Editor’s note: This article has been updated to remove a paragraph referring to a separate study conducted by the authors of the Qatar study.
A COVID-19 booster, particularly a third dose of vaccine, may reduce protection against re-infection with the omicron variant for some people — and there’s a reason for that, according to new findings.
In contrast, two doses of vaccine, followed by an initial infection with omicron, may protect more against a second infection with omicron than an additional vaccine, according to a preprint study published November 1 on medRxiv, a server operated by Yale, BMJ and Cold Spring Harbor Laboratory. This is due to a specific reaction within the immune system, the researchers concluded.
Here’s what the results mean.
“If you have been infected with Omicron at any time, a third dose of vaccine doubles that as your risk of reinfection vs just 2 doses,” wrote Dr. Daniele Focosi, a specialist in hematology and working at the University Hospital of Pisa in Italy, on Twitter in response to the results. “Incredible immune impression at work.”
The study states that immune fingerprinting is why “three-dose vaccination was associated with reduced protection compared to that of two-dose vaccination.”
But what exactly is the immune fingerprint?
Fortune explains it as “a phenomenon in which initial exposure to a virus – say, the original strain of COVID, through infection or vaccination – limits a person’s future immune response against new variants.”
The authors of the Qatar study wrote how they sought to investigate the “phenomenon” by analyzing COVID-19 data recorded in the country’s national databases at the start of the omicron wave from December 19 to September 15.
The study found that when looking at participants who had received three doses of vaccine and who had also been previously infected with an omicron subvariant, they experienced more reinfections than participants who had only received two. doses.
“This finding suggests that the immune response against primary omicron infection was compromised by differential immune imprinting in those who received a third booster dose, consistent with new laboratory science data,” the authors wrote. .
The researchers note that none of the participants’ reinfections were severe, which was “not unexpected given the lower severity of omicron infections.”
An earlier study that looked at the immune fingerprinting and updating of COVID-19 vaccines hypothesized that “repeated updating” of injections “may not be fully effective” due to the limitations that the immune fingerprint may present. The work was published in November 2021 in the journal Trends in Immunology and appears in the National Library of Medicine online.
The Qatar national study stressed that their results “do not compromise” the benefits that booster doses provide to the public, but the researchers concluded that these benefits may be short-term.
“There is no doubt that the booster dose reduced the incidence of infection immediately after its administration… Nevertheless, the results indicate that the short-term effects of boosters may differ from their long-term effects,” wrote the authors.
The study acknowledges some limitations, including how they looked at recorded reinfections and how some infections could have occurred without being recorded.
The preprint study comes two months after the Food and Drug Administration cleared new booster doses, called bivalent boosters, made by Pfizer and Moderna that target the omicron BA.4 and BA.5 subvariants.
Learn more about immune fingerprinting
Regarding immune fingerprinting, Medical News Today reports that “the ways our immune systems may have been exposed to SARS-CoV-2 markers are myriad,” noting how people received different vaccine formulations and were infected with different COVID-19 subvariants.
“All of these things push and pull your immune repertoire, your antibodies and everything in different directions, and make you react differently to the next vaccine that comes along. […] So this is called the immune fingerprint,” Professor Danny Altmann of Imperial College London, who specializes in immunology, told the media.
Because of this, how one person may react to exposure to the virus can “vary significantly” from the next person, according to Medical News Today.
Fortune points to two recently published studies citing “‘immune fingerprinting’ as a potential reason” as to why new COVID-19 boosters targeting omicron may be unable to “outclass the original vaccine”. One was for Columbia University and the University of Michigan, and another was for Harvard University.
The Harvard-affiliated preprint study published Oct. 25 on bioRxiv concluded that “immune fingerprinting…may pose a greater challenge than currently appreciated for inducing robust immunity against SARS-CoV-2 variants.”
As of November 3, more than 22 million people in the United States, or about 7% of the total population, had received the last bivalent booster dose of COVID-19, according to the Centers for Disease Control and Prevention. Meanwhile, nearly 227 million people have completed their primary series of one or two doses.
The CDC recommends everyone stay up to date on their COVID-19 vaccines.
This story was originally published November 3, 2022 12:18 p.m.