A monoclonal antibody cocktail developed by the drug maker Regeneron offered strong protection against Covid-19 when given to people living with someone infected with the coronavirus, according to clinical trial results announced on Monday. The drug, if authorized, could offer another line of defense against the disease for people who are not protected by vaccination.
The findings are the latest evidence that such lab-made drugs not only prevent the worst outcomes of the disease when given early enough, but also help prevent people from getting sick in the first place.
Using the cumbersome drugs preventively on a large scale won’t be necessary: Vaccines are sufficient for the vast majority of people and are increasingly available.
Still, antibody drugs like Regeneron’s could give doctors a new way to protect high-risk people who haven’t been inoculated or who may not respond well to vaccination, such as those taking drugs that weaken their immune system. That could be an important tool as rising coronavirus cases and dangerous virus variants threaten to outpace vaccinations.
Regeneron said in a news release that it would ask the Food and Drug Administration to expand the drug’s emergency authorization — currently for high-risk people who already have Covid but are not hospitalized — to allow it to be given for preventive purposes in “appropriate populations.”
There’s “a very substantial number of people” in the United States and globally who could be a good fit to receive these drugs for preventive purposes, said Dr. Myron Cohen, a University of North Carolina researcher who leads monoclonal antibody efforts for the Covid Prevention Network, a National Institutes of Health-sponsored initiative that helped to oversee the trial.
“Not everyone’s going to take a vaccine, no matter what we do, and not everyone’s going to respond to a vaccine,” Dr. Cohen said.
Regeneron’s new data come from a clinical trial that enrolled more than 1,500 people who lived in the same household as someone who had tested positive for the virus within four days. Those who got an injection of Regeneron’s drug were 81 percent less likely to get sick with Covid compared to volunteers who got a placebo.
Dr. Rajesh Gandhi, an infectious diseases physician at Massachusetts General Hospital who was not involved in the study, said the data were “promising” for people who have not yet been vaccinated. But he said that the study did not enroll the type of patients that would be needed to assess whether the drug should be used preventively for immunocompromised patients. “I would say we don’t yet know that,” Dr. Gandhi said.
Regeneron’s cocktail, a combination of two drugs designed to mimic the antibodies generated naturally when the immune system fends off the virus, got a publicity boost last fall when it was given to President Donald J. Trump after he got sick with Covid.
The treatment received emergency authorization in November. Doctors are using it, as well as another antibody cocktail from Eli Lilly, for high-risk Covid patients.
But use of the antibody drugs has been slowed not by a shortage of doses, but by other challenges, though access has improved in recent months. Many patients don’t know to ask for the drugs or where to find them.
Many hospitals and clinics have not made the treatments a priority because they have been time-consuming and difficult to administer, in large part because they must be given via intravenous infusion. Regeneron plans to ask the F.D.A. to allow its drug to be given via an injection, as it was administered in the results of the study announced on Monday, which would allow it to be given more quickly and easily.
Britain reopened large parts of its economy on Monday, allowing people in England back in shops, hair salons and outdoor areas of pubs and restaurants, a long-awaited milestone after three months of lockdown, and a day after the country recorded its lowest daily coronavirus death toll since September.
Under the second stage of the government’s gradual reopening, libraries, community centers and some outdoor attractions like zoos will also return, though outdoor gatherings remain limited to six people or two households.
For many in England, the return was a hopeful — if not definitive — sign that the worst of the pandemic was behind them, after a new variant of the virus detected last year in the country’s southeast spun out of control around Christmas, overwhelming hospitals and causing tens of thousands of deaths.
At its winter peak, Britain reported as many as 60,000 daily cases a day and 1,820 daily deaths, according to a New York Times database. But after months of restrictions and an aggressive vaccination program that has offered a dose to about half of Britain’s population, those figures declined to 1,730 daily cases and seven deaths reported on Sunday.
Prime Minister Boris Johnson has so far gone ahead with the gradual easing of measures that he had announced, reopening schools on March 8, reducing restrictions on outdoor gatherings on March 29, and allowing large parts of the economy to reopen on Monday.
Mr. Johnson said on Monday that the reopening was “a major step forward in our road map to freedom.” Still, he urged caution.
“I urge everyone to continue to behave responsibly and remember ‘hands, face, space and fresh air’ to suppress Covid,” he said.
Scotland, Wales and Northern Ireland, where devolved governments are responsible for coronavirus restrictions, have laid out similar plans to reopen their economies.
The apparent success represents a turnaround for Mr. Johnson’s government, which struggled to stem cases earlier in the pandemic and at one point reported the greatest rate of excess deaths in Europe.
But now E.U. countries — hampered by a vaccine rollout slower than Britain’s and a scare over a possible links between the AstraZeneca vaccine and blood clots — are facing a third wave of coronavirus infections. France, Italy and other countries have recently imposed new lockdown measures.
In England, business owners reopened on Monday with hope — and some anxiety that the numbers of infections could go up again. Still, “we’re looking confident we won’t be seeing anything like that again,” said Nicholas Hair, the owner of The Kentish Belle, a London pub that opened its doors to patrons one minute after midnight.
Australia has given up on the goal of vaccinating its entire population against Covid-19 by the end of the year, following updated advice from health officials that younger people should not receive the AstraZeneca vaccine, as well as delays in the delivery of doses.
The Australian government said last week that it had accepted a recommendation by a panel of health experts that people under 50 receive the Pfizer-BioNTech vaccine instead of the one developed by AstraZeneca, which had been the centerpiece of Australia’s vaccination program. The change in guidance came after European regulators found links between the AstraZeneca vaccine and rare blood clots, prompting several countries to restrict use of the shot.
Prime Minister Scott Morrison said Friday that the government had ordered another 20 million doses of the Pfizer vaccine, doubling what it had already purchased. But they are not expected to be available until the fourth quarter of this year, dealing a blow to the government’s previously stated goal of inoculating all of its 25 million people by then.
Mr. Morrison appeared to acknowledge the change in timeline in a Facebook post on Sunday.
“The government has also not set, nor has any plans to set any new targets for completing first doses,” Mr. Morrison said. “While we would like to see these doses completed before the end of the year, it is not possible to set such targets given the many uncertainties involved.”
Public health experts have criticized Mr. Morrison’s government for relying too heavily on the AstraZeneca vaccine, a relatively cheap and easy-to-use shot but one whose troubles have jeopardized inoculation efforts in multiple countries. They said the setback to Australia’s vaccination program risked undermining the country’s success in containing the spread of the coronavirus since recording its first case in January 2020.
“We’re in a position a year later where that hard-won success is jeopardized by a completely incompetent approach to a vaccine rollout,” said Bill Bowtell, a public health policy expert and adjunct professor at the University of New South Wales in Sydney.
Australia has made four separate agreements for the supply of Covid-19 vaccines that would give it a total of 170 million doses, enough to inoculate its population more than three times over. Plans to manufacture almost all of its 54 million AstraZeneca doses domestically were approved last month.
But the Australian government has been under fire for weeks over the sluggish pace of its vaccination rollout, which began in late February. By the end of March, when the government had aimed to vaccinate four million people, only about 600,000 had actually been inoculated. As of Sunday, Australia had administered fewer than 1.2 million doses.
Australian officials have attributed the slow rollout to delays in the delivery of millions of vaccine doses manufactured in the European Union, which has curbed exports amid its own supply shortages. The export restrictions mainly affect the AstraZeneca vaccine.
After enduring strict lockdowns for much of the past year, Australians are now enjoying relatively normal life in a country that has all but stamped out the virus. But public health experts warn that until more of the population is vaccinated, those freedoms are precarious.
“Having eliminated Covid, they thought a mass vaccination campaign would lock that in,” Mr. Bowtell said of the Australian public. “Now they are being deeply disillusioned.”
Thailand is facing its worst coronavirus outbreak just as millions of people head to their home provinces during the country’s biggest travel holiday.
The latest wave of infections, which has sent at least eight cabinet members into isolation, is centered in a Bangkok nightlife district said to be popular with government officials and wealthy partygoers. The country, which until now has largely kept the virus under control, set a record Monday for new daily cases with 985.
One top health official warned that Thailand could soon face as many as 28,000 new cases a day in the worst-case scenario. The government announced it would set up field hospitals as Covid-19 wards at existing facilities begin to fill up.
Officials ordered the closure of hundreds of bars and nightclubs, but critics say the government has been inconsistent in its efforts to bring the outbreak under control. The prime minister, Prayuth Chan-ocha, stopped short of banning travel between provinces for the Songkran holiday, which begins on Tuesday and marks the beginning of the Thai New Year.
“Whatever will be, will be,” he said last week in explaining his decision. “The reason is it’s a matter that involves a huge number of people. The government will have to try to cope with that later.”
Dozens of provinces have imposed their own restrictions on travelers coming from Bangkok and other affected areas, prompting many Thais to cancel their trips. But many others set off over the weekend.
During earlier outbreaks, the government often acted quickly to require face masks, ban foreign tourists, impose quarantine restrictions and lock down hard-hit areas. It has reported fewer than 34,000 cases — mostly from a January surge traced to a seafood market near Bangkok — and just 97 deaths.
But it has been lax in testing and slow to vaccinate. So far, it has procured about 2.2 million doses and given at least one to about 500,000 people. Thailand’s population is 70 million.
Vaccine production is not expected to begin in earnest until June, when a manufacturer in Thailand is scheduled to begin producing 10 million doses a month of the AstraZeneca vaccine.
Health officials were alarmed by the recent discovery of dozens of cases of the highly infectious coronavirus variant first identified in Britain. The finding highlighted the inadequacy of Thailand’s virus testing and suggested that its quarantine procedures have not been as effective as officials believed.
Tourism operators have been especially angered by the government’s lackadaisical approach to obtaining vaccine supplies. The tourism industry, which normally accounts for about 20 percent of the nation’s economy, is highly dependent on foreign visitors and has been calling for widespread vaccinations to speed its recovery.
The outbreak in Bangkok has also prompted questions about the activities of some top officials and their aides.
The transportation minister, Saksayam Chidchob, who was hospitalized with Covid-19, was criticized for not being forthcoming about his whereabouts during times when he may have been exposed to the virus. He denied visiting the gentlemen’s club at the center of the outbreak and said he believed he had contracted the virus from an aide.