Bat mitzvah ceremonies and bachelor parties are hastily scaled back. Wedding planners watch their head counts plummet. Long-awaited amateur sports events and dream trips abroad are called off.

As coronavirus cases explode in the U.S., health experts and government officials are struggling to confront a pandemic that has already killed more than 5,000 and sickened more than 100,000 across the globe. Last week saw a decisive shift toward more serious containment measures, with mass school closures, a ban on travel from Europe and a national emergency declared by President Trump.

But as Americans begin to come to terms with the threat posed by the virus and the deadly lung disease, covid-19, that it causes, another spectacle is playing out: countless plans and personal milestones rendered impossible by new restrictions on human contact. In a society retreating upon itself to prevent or forestall infection, the cherished rituals that define life are evaporating.

The stakes of a postponed party or religious ritual are small when set beside the extreme health risks posed to the vulnerable by covid-19. But those individual disappointments nevertheless provide a preview of how people cope with what public health experts say could be more serious disturbances that await — and of human adaptability and cooperation in the face of large-scale disruption.

“To know that these huge rites of passage are going to be compromised by this is a big deal for families,” said Jennifer Oko, whose daughter’s bat mitzvah — scheduled for next month — appears likely to be upended by newly imposed limits on gatherings at her synagogue, Temple Micah, in Northwest Washington. Nevertheless, she acknowledged, “our own little personal tragedy about the impact on the bat mitzvah just feels really small compared to the rest of the world.”

As a consultant in the health sector, Rachael Fleurence — a Bethesda resident who also attends Temple Micah — knew that severe changes to daily life from the novel coronavirus were only a matter of time. But she had hoped her daughter Elodie’s bat mitzvah, scheduled for Saturday, might still go forward as planned before containment measures went into effect.

“The world changed very quickly,” she said. “I knew this was coming for a while, but I thought we might kind of scrape by. And then we didn’t.”

On Tuesday, after conferring with her rabbi, she decided to proceed with the formal portion of the Jewish coming-of-age ritual while canceling the traditional reception and celebration that follow. On Thursday, they agreed to overhaul the event completely.

Now nobody will attend except Elodie’s parents and brother, as well as the rabbi and two other temple officials. The ceremony will be live-streamed to other members of the synagogue, who plan to watch and congregate virtually with a special Slack channel set up for the occasion.

“This has been hard on my daughter, who’s been preparing for six months. And we’ve had the date for three years,” Fleurence said. “But it’s the right thing to do.”

Postponing a bar or bat mitzvah is practically impossible: The events are booked years in advance, and children spend months studying to recite a specific section of scripture chosen according to the date of the ceremony. Similar problems arise in other religious faiths, where many important observances follow a rigid calendar.

That is true for Christians, especially Catholics, who find the coronavirus outbreak coinciding with the run-up to Easter. The Rev. John Barry of the Church of the Resurrection in Burtonsville, Md., said First Reconciliation — the precursor to First Communion, in which children confess privately to a priest for the first time in their lives — had been scheduled for Saturday.

About a week ago, he said, church officials decided to call off the reception that typically follows the momentous event in the spiritual lives of young Catholics. Then, on Thursday, the event was postponed until later in the year. A new date has not been set, but it must take place before First Communion, which is typically held in April or May — assuming that public gatherings are again feasible by then.

“They got their hopes up for it,” Barry said of the children in his parish. “They’re going to remember this. They’re going to remember that this happened to them as a kid when they get older.”

The coronavirus is also wreaking havoc with more secular rites of passage.

Justin Kincaid, a 35-year-old Alexandria resident, had looked forward to the bachelor party he planned with about a dozen friends: They would rent a house, complete with a bar and indoor pool, in the mountains outside Denver. The trip was to coincide with the “Elite 8” round of the NCAA college basketball tournament — TV entertainment for the group when they weren’t on the ski slopes or out on the town in Denver.

Now the NCAA tournament has been canceled, and Kincaid has seen half of his friends pull out as people curtail their air travel plans.

He is thinking about booking a smaller place for the remaining people who want to hold the party but is worried about making any plans as the virus continues to spread and countermeasures evolve hour to hour. On Thursday, Trump said he would not rule out restrictions on domestic travel.

“There’s no point in setting something else up and then we get a full lockdown,” Kincaid said. “We also have to consider: Is there going to be anything to do? I don’t know if you’re going to be able to go skiing by that time. I don’t know if the restaurants and bars are going to be up and running.”

He said he and his fiancee are also beginning to worry about whether their May wedding can proceed.

Janay Watson, a graduate student at Georgetown University, has already been forced to cancel an eagerly awaited trip. Watson, who said she was the first in her family to obtain a master’s degree, was planning to join a university trip to South Africa in the coming months.

She also booked tickets immediately before and afterward for Italy and Brazil — a kind of cross-continental grand tour, in late April and early May.

“I really wanted to do it big and go around the world,” she said.

When the university called off the South Africa trip and travel to Italy — the most severely virus-afflicted country outside China — became impossible, Watson had to abandon her carefully planned voyage. She said she lost about $2,000 that the airlines would not refund.

For Tucker Cholvin, the loss from new virus-related restrictions was less tangible. The 27-year-old District resident had trained hard for half-marathons this summer, including the New York City Half Marathon scheduled for Sunday. The event was called off last week, as was another he planned to enter in Delaware next month.

“It’s tough,” he said. “I’ve put a lot of hard work into this, and I’ve been running faster than ever. And suddenly I feel like my entire summer has been yanked.”

Cholvin said he hopes to enter other races later in the year, including a full marathon, “assuming society returns.”

In the meantime, he said, the uncertainty is unsettling — as is the fear that the sudden disruptions that greeted him and many others this week herald more disturbing changes to daily life that nobody can yet foresee.

“When cancellation after cancellation starts coming in,” he said, “you start to wonder . . . what else is next?”