People previously infected with the virus that causes Covid-19 may need just one dose of a vaccine to gain immunity to the disease, according to a letter from researchers published Wednesday in the New England Journal of Medicine.
Researchers from the Icahn School of Medicine at Mount Sinai in New York City shared the recommendation after studying 109 people with and without prior immunity to the novel coronavirus.
Within days of their first dose of one of the two vaccines currently approbed in the United States, study subjects who had survived a prior Covid-19 infection developed antibodies at a rate 10 to 20 times higher than the uninfected group.
In fact, that faster response was similar to the immune response from a booster shot in people not previously infected, researchers found.
“We showed that the antibody response to the first vaccine dose in people with pre-existing immunity is equal to or even exceeds the response in uninfected people after the second dose,” Dr. Viviana Simon, a microbiology and infectious disease professor, said in remarks separate from the letter she co-authored.
“For that reason,” Simon continued, “we believe that a single dose of vaccine is sufficient for people who have already been infected by SARS-CoV-2 to reach immunity.”
Using just one dose where possible can stretch a short vaccine supply, and spare some from experiencing unpleasant vaccination side effects, like fatigue and fever, which the researchers say are significantly greater in those who already have some immunity to the coronavirus causing the pandemic.
Side effects, which remain relatively mild for all three vaccines, are more common after the second dose of vaccine.
To examine systemic side effects — meaning those that affect the whole body, rather than an isolated part — Simon and colleagues tested a second group of 231 study subjects, 83 of whom had tested positive for Covid-19, and 148 who hadn’t.
The researchers observed symptoms like pain, swelling and skin reddening in both groups. The group with some immunity, though, experienced side effects more frequently, and those included fatigue, headache, chills, fever, and muscle and joint pain.
In people already infected with the coronavirus, the remnants of an immune response prime the body to react once again. That more vigorous reaction to a perceived threat accounts for the severity of symptoms.
Possibly speaking to the complexity of immune responses, some patients who recovered from Covid-19, but had lingering symptoms, have also reported feeling better after getting vaccinated.
In an interview last week, Kim Litwack, professor and dean of the University of Wisconsin-Milwaukee’s College of Nursing, noted that data is not yet available to determine if this is a widespread trend.
One theory, she explained, points to “lingering fragments of virus that remain in the body after infection, which continue to irritate the immune system.”
“After vaccination, the body responds by building more antibodies, which may finally rid the body of these viral fragments,” Litwack said, noting that more research is needed to confirm that theory.
With the new findings signaling the potential for a change in vaccine distribution policy, questions arise about what to do if a vaccine-eligible person isn’t sure whether they previously had Covid-19.
Researchers suggest using a serologic test to scan for antibodies.
“If the screening process determines the presence of antibodies due to previous infection, then a second shot of the coronavirus vaccine may not be necessary for the individual,” Simon said.
“And if that approach were to translate into public health policy, it could not only expand limited vaccine supplies, but control the more frequent and pronounced reactions to those vaccines experienced by Covid-19 survivors.”