Don Seiffert and Laura Justice of Salem recently returned from a trip to Ireland to discover they had caught COVID-19 — again.
After the couple contracted COVID in May, they figured they’d be protected from the virus on vacation in July and traveled without masks into crowded castles and packed pubs.
“We felt pretty safe,” said Justice, 52. “We were wrong.”
The symptoms started soon after they arrived back home, and were worse than they had been the first time around. Seiffert, 52, an editor at the Boston Business Journal, felt so sick he couldn’t leave his bed. Justice was congested and exhausted, and her head hurt.
“This is not normal,” she said to Seiffert. A test then confirmed the couple’s fears.
For Justice, the result was a shock. “Oh my god, not again,” she thought.
Experts, however, aren’t surprised by stories like theirs — at least not anymore.
“Reinfections were uncommon with the initial strain from Wuhan, with Alpha, with Delta,” said Dr. Jacob Lemieux, an infectious diseases doctor at Massachusetts General Hospital. “They did occur, but they were rare.”
Then, in December 2021, Omicron started to spread across the United States and changed the course of the pandemic. Today, subvariants of the strain, BA.4 and BA.5, account for the majority of new cases of COVID-19 in the United States.
Omicron is “antigenically very distinct,” said Lemieux — meaning the structures on the virus’s surface are different from those of previous variants, making them harder for the immune system to recognize. Subvariants like BA.4 and BA.5 have also been “distinguished by a progressive ability to escape the immune system,” he said.
The United States hasn’t systematically tracked reinfections. But data from countries that have reveal the impact of Omicron. In July 2021, reinfections accounted for less than 2 percent of cases in the United Kingdom, according to its data. By June 2022, reinfections made up over 25 percent of the country’s cases each day.
Time also influences the odds of reinfection, said Dr. Philip Landrigan, an epidemiologist and the director of the Global Public Health Program at Boston College.
“When a person gets infected, or when they get vaccinated, they develop antibodies, and the antibodies are in their bloodstream, and they kill the viruses,” he explained. “Unfortunately, over time — over 4 to 6 to 12 months after immunization or after infection — the antibody levels decline. People’s immunity fades. That’s when the risk for reinfection goes up.”
It’s difficult to say the specific amount of time that takes. According to Landrigan, “there’s no hard and fast number” — though typically the longer it’s been since an individual was infected, the greater the risk of reinfection.
For part of the pandemic, experts thought infected individuals had immunity for at least 90 days, said Dr. David Hamer, an infectious diseases doctor at Boston Medical Center.
But that thinking “has passed. It’s water under the bridge,” he said, citing recent reports of reinfections that occurred as soon as a month after a case of COVID.
“Everybody is basically at risk of becoming reinfected if they had COVID more than 8 or 12 weeks ago, and should be mindful of that,” said Dr. Daniel Kuritzkes, head of the Division of Infectious Diseases at Brigham and Women’s Hospital.
Kuritzkes said the recent rise in reinfections is “not too surprising.”
“We know that immunity against coronaviruses is short lived,” he explained. “Even before COVID-19, people would get colds every year — a quarter of those colds were due to coronaviruses.”
Though there are few formal studies on the subject, experts expect COVID-19 reinfections to be milder than initial bouts with the virus.
“When there’s immunity, either from vaccination or prior infection, the subsequent infections tend to be milder and progress less frequently to severe illness or death,” explained Lemieux. Still, he said, “that doesn’t mean mild.”
Milder but not mild was the case for Lawrence Street, 52, of New Jersey, who contracted COVID-19 in December 2020 before he could be vaccinated. His sickness was so severe he could barely breathe, and he had to receive steroids at a city clinic.
“It felt like there was sand in my chest,” he said. “It was a hot burning feeling — like I was weighted down.”
Street caught another case of COVID-19, in June 2022, after he had been vaccinated and boosted. Though he had prepared himself for the possibility of reinfection, he expected to be asymptomatic.
Instead, Street said, he felt like he had “a mid-grade flu” — fatigue, fever, and chills.
“It was just a bad three days,” he said. Still, Street was sick enough that he felt like he would have been “very, very, very sick” if he hadn’t been vaccinated and boosted.
Experts emphasize that vaccination is vital to protect against severe sickness and death from COVID-19. Studies have also found that individuals who are unvaccinated have a higher chance of reinfection.
“If they’ve been vaccinated, and they’ve had one infection, that should greatly reduce their chances of having complications,” said Hamer.
Each infection also carries a risk of long COVID — a set of sometimes severe symptoms that last long after infection. Currently, there isn’t enough information for doctors to determine how the likelihood of long COVID changes with reinfections.
“We just don’t really know as much as we would like to know about reinfection syndrome,” said Lemieux.
There’s also always a risk of other complications from COVID-19 — a risk that accumulates with each exposure. That was the conclusion of scientists at the University of Washington, who released a preprint of a study last month suggesting reinfections increase the odds of severe sickness, hospitalization, and death.
The study — based on the records of over 5.6 million patients in the Veterans Affairs Health System — found individuals who had contracted COVID more than once displayed double the risk of death and triple the risk of hospitalization in the months after infection as individuals infected only once.
“Anytime you’re in a situation where you’re repeatedly presented with risk — like you’re infected with COVID-19 — than the overall probability of not having a complication will go down over time,” said Lemieux, who was not involved with the study.
The patients in the study who were reinfected also tended to be older and sicker compared to those infected only once, which raised their chance of complications.
Experts expect the rate of reinfections to continue to climb, both because of Omicron and because the majority of the country has already contracted COVID-19 at least once.
“It’s just simple mathematics that more of the infections going forward are going to be reinfections,” said Landrigan.
Nonetheless, he encourages individuals to continue to be cautious about COVID and to wear a mask while in crowds. Landrigan and Kuritzkes also advised using masks on transportation, like airplanes and the MBTA.
“Nobody wants to get infected a second time or third time,” said Landrigan. “Take reasonable precautions. We’ve been dealing with this thing long enough now that we know what works.”
Anyone who is infected — regardless of whether it’s their first, second, or third case of COVID — should speak to a doctor about whether they are eligible for treatments like Paxlovid and monoclonal antibodies, said Kuritzkes.
Such therapies are “highly effective” at preventing severe sickness and death, he said, and “incredibly important” for immunocompromised individuals and patients over 65.
“People definitely shouldn’t feel like, ‘I had COVID and I’m protected.” There’s no forcefield,” said Lemieux. “Infection with SARS-COV-2 is going to be an ongoing risk in the future, and people should make decisions given that risk.”
Camille Caldera was a Globe intern in 2022.Follow her on Twitter @camille_caldera.