Correction: A previous version of this article misspelled Anuraag Routray’s last name. This version has been updated.

© Kim Raff/FTWP WEST JORDAN, UT - APRIL 17: Monica Martinez tested positive shortly after her first vaccine dose in January – but she had traveled back from the holidays and experienced symptoms the day she went to get her shot. She is photographed near her home in West Jordan, UT on Sat. April 17, 2021. (Photo by Kim Raff for The Washington Post)

Abbey Quinn regrets the Easter dinner.

The 29-year-old celebrated the holiday with her roommate’s family five days after nabbing her first Moderna vaccine shot. Later that week Quinn, a restaurant worker in Asheville, N.C., woke up feeling her shirt hurt against her skin and knew it wasn’t a typical cold.

Everyone at the meal tested positive for coronavirus, she said.

Quinn falls into an unlucky group of Americans exposed to the virus before their vaccine doses could offer them full protection. Their stories offer a reminder of the danger of people letting their guard down while highly transmissible virus variants circulate and a spring wave drives up hospitalizations across the country.

“We all had a collective, ‘Oh man, you were so close,’” Quinn recalled after telling her family about testing positive after her first shot. “I understood I wasn’t fully protected. I did feel some sense of relief not because I felt like I was immune, but just because it felt like the end was near. I saw a light at the end of the tunnel.”

There’s no clear data on how many people contracted coronavirus before their vaccinations could take full effect.

Based on a Washington Post analysis of data from the Centers for Disease Control and Prevention, The Post estimates about 21,000 of 470,000 people who tested positive for coronavirus for the week ended Sunday already had their first dose. Michigan, where cases have been rising sharply with the rise of highly transmissible variants, accounts for about a tenth of that estimate.

Experts warn these cases should not be interpreted as evidence vaccines don’t work. The immune system needs several weeks to provide robust protection as the body learns the blueprint for stopping the virus before it can cause serious disease. They are not the same as “breakthrough infections” happening at least two weeks after the final dose — which are overwhelmingly mild and extreme outliers.

With every American adult eligible for a vaccine this week, public health authorities and experts are pleading for vigilance and social distancing for a few more weeks to deliver a finishing blow to the pandemic in time for summer.

Experts say the first dose may keep coronavirus infections mild, but the protection probably wouldn’t start kicking in for at least a week. A CDC study of 4,000 vaccinated health care workers and first responders found the risk of infection was reduced by 80 percent two weeks or more after the first shot and protection increased to more than 90 percent two weeks or more after the second shot.

“Even if you develop disease, you already have a head start from an immune system standpoint on controlling the virus,” said C. Buddy Creech, the director of Vanderbilt University’s vaccine research program. “The real challenge is we have to show the blueprint to the immune system with enough lead time.”

Krutika Kuppalli, an infectious-disease doctor in South Carolina, said most patients who tested positive after a first vaccine dose that she encountered had mild symptoms.

“The thing people need to remember is the vaccine is not 100 percent protective, nothing is 100 percent protective,” Kuppalli said. “We want this to become akin to it feeling like a nuisance cold if you get vaccinated. We don’t want people having significant morbidity and mortality from covid.”

In other cases, a person may have been exposed to the virus before their first jab. Montana Gov. Greg Gianforte (R) may be among the most high-profile of those cases after experiencing mild coronavirus symptoms three days after his first shot.

Anuraag Routray, a 19-year-old freshman at the University of Texas Austin, was excited for a shot on Jan. 25 through the university. Then he felt stomach pains, which he initially chalked up to bad dorm food, and tested positive for the virus on Jan. 24.

“It felt like all the work that we had done since the pandemic begun being careful went to waste in a sense because you are so close to the vaccine, the final prize and you lose right before it,” Routray said.

Kuppalli said vaccines for other viruses, such as Ebola, have been shown to effective as a post-exposure prophylactic that could prevent disease.

But no studies have demonstrated a similar effect with the coronavirus vaccine, and the CDC advises people to wait until they are fully recovered before getting vaccinated. This is because the immune system could produce an “overly robust” response for people recovering from infection, Creech said.

There’s no clear cut guidance for people infected between shots, who are usually advised to consult their doctor.

Zach, a 30-year-old Philadelphia entrepreneur, lucked out when a friend told him a mass vaccination site had leftover doses at the end of an early March evening. He wasn’t particularly worried about the virus as a young adult without high-risk medical conditions.

That weekend, he went to a restaurant to dine indoors for the first time in months and joined a small home dinner party with friends. He woke in the middle of the night with a fever a few days later. Tests confirmed he and a friend at the dinner party contracted the virus.

“It’s not like I was running around licking door handles or making out with random strangers, but I was thinking now I can eat indoors even though I knew I hadn’t changed my risk profile that much at that point,” said Zach, who asked his last name not be published to avoid harassment.

His case was mild and he has since become fully vaccinated. Now he’s trying to help others avoid his situation.

“If I hear someone who says I got first vaccine, I say, ‘Hey, just keep in mind you still got to behave safely and keep masking up,” he said. “The first vaccine is not going to totally protect you.”

Others who tested positive for coronavirus after their first vaccine dose have been trying to make sure their bad timing does not fuel vaccine hesitancy among friends and family.

Monica Martinez, a 25-year-old Utah resident, has been kicking herself for flying with her husband to visit relatives in Florida over the holidays. She tested negative five days before her vaccine appointment on Jan. 11, but felt feverish on the day of her appointment. Staff at the site told her she could get her shot anyway, but two days later, she tested positive.

“I didn’t tell everyone I got covid, at least not right away, and would say please get vaccinated — it’s not the vaccine’s fault,” said Martinez, a psychology student. “I didn’t want to add to any sensationalism that ‘She just got vaccinated and she got covid two days later, I wonder what that’s about.’”

The disease hit her hard the first few days akin to a bad flu and leaving her with a high heartbeat. Her husband, who also tested positive, is just starting to recover his sense of taste and smell four months later.

“The theme of this is we are trying to be as careful as we can during a pandemic and the one time we slipped up and went traveling is the time we paid the price,” Martinez said. “We learned our lesson.”