NEW YORK (NYTIMES) - After Dr Sheila Katz's husband died of a degenerative nervous system disorder in April, she knew she had to get away. But her husband had been her travel partner, and without him, she was hesitant to travel alone.

The Covid-19 pandemic's ever-shifting travel regulations were intimidating as well.

So Dr Katz, 45, did something she had never done before: She joined a group tour.

"I wanted to not be totally alone, but also to be able to do my own thing when I wanted," she said.

So in July, she joined a group of 17 fully vaccinated travellers heading to Belize with EF Go Ahead Tours, making friends as she snorkelled, visited Mayan ruins and took chocolate- and tortilla-making classes.

Solo travellers like Dr Katz are joining guided tours at unprecedented rates, said tour organisers, with some companies reporting single bookings up 300 per cent over those from couples, families or clusters of friends.

The majority of these lone travellers have never taken a group trip before.

After years of planning their own trips and travelling solo or with a partner, the Covid-19 pandemic - with its months of isolation and its travel rules for testing, masks and vaccination - has pushed them to change their ways.

Dr Katz, a sociology professor at the University of Houston, had just endured the tenure-review process while also navigating her grief. She was exhausted and had no interest in parsing border regulations or stressing out about potential exposure to the coronavirus.

For her trip to Belize, everyone in the group had to be vaccinated, which lifted a proverbial weight from her shoulders.

"Had it not been a pandemic, I probably would have just gone to lie on a Caribbean beach for seven days," she said.

The National Tour Association (NTA), a professional organisation for tour operators, said the group travel industry as a whole has yet to recover from the pandemic's blow to its business.

"Half of our tour operators don't expect their company to outperform 2019 metrics until 2023," said Mr Bob Rouse, NTA's vice-president of communication.

But even before the pandemic, group travel was gaining a foothold among two key demographics: women and millennials.

Travel companies catering specifically to women have increased by 230 per cent over the past six years, while a flurry of new travel start-ups, including AvantStay and Trips by the Culture Trip, have grown by marketing towards those born after 1980.

Women's interest in group travel is, perhaps, most notable.

Ms Katalina Mayorga, chief executive of El Camino Travel, which offers small group tours for women, said that sales for the fourth quarter of this year are 200 per cent higher than the same period in 2019, and 65 per cent of those booking are doing so as solo travellers.

Contiki's customers skew 60 per cent female.

Ms Allison Scola, founder of Experience Sicily, says solo women on her tours now make up 66 per cent of guests, while at Indus Travels, 80 per cent of customers booking spots on tours for solo travellers are now women. Ninety per cent of Indus' customers this year are booking for the first time.

"Even solo travellers want to travel with people, sometimes, especially people who they have something in common with," said Ms Amanda Black, founder of The Solo Female Traveller Network, where women can book individual tickets for group trips across the globe.

Ms Black, 35, restarted her tours in May after shutting down at the start of the pandemic, and said bookings have been steadily climbing.

"It's almost as if the difficulties of travelling during the pandemic have helped millennials get over the idea that group tours aren't cool," said Ms Tara Cappel, founder and chief executive of FTLO Travel, where bookings for next year are up 225 per cent over 2019.

FTLO caters to 20- and 30-somethings, and first-time customers - many of them joining solo - comprise 82 per cent of those bookings; 75 per cent of travellers booking for next year are women.

In many cases, the shift to millennial-focused marketing is redefining the idea of what it means to travel on an organised tour in the first place.

"It was really intimate, and we kind of just looked like some friends who were travelling," said Ms Autumn Lewis, a lawyer in Los Angeles who took her first-ever group tour, a trip to Greece run by Tripsha, in July.

US Tour Operators Association president and CEO Terry Dale said: "If there's one thing the pandemic has shown us, it's that the value of tour operators has increased tenfold."

Like travel agents, who are also enjoying a resurgence in popularity, much of that value comes when a traveller can delegate the pandemic mental load: Which vaccine card is valid? On which day do I need to take my polymerase chain reaction test?

But after months of isolation, the group tour's strongest draw may be its most obvious: It comes with a built-in community.

Dr Katz, for instance, had expected that for some meals on her tour, people would go off and do their own thing. She was wrong.

"Our tour guides had to go out of their way because we all wanted to have all of our meals together," she said. "I think we were all just so thankful to not be in our living rooms, staring at the wall."