Omicron Can Weaken Vaccines, but Boosters Show Promise, U.K. Study Says

A third dose of the Pfizer-BioNTech vaccine, though, lifted the figure to roughly 75 percent.

Two doses of the AstraZeneca vaccine appeared to offer virtually no protection against symptomatic infection caused by Omicron several months after vaccination. But for those recipients, an additional Pfizer-BioNTech dose paid big dividends, boosting effectiveness against the variant to 71 percent.

Still, the study’s authors said they expected that the vaccines would remain a bulwark against hospitalizations and deaths, if not infections, caused by Omicron. And the researchers cautioned that even in a country tracking the variant as closely as Britain is, it was too early to know precisely how well the vaccines would perform.

That study was released alongside new findings about how easily Omicron is managing to spread. Someone infected with the Omicron variant, for example, is roughly three times as likely as a person infected by the Delta variant to pass the virus to other members of his or her household, Britain’s Health Security Agency reported.

And a close contact of an Omicron case is roughly twice as likely as a close contact of someone infected with Delta to catch the virus.

Neil Ferguson, an epidemiologist at Imperial College London, said that Omicron’s ability to evade the body’s immune defenses accounted for most of its advantage over previous variants. But modeling work by his research team also suggested that Omicron was simply more contagious than Delta, by roughly 25 to 50 percent.

“I think that there’s a significant amount of immune escape,” Dr. Ferguson said, referring to the virus’s ability to dodge the body’s defenses. “But it’s also more intrinsically transmissible than Delta.”

He and other scientists have cautioned that evidence was still coming in, and that better surveillance in places where the Omicron wave is most advanced could affect their findings.

The World Health Organization said this week that some evidence had emerged that Omicron was causing milder illness than Delta, but that it was too early to be certain. Still, scientists have warned that if the variant keeps spreading as quickly as it is in England, where cases are doubling every 2.5 days, health systems around the world may be deluged with patients.

Even if Omicron causes severe illness at only half the rate of the Delta variant, Dr. Ferguson said, his computer modeling suggested that 5,000 people could be admitted to hospitals daily in Britain at the peak of its Omicron wave — a figure higher than any seen at any other point in the pandemic.

Scientists said that widespread vaccination in countries like Britain and the United States would keep as many people from dying as have in earlier waves. But the experts also warned that patients with Covid and with other illnesses would suffer if hospitals became too full.

“It only requires a small drop in protection against severe disease for those very large numbers of infections to translate into levels of hospitalization we can’t cope with,” Dr. Ferguson said.

It will take several weeks to understand how the current surge in Omicron infections may translate into people needing hospital care. “I’m concerned that by the time we know about severity,” Dr. Ferguson said, “it may be too late to act.”

The potential for a surge in hospitalizations was thrown into sharp relief by the modeling study released on Saturday, created by a separate group of experts at the London School of Hygiene & Tropical Medicine. For now, those scientists assumed that Omicron would cause disease just as severe as Delta does in unvaccinated people, but also that mounting levels of immunity from vaccinations and previous infections would temper the Omicron wave, as has happened in South Africa.

In the scenario that some outside experts said was most likely — in which Omicron evaded people’s immune defenses to a large degree, but booster doses also proved highly effective — the scientists said that England could be hit hard. Through April, they predicted roughly 300,000 hospitalizations and 47,000 deaths.

That could place a bigger daily burden on English hospitals at the peak of the Omicron wave than was seen at any time earlier in the pandemic.

Crucially, the scientists said that reintroducing certain restrictions could save thousands of lives and spare tens of thousands of people hospital stays.

Outside experts emphasized that Omicron remained poorly understood, that people may be able to fight off severe infections more effectively than the models predicted, and that the arrival of new antiviral pills in the coming months could soften the blow of infections.

Still, scientists urged governments to speed up inoculation campaigns, share doses with less-vaccinated nations and consider measures like more self-testing, if not new restrictions.

“The coronavirus has not finished with us,” said Michael Head, a senior research fellow in global health at the University of Southampton in England.

“A tactic of ‘turning the lights off and pretending we are not in’ is a failed policy.”

The International Council of Nurses, whose member associations represent more than 27 million nurses, said there was already a global shortage of around six million nurses at the start of the pandemic. That figure could double in the next few years, the group said, as nurses retire or flee the profession. Mr. Catton suggested that the impact of another worldwide coronavirus wave could leave the global health care industry trying to find replacements for close to half its existing work force.

A W.H.O. paper in September estimated that more than 115,000 health care workers had died from Covid-19, but Mr. Catton said that number was based on data from a limited amount of countries and a limited period of time, and may represent only half the real toll.

And there are other factors fueling attrition among health care workers, Mr. Catton said, from grueling working hours and conditions, to lack of personal protective equipment and vaccines, and verbal abuse and even physical attacks by distraught relatives.

Mr. Catton said he had spoken to nurses who feel they “have run two, three or even four marathons with each wave of the pandemic.” Many, he said, are not sure that they can face the physical and emotional toll of another wave with Omicron.

The increase in Omicron cases has Europe on edge. Britain instituted a “Plan B” that involved encouraging people to work from home and introducing a passport requirement for certain indoor venues. France closed its nightclubs for four weeks but rejected other restrictions, and Germany mandated vaccinations for health care workers. The measures have helped rekindle a debate over civil liberties on the continent.

Concerns about the balance of safety and freedom were also expressed in South Korea, where protests were held over rules requiring vaccine passes in many educational settings.

Here’s what else happened this week:

• The Food and Drug Administration authorized boosters of the Pfizer shot for 16- and 17-year-olds, as well as an AstraZeneca drug designed to protect people with compromised immune systems. A study from the Centers for Disease Control and Prevention found that protection provided by the mRNA vaccines waned for some older adults.

• All three of President Biden’s vaccine mandates for the private sector have been put on hold by the courts, and the Senate voted symbolically to eliminate Mr. Biden’s mandate for large employers. The Pennsylvania Supreme Court struck down a mask mandate for K-12 classrooms, but Chief Justice John G. Roberts Jr. allowed the mask mandate for air travel in the United States to stand. Stricter testing requirements for travelers entering the country took effect.

• As legions of people suffer from losses caused by the pandemic, a new name was introduced for the endless cycle of mourning that some people experience: prolonged grief disorder. The U.S. surgeon general, Dr. Vivek H. Murthy, warned that the pandemic was intensifying a mental health crisis among young people.

• The National Guard has been asked to aid hospitals in at least four states as the latest surge of cases puts strain on health care resources.

• More than 200 million Americans have been fully vaccinated, which is over 60 percent of the population, and the federal government said it would invest $400 million in a program to help other countries vaccinate their citizens. Still, as the United States and other wealthy nations raced to distribute boosters, the World Health Organization warned that their efforts could damage global vaccine equity.

• In New York City, Mayor Bill de Blasio announced a vaccine mandate that covers all private employers. The man who will succeed him in less than a month, Eric Adams, did not commit to enforcing the rule. Starting on Monday, New York State will require masks in all indoor public spaces where vaccinations are not mandated.

Some destinations, including the United Kingdom and certain European Union countries, require travelers to complete a digital passenger locator form before entering the country (you must submit the U.K. form in the 48 hours before you arrive in the country), to help with contact tracing.

Coronavirus test results

More countries now require proof of a negative test, often in addition to proof of vaccination. Depending on where you are going, some countries require P.C.R. tests, while others allow rapid antigen tests. The timing requirement of your test might ask for results between 24 or 72 hours before your arrival, or one to three days.

Masks

Mask mandates too vary by country and maybe localities, but you will most certainly need masks in airports, on your flight — and if you are going to most places in Europe and the U.K., for indoor activities like dining. And rather than hoping your cloth mask will have you covered, come prepared with surgical masks and N95s as well.

Proof of insurance

Not only is it a good idea to check your health-insurance policies if you get sick abroad, you should research whether proof of health or travel insurance is needed at your destination.

Test for your return trip

All travelers, vaccinated or not, wishing to fly into the United States from abroad are currently required to show proof of a negative coronavirus test — specifically, a rapid antigen or P.C.R. test — taken within one day of their flight.

Defenders of vaccine passes point out that they drove up the vaccination rate in France, another country that jealously guards rights. But to critics, the targeted nature of these restrictions imposes a stigma on one part of society. That carries disquieting echoes in Germany and Austria, where right-wing protesters invoke the Nazi boot to claim that the state is persecuting those who resist vaccines.

“It’s polarizing and divisive in the sense that it creates a society of us versus them, which is a very dangerous proposition, I think,” said Clifford Stott, a professor of social psychology at Keele University in England. “We are creating a recipe for disorder by amplifying structural inequalities.”

Ms. Lawson said on Twitter that she was concerned on Monday morning when she saw someone flying a drone over her house and saw a white vehicle parked outside. That evening, when she left the law firm where she works, her concern turned to terror, she said.

Four men hopped out of the white S.U.V. with cameras and recording equipment and confronted her as she tried to get into her car, she said. Her spokesman said they announced themselves to her as being with America’s Frontline Doctors, and they had the group’s logos on their jackets and microphones.

In her Twitter thread, Ms. Lawson said that members of the group, when contacted by law enforcement, had indicated they just wanted to interview her for a video they were producing. Ms. Lawson said that the group never contacted her for an interview.

“Instead, they ambushed me in a dark parking garage when they suspected I would be alone,” she wrote.

In a statement, Ms. Lawson, a former mayor of Walnut Creek, which is in the Bay Area about 15 miles east of Oakland, described herself as the daughter of a physician who believes in robust public dialogue but that the group’s behavior is “beyond the pale.”

“As a mother, I felt deeply violated and scared for my kids in our own home — and I feared for my own personal safety as a woman being surrounded by strange men in a dark parking garage,” she said.

The police said they were looking into a man who had called the department earlier in the day, claiming to be a “state detective” from Georgia who was “conducting surveillance” in the area.

Lt. Holley Connors, a spokeswoman for the Walnut Creek Police Department, said investigators believe the man was “likely involved” in the incident involving Ms. Lawson.

“At this time, there is no evidence of a crime,” she said, “but the Walnut Creek Police Department will continue to follow up on the incident.”

At the same time, vaccine misinformation spreads on TikTok and WhatsApp, and in evangelical churches where pastors warn that the shot “contains the mark of the beast.”

“No matter how educated people are, if their pastor says don’t trust the vaccine, they don’t trust,” said Dr. Morton Zuze, the clinical care coordinator at Chongwe District Hospital, where seven staff members sat idle in an empty vaccination tent.

Some Zambians are hesitant, but others have an attitude that could better be described as vaccine indifference. This is a poor country where the economy has contracted sharply during the pandemic, and many unvaccinated people are focused on putting food on the table.

“I’d like to get it but I work Monday to Saturday, and I don’t know if they vaccinate on Sunday,” said Bernadette Kawango, who supports a large extended family with her wages from an auto-parts store in a low-income neighborhood on the edge of Lusaka, the capital. Covid is not at the top of her list of health care worries. “It’s cholera season, and people have malaria, and there is H.I.V. and TB,” she said.

The pace of vaccination here is far too slow to prevent unnecessary deaths in a fourth wave already beginning in southern Africa, or to prevent the emergence of new variants such as Omicron, which was first identified in South Africa late last month. The vaccines now in stock — many of them donations close to their expiration date when they arrive — may not be used before they must be destroyed.