Rapid Covid-19 vaccination rollouts in Israel, the U.K. and Chile hold an important lesson for the U.S. as it navigates back to normalcy: Risks remain, even after inoculating a significant share of your population.
The three countries have so far had contrasting experiences. Israel has reopened its economy and is closing down its Covid-19 treatment wards. Chile, by contrast, has locked down again and shut its borders. The U.K. is taking it slow, with a staged reopening planned over the next few months.
Epidemiologists say the risk is real of a so-called exit wave of new infections as countries drop their guard while shots increase, since vaccines don’t provide 100% protection against contracting Covid-19. New coronavirus variants that can evade the immunity conferred by vaccination or past infection heighten the risk of another surge.
Ease restrictions too rapidly and the virus will seize its chance, scientists say.
“We’re in a kind of foot race between vaccination and virus,” said Graham Medley, professor of infectious disease modeling at the London School of Hygiene and Tropical Medicine.
Still, even with a new wave of infections, scientists are optimistic that broad vaccination coverage should provide significant protection against severe illness and death. Data from all three countries shows at-risk groups that were given priority for vaccination are for the most part staying disease-free.
Israel has so far given at least one dose of vaccine to 62% of its population, the U.K. to 48% of its residents and Chile to 40%, according to health ministries and data compiled by the University of Oxford’s Our World in Data project.
The U.S. has administered one shot or more to 39% of its population and the 27 members of the European Union have together vaccinated just 18% of theirs.
Israel offers a lesson in what happens if vaccination outpaces the virus. The country was averaging more than 8,000 new infections a day at the peak of its last big wave in mid-January. New cases now are in the low hundreds. Some Israeli hospitals, including the country’s largest, Sheba Medical Center, have begun shutting their Covid-19 treatment wards.
Residents packed into restaurants in bars as the Israeli economy reopened in March and students returned to classrooms, sparking concern another wave was imminent.
Instead, cases continued to wane, suggesting widespread immunity from vaccination or past infection is keeping a lid on the virus’s spread.
“A lot of people, including us, said it’s a possibility that we’d have another wave in March,” said Eren Segal, a computational biologist at the Weizmann Institute in central Israel and a member of a civilian advisory committee to the government on coronavirus issues. “We’re very happy it hasn’t happened so far.”
Prof. Segal said that by summer time there will be an even lower chance of a resurgence as Israel is expected to have vaccinated many of its 12-to-15-year-olds by then, further diminishing the size of the susceptible population. An extensive program of testing is aiming to keep the virus under control in younger children. Researchers now say they don’t expect any more spikes in infections unless a vaccine-resilient variant enters the country.
Chile’s vaccination campaign has been a bright spot in Latin America as its neighbors struggle to secure their own shots while being battered by a second wave of infections.
But the country is wrestling with a surge of new infections that forced President
government to implement a new lockdown, close the borders, and postpone elections that were scheduled for this month. New coronavirus cases rose above 9,000 a day this month, the highest daily total, pushing hospitals to capacity with an influx of younger patients.
Health experts say the rise in infections highlights the risk of easing social restrictions before enough people have been inoculated to prevent the virus spreading, and the threat of variants such as P.1, first identified in Brazil.
Some epidemiologists say Chile was too quick to celebrate its rapid vaccination rollout. As officials eased restrictions, residents lowered their guard on measures such as mask-wearing, hand washing and social distancing, believing the pandemic would soon be over, said Claudia Cortés, an infectious disease expert at the University of Chile.
“They gave the wrong message,” she said. “For the general population, it was very confusing.”
Chile has also relied heavily on China’s Sinovac vaccine, which Chile’s government said last week was only 16% effective in reducing the risk of infection after one shot and 67% effective two weeks after the second dose.
Officials and doctors say the vaccines are starting to deliver results. While cases surge among people under 60 years old, infections are beginning to decline for the high-risk elderly, whose deaths have leveled off, according to government data. The two-dose regimen is 80% effective in preventing death from Covid-19, the government said.
“There is now a clear trend that we can see with the separation of the curves among those older than 70 and younger people, who are just starting to be vaccinated,” said Miguel O’Ryan, public-health expert at the University of Chile.
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U.K. officials, who are wrestling with vaccine-supply issues as they chart a route out of a strict lockdown needed to control the contagious B.1.1.7 variant first detected in England, see Chile’s experience as a cautionary tale. The country has suffered the highest death toll in Europe and scientists and public-health experts advising the government are urging a slow and gradual release of restrictions to ensure vaccinations keep outpacing the virus.
Disease modelers advising the U.K. government have analyzed the possible course of the pandemic over the next year if restrictions on the economy and daily life are eased in line with Prime Minister
four-step road map out of lockdown.
Their work highlights the risk of an exit wave, with one model by epidemiologists at Imperial College London suggesting the U.K. could face another five million cases through June 2022 if controls are relaxed as planned. That is more than the four million known cases already recorded, though gaps in testing early in the pandemic mean the true total of infections is likely far higher.
Vaccination means hospitalizations and deaths from Covid-19 are likely to be much lower than in previous surges of the pandemic, according to the models. But they are still substantial, with Imperial’s model, for instance, pointing to as many as 15,700 more deaths through June 2022. So far, the U.K. has suffered 150,000 deaths with Covid-19 mentioned on the death certificate.
A panel of scientists that advises the government said in a report that the size of any exit wave will be enormously sensitive to issues including the speed and level of vaccine uptake, any supply hiccups and the still-uncertain role that warm weather and summer behavior play in limiting the virus’s spread.
Another critical factor is how effective the vaccines are at stemming transmission, beyond just preventing infection or severe illness.
A vaccine that is highly effective at stopping transmission would likely mean far fewer cases and very few deaths, said Prof. Medley, who sits on the advisory panel.
Scientists are still collecting data on the effect of vaccines on the virus’s spread. Studies from Israel and the U.K. suggest the vaccine developed by
is highly effective at preventing onward transmission.
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