Overview
- Published in Nature on March 11, the Weill Cornell–led, multi-institutional study analyzed 40 participants, including children aged 2 to 6 with documented sequential first exposures to H3N2 and H1N1.
- After an initial H3N2 exposure, children generated cross‑reactive antibodies that bound both subtypes yet failed to neutralize most H1N1 strains, and these antibodies could interfere with more potent anti‑H1 responses.
- Cryo‑electron microscopy indicated the loss of activity likely stems from a single amino‑acid difference in the H1N1 hemagglutinin stalk, with particularly poor performance against older H1N1 strains.
- Infants vaccinated simultaneously against H1N1 and H3N2 showed no sign of the deleterious imprinting seen after sequential natural exposures, suggesting concurrent early vaccination may avert this effect.
- The findings highlight immune imprinting as a key factor for vaccine design, while public guidance remains unchanged with the American Academy of Pediatrics recommending seasonal flu vaccination from six months of age.