Since September last year, many countries have been using ‘bivalent’ vaccines against different strains of Covid-19, with the aim of ensuring better protection against possible futures, versus the ‘original’ version of the vaccines. However, several scientific studies have shown that a phenomenon that occurs in our bodies, called immunological imprinting, may make these bivalent vaccines less effective than expected.
Two studies published in January in the scientific publication New England Journal of Medicine (NEJM) indicated that bipolar boosters developed to fight two sub-variants of Omicron and the original strain of Covid-19 did not generate significantly more than antibody responses. Dose escalation for mRNA vaccines.
The scientists suggest that this observed ineffectiveness is related to immune imprinting.
What is it and what does it include?
Immune imprinting is the tendency, when confronted with a new or slightly different version of the same pathogen, either through infection or vaccination, to repeat its immune response based on the first variant encountered.
This phenomenon was first observed in 1947, when scientists “previously had the flu, and then were vaccinated against a circulating strain, developed antibodies to the first strain they encountered.”
For years, scientists have known that after the body is first exposed to a virus, it creates memory B cells, which circulate in the blood and rapidly produce antibodies whenever the same viral variant causes infection.
The problem occurs when a similar but identical variant of the same virus enters the body. In these cases, the immune system, instead of making new B cells, activates memory B cells, which produce “antibodies that can lock in features found in old and new types,” a Nature study cites.
What do new studies say?
The first study, by researchers at Columbia University Vagelos College of Physicians and Surgeons in New York, involved 40 participants who had already received three doses of the original vaccine. 19 were boosted with the original vaccine, while 21 bulls were boosted with the new ‘bivalent’ version of the vaccine.
It found that the ‘bivalent’ vaccines, when compared to boosters made with the original monovalent vaccines, “did not generate a particularly high peak neutralizing antibody response” across all tested Covid-19 strains.
The second study, from Beth Israel Deaconess Medical Center in Boston, USA, compared the results of 15 participants who received boosters with the original vaccine and 18 who received the bivalent vaccine. “Mean neutralizing antibodies to the PA.5 omicron subvariant were similar after boosters with monovalent or bivalent mRNA vaccines, favoring the bivalent dose booster by a factor of 1.3.”
Both groups of scientists attribute this to the effects of immune imprinting.
How to deal with this situation?
Many studies are currently underway to find a way to manipulate the immune imprint. Some scientists argue that nasal or oral vaccines are better at preventing infection than those given by the nose, arguing that the mucous membranes create more protection.
Researchers are trying to find out whether more spaced annual doses of Covid-19 vaccines could help solve the immune imprinting problem.