Okay, re: any cross-protection from vaccines, the answer is again likely no. For years people have been working on a “universal vaccine” so we wouldn’t have to do annual shots. There is currently work being done with the mRNA technology that came out of COVID, as well as universal HA targets. But we are, for the moment, still stuck with traditional flu vaccines.

Our current flu vaccines work by stimulating the production of antibodies targeting two surface proteins of the flu virus, HA and NA. These control viral attachment/fusion and release, respectively, which are important for viral infection and replication. When we think about vaccine effectiveness studies we want to see those HA and NA titres high because they are linked with protection.

The human vs avian strains of influenza behave differently when it comes to these proteins. HA proteins of human-to-human strains recognize α(2,6)-linked sialic acid, while avian strains use α(2,3)-linked sialic acid. Not every species has tissues with both of these sialic acid receptors. Some do - like pigs, quails, and turkeys - which is where we see viruses start to shift and cause problems for humans. So, mutations in those HA proteins in avian influenza is what decides whether they can reproduce in humans.

In other words - our current swine flu “H1” vaccine is unable to target any avian flu “H1” protein, and that’s actually a good thing! It means that the strains are well and truly separate, and avian influenzas cannot readily reproduce in humans without additional mutation. If and when we start to see human-to-human transmission of H5, then we can look at that strain’s protein structures and determine appropriate targets for vaccination.