06.13.2022 | STAT News First Opinion
By Steve Brozak and Richard Marfuggi
This week, when the CDC’s vaccine advisory committee considers approving the Moderna and Pfizer/BioNTech mRNA Covid-19 vaccines for infants and toddlers, the issue of imprinting may not be on the agenda. But it should be, given lessons from the Russian pandemic of 1889, the Spanish flu pandemic of 1918, the Hong Kong flu of 1968, the swine flu pandemic of 1957, and the 2009 H1N1 pandemic.
Immune imprinting results from exposure to proteins or other biological structures of viruses, like those found in SARS-CoV-2, that allow the virus to penetrate host cells and cause infection. The process, also called original antigenic sin, refers to the preference of the immune system to recall existing memory cells (lymphocytes that “remember” the same pathogen for faster future antibody production) rather than stimulating de novo responses when encountering a novel but closely related antigen.
Imprinting may come directly from an acute infection or indirectly through vaccination. It can result in reduced — or enhanced — responses to future variants with unknown clinical consequences. The former is beneficial, the latter is not.
The immune systems of infants and toddlers — the targets of the latest Covid-19 vaccination approval — are immature and developing. If an immature immune system is immunologically imprinted, either by acute infection from the currently circulating viral variant or by a Covid-19 vaccine based on the original, wild-type variant that is no longer in circulation, it may fail to develop appropriate defenses when confronted — even years later — by a Covid variant or another totally different pathogen.
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