Immune imprinting

What do these studies say?

• Recently studies pointed out that bivalent boosters made to counter both the Omicron strains and the original Covid-19 strain — don’t generate significantly greater antibody responses than an additional dose of the original mRNA vaccines.
• 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. 
• At the time, it was termed the ‘original antigenic sin’ but today, it’s commonly known as imprinting.
• Over the years, scientists have realised that 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 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.

How to circumvent immune imprinting?

• Currently, several ongoing studies are trying to find a way to deal with imprinting. 
• Some scientists have said nasal vaccines might be better at preventing infections than injected ones. 
• They believe the mucous membranes would create stronger protection, despite carrying some imprint of past exposure.
• Researchers are also trying to find if spacing out coronavirus vaccine shots on an annual basis, could help with the problem of imprinting.
• There’s also considerable effort directed toward developing what’s called pan-sarbecovirus vaccines that will protect against all COVID-causing variants and maybe even protect against other SARS and related viruses.