Young adults are the biggest source of Maryland COVID cases. Officials say it’s critical that more of them get vaccinated.

They had Zoom calls all winter, moved outdoors when it got warmer and now, occasionally, go to public places so long as there is outside seating and there aren’t big crowds.

But Monica Duro, a 24-year-old Odenton woman, and her friends know other young adults no longer take so many COVID-19 precautions. Lifting restrictions on bars and restaurants likely sent a message about “normalcy,” she said.

“We may need a moment for a reality check,” Duro said. “We are still in a pandemic and we need everyone to be vaccinated first.”

Duro got her second COVID-19 shot Tuesday at the M&T Bank Stadium mass vaccination site, which has been, in addition to regular appointments, hosting “university days” with doses set aside for students and employees.

That’s part of the state’s “No Arm Left Behind” campaign, and public health officials say such efforts are crucial to reaching President Joe Biden’s goal of getting 70% of the nation at least partially vaccinated by July 4. But more immediately, the move is needed to stem infections among those age 18-49 — especially those 20-29, who make up the biggest share of infections in Maryland.

Young adults and children are far less likely than older adults to get severely sick or die from COVID-19. But the increase in cases, many caused by variants, are leading to more reports of serious illness. Six people in their 20s died in Maryland from COVID during the last 10 days of April alone. And case rates for children have doubled since March, according to state figures.

The trend is a national one. Federal figures show those ages 18-49 now make up the biggest share of hospitalizations in 14 states, including Maryland.

The numbers are unlikely to abate until many more of the state’s younger residents get vaccinated. State data shows more than 80% of those 65 and older have been at least partially vaccinated while fewer than half of those ages 18 to 49 have gotten a shot. Both the Pfizer/BioNTech and Moderna vaccines require two shots.

“The virus is going to continue to spread among unvaccinated people,” said Matthew Frieman, associate professor in the department of microbiology and immunology at the University of Maryland School of Medicine. “The more people we have [vaccinated], the slower that spread.”

The cases among young people are particularly pronounced in Baltimore, where cases rose to exceed last winter’s peak before receding in mid-April. But the city’s rate remains the worst in the state at almost 3 cases per 1,000 people in the past two weeks. Baltimore and Dorchester counties are on its heels.

There have been a total of almost 103 infections per 1,000 people in their 20s and 30s in Baltimore, while the city’s overall rate is about 87 infections per 1,000 people.

The average age of infection in Baltimore is now 36, four years younger than it was in January and 10 years younger than a year ago.

City health officials have turned to memes and sassy tweeting about vaccines that are likely to get the attention of younger followers, though Adam Abadir, a health department spokesman, said the tweets weren’t meant to be age-specific.

Many people get their information online now, he noted, and “we want to be part of those online conversations.”

The city and other public health officials are working to maintain vaccine demand, which dropped off by nearly 25% nationwide during the last week of April, according to a review by the Kaiser Family Foundation. In Maryland, demand dropped 11.5%, more in line with Delaware and Washington, D.C., than some Southern states.

Several younger adults and teens getting vaccinated at M&T Bank Stadium on Tuesday said they needed no extra prodding and came for a shot as soon as they became eligible. The state mass sites now allow people to make appointments or walk up for a shot.

And now that the vaccines are more easily accessible in mass sites, as well as pharmacies, some physicians’ offices and elsewhere, Duro, the Odenton woman, thought bars and restaurants and other public places should consider requiring proof of vaccination so everyone inside can feel safe.

“I’ve been wearing two masks and doing a lot of socializing virtually and at a distance,” said Cori White, a 35-year-old who drove from Montgomery County to Baltimore for her second shot.

“I knew we were getting close to ending this [pandemic] and I didn’t want to mess anything up,” she said. “Most of my friends are the same way, but a few have wanted to go do stuff that was clearly unsafe and I graciously said, ‘No thank you.’ ”

Tim Zhang, a 39-year-old from Catonsville, said he has been looking forward to his second vaccination so he and his wife could “get our freedom back” and visit their vaccinated parents without strict safety measures.

Shiloh Burke, a 17-year-old from Silver Spring, said her motivation in addition to more freedom to see friends is making lacrosse practice “less nerve-wracking.” And once her 12-year-old brother is vaccinated, the whole family can spend more time with her grandparents.

She said it won’t matter if she follows all the rules if others don’t, and sometimes teens and young adults don’t.

“They want to do what they want to do all the time and don’t take things as seriously,” she said.

And when they get infected, they are perpetuating the pandemic, said Jennifer Nuzzo, an epidemiologist and a senior scholar at the Center for Health Security in the Johns Hopkins University’s Bloomberg School of Public Health.

“We know younger people are more susceptible to transmission because they are going out more,” she said during a recent forum on the virus. “It’s so critical when we’ve protected the most at-risk to vaccinate younger adults because of the role they play in the overall transmission.”

She said every time someone goes to a crowded place unvaccinated and without precautions, it’s an opportunity for spread. And that means more cases, hospitalizations and deaths among younger people, which she said is a “tragedy because we can prevent it.”

More young people are coming in for shots at the M&T site, particularly college-age students as several universities have required vaccination for fall attendance, said Dr. Chirag Chaudhari, an emergency physician at the University of Maryland Medical System and the medical director at the M&T site, which is operated by the medical system and the state.

Chaudhari said he hopes increased interest will stem cases among young adults and teens, which he saw rise somewhat after spring break. He said the site is preparing to vaccinate those aged 12-15, who are expected to become eligible for the Pfizer vaccine in the next week.

“At the hospitals unfortunately, while the overall number of COVID cases are declining, we’re seeing a flip and an increase in the percentage of cases in 20- and 30-year-olds, including some on ventilators,” he said. “Many don’t have preexisting conditions.”

He said people likely have gotten comfortable after seeing the overall state and federal case number come down since a peak in mid-January, but he urged them to remain vigilant until they are fully vaccinated.

Younger people “are a critically important part of us getting to enjoy our summer with friends and loved ones and going back to a time we used to know pre-COVID,” he said. “We need their participation.”