Studies find ‘immune imprinting’ might be making bivalent boosters less effective.

• Since last September, countries like the UK and the US have rolled out variant-specific or bivalent boosters, in the hope that they would provide better protection against the coronavirus infection in comparison to the original vaccine.
• However, a slew of recent studies have shown that a phenomenon in our bodies, called immune imprinting, might be making these new boosters far less effective than expected.
• The observed ineffectiveness of the bivalent or variant-specific boosters might be due to immune imprinting, scientists of both studies concluded.

What is immune imprinting?

• Immune imprinting is a tendency of the body to repeat its immune response based on the first variant it encountered — through infection or vaccination — when it comes across a newer or slightly different variant of the same pathogen.
• The phenomenon was first observed in 1947, when scientists noted that “people who had previously had flu, and were then vaccinated against the current circulating strain, produced antibodies against the first strain they had encountered”, according to a report published in the journal Nature.
• At the time, it was termed the ‘original antigenic sin’ but today, it’s commonly known as imprinting.
• Imprinting acts as a database for the immune system, helping it put up a better response to repeat infections. After our body is exposed to a virus for the first time, it produces memory B cells that circulate in the bloodstream and quickly produce antibodies whenever the same strain of the virus infects again.

The problem

• The problem occurs when a similar, not identical, variant of the virus is encountered by the body. In such cases, the immune system, rather than generating new B cells, activates memory B cells, which in turn produce “antibodies that bind to features found in both the old and new strains, known as cross-reactive antibodies”.
• Although these cross-reactive antibodies do offer some protection against the new strain, they aren’t as effective as the ones produced by the B cells when the body first came across the original virus.
• The recent findings of two studies suggested immune imprinting might be posing a hurdle in the success of the bivalent or variant-specific vaccines.