unvaccinated, a sniper would kill one of every 500.

“So,” he said, “which road do you want?”

But now, Gouveia e Melo said, the situation was different. He thought Portugal’s best move would be to focus on helping others — not just for “moral” reasons, but for its own safety. He called the idea of booster shots “stupid.” To him, the domestic mission was over — and his task force, disbanded this week, was no longer needed. Portugal had earned an opportunity to help elsewhere.

“You cannot win just by vaccinating everyone in your own country,” he said. “The war ends after we give shots to everyone in the world.”

Weighing the risks

At one of the same nursing homes that had offered blood to the researchers, two scientists arrived last month, driving an hour north from Lisbon, delivering the news that had no certain interpretation. The scientists offered the nursing home director a slide show presentation, and one of the last slides showed the chart: Thirty-seven percent of the residents were now without antibodies.

“This doesn’t mean they are not protected,” the director, Joaquim Moura, remembered the scientists saying.

But Moura was left to weigh the information. Even if Portugal might soon introduce booster shots for the elderly — as the United States, Britain, France and Germany have done — what should change in the interim? How, yet again, to weigh the risks?

For the 89 residents of the Social Assistance Center of Runa, vaccination had been transformative. It relieved the extraordinary fear of a catastrophe, the sort that had unfolded in other facilities across the country and around the world.

Just as important, vaccination had allowed the center to reopen its doors. People who had been cut off from their families — falling into depression, “losing their taste for life,” Moura said — were now seeing their children. Many took shuttle trips to the nearby mall. Graça Carita, 85, who had been widowed at age 38, went on a date. Francisco Pratas, 83, who last year had taken to driving his car around the nursing home parking lot just to protect its engine, now was able to exit the gates and drive to the beach.

“By doing those kinds of things,” Pratas said, “our lives are reborn.”

Some of the residents who’d lost antibodies were too frail to receive the news themselves, so the facility’s head nurse sent emails to their families. The emails were measured, and didn’t suggest that any dramatic changes were necessary, but said there was a “bigger need to reinforce protection measures already in place” — mask-wearing, hand washing and distancing.

The nurse provided a similar message to the residents he met with in person, including Maria Apolinia, 88, and her husband, João Lopes Neves, 90. Each was then left to make their own decisions about whether or how to adjust their behavior.

Maria and João have been married for 62 years, and even during the worst locked-down days of the pandemic, they had one another. His health was worse than hers, so they slept in separate wings, but they spent the day together, from 10 a.m. until 6 p.m., sometimes sitting at a reading table, sharing the newspaper.

But until getting vaccinated, they had been cut off from their three children and seven grandchildren, whose achievements and growth were happening out of view. Even months after that contact has been restored, after many visits to their daughters’ homes for meals of beef and rabbit, Maria tears up almost immediately at the memory of last year.

So when the nursing home told them the news — Maria still had antibodies, but João did not — they talked briefly. Maria says she felt “sad.” But João brushed it off. They agreed it was too much of a sacrifice to be careful and again lose the things that mattered. Maybe the booster shots were coming, maybe not, but they kept scheduling lunches with their children, even if the risks had slightly changed.

“We’re going again this Sunday,” Maria said.

Read more: