A study by researchers at the University of Maryland School of Medicine suggests that people who have already had COVID-19 may not need both doses of the vaccine to be protected from the virus.

The emerging research comes as states, including Maryland, face continued vaccine shortages, leaving the growing list of eligible patients to scramble for few available appointments. But experts say that withholding second doses could present logistical obstacles for an already challenged process.

The study, which isn’t yet peer reviewed, evaluated antibody responses to one dose of the Pfizer and Moderna vaccines among health care workers who had previously tested positive for COVID-19 compared with that of health care workers who hadn’t caught the virus. It included people who had experienced coronavirus symptoms during their infection and people who hadn’t.

The researchers’ findings indicated that, in times of vaccine shortage, patients who have had laboratory-confirmed coronavirus infections – whether or not they experienced symptoms – could justifiably only receive a single dose of the vaccines and that those patients “can be placed lower on the vaccination priority list.”

As part of the study, researchers drew blood from the 59 participants on the day they received their vaccine, a week later, 10 days later and 14 days later.

“What we found was that the group that had COVID before had much higher antibody responses than the people who were not infected,” said Dr. Anthony Harris, professor of epidemiology and public health at the University of Maryland School of Medicine, who co-authored the study alongside associate professor Dr. Mohammad Sajadi. “It’s not surprising. That’s what the hypothesis was. But the reason why we think it’s particularly relevant is the shortage of vaccine.”

The study was funded by the Centers for Disease Control and Prevention, Harris said. And it’s continuing. The doctors are following the 59 participants as they get their second doses of the vaccines.

The early data is encouraging, said Gigi Gronvall, senior scholar at the Johns Hopkins Center for Health Security. But verifying prior COVID-19 infections in order to redirect second doses could be just another hurdle for a complicated vaccine rollout process that can’t handle many more, she said.

“Every wrinkle that you put into the logistics may make things a little bit more challenging,” Gronvall said.

For now, people eligible for the vaccine should follow the guidance of health officials and their health providers, she said – especially those who didn’t receive a positive test confirming that they had COVID-19 or only received an antibody test result.

“If you don’t know that you had COVID – if you were weren’t diagnosed with COVID – don’t do self-diagnosis and then decide you don’t need the second shot,” Gronvall said.

Harris emphasized that the University of Maryland study needs to be replicated but that it could be helpful for local and national officials as they try to determine how to distribute the vaccine with limited numbers. He said that while a two-dose regimen would be ideal, many places “don’t have that luxury.”

“The take-home message is basically that if you have a shortage (of vaccine) and if you as a government are trying to decide how to potentially more wisely use a limited number, we think that a single dose of vaccine for people who already have lab-confirmed COVID could be considered,” he said.

A study completed by researchers at Icahn School of Medicine at Mount Sinai in New York tells a similar story. That study found that the antibody response to the first vaccine dose in people who previously had COVID-19 is “equal to or even exceeds” the response after two doses in people who haven’t had the virus.

That study was a bit larger than the University of Maryland’s. It included 109 participants – 41 people who had been infected and 68 who hadn’t.

Withholding the second dose of the vaccine from people who’ve already had COVID-19 could also “spare them from unnecessary pain,” the researchers wrote.

Those with previous coronavirus infections reported side effects like fatigue, headache, chills and fevers at significantly higher frequency than those who had never caught COVID-19, the study said.