In those names of flu, “H” stands for hemagglutinin, and it’s the protein the virus uses to stick to the outside of a cell. “N” is kind of the opposite. It’s the protein neuraminidase that the virus uses to escape from a cell after reproducing. If you think of human cells as having lots of entry and exit doors, each one of which has a different lock, H and N are the keys the virus is carrying to get in and get out.
If two viruses that are are coded H5N1 and H5N3, they’re both carrying the same (or similar) version of hemagglutinin, but they’re carrying quite different versions of neuraminidase. Still, if someone was recently infected by the first virus, they’d have pretty good protection against the second. However, if something like H3N2 rolled up, neither of the defenses the body has cranked up against H5N1 would hold.
Each year, researchers look at the cases of flu they are seeing, with an eye toward those which haven’t been around in awhile, and try to produce a vaccine that hits the most likely varieties. They get especially worried when they see a virus in animals carrying a protein pair that hasn’t run around in humans for decades.
That’s what makes this new vaccine strategy exciting.
Current influenza vaccines, composed of four influenza viral antigens, provide little protection beyond the viral strains targeted by the vaccines. Universal influenza vaccines that can protect against all 20 lineages could help to prevent the next pandemic. Designing and manufacturing a vaccine that can provide such broad protection has been challenging, but the demonstration of the feasibility of mRNA–lipid nanoparticle COVID-19 vaccines offers a possible strategy.
If it seems like that vaccine design includes just about every buzzword for hot new vaccine technologies, you’re right. The mRNA COVID-19 vaccines from BioNTech and Moderna are the fist such to be authorized for use in humans. But now that the door is open, there’s tremendous potential in this technology, including a superior flu vaccine.
The vaccine produced by by the Penn team targets all 18 known versions of hemagglutinin. So even if something like the current flu being passed around among bird species makes the leap to humans tomorrow, we would already have a vaccine that was substantially effective.
This wouldn’t mean an end to annual flu shots, and those shots would continue to focus on the most likely varieties to be seen in a season. However, they could also sharply reduce the chance of serious illness from any flu.
There are still several steps remaining to show that this vaccine is safe and effective for humans. Among other things, there are concerns that getting enough vaccine to generate a response to all 18 versions of “H” may turn out to require too large a dose, leading to unpleasant reactions. (Which is exactly why it’s difficult to make a universal COVID-19 shot that addresses all known variants.)
But since the technologies involved in this vaccine have already been tested against COVID-19, expect this vaccine to move forward without running into worries about the use of mRNA or lipid capsules. It won’t be a part of any vaccine you use this year. But next year? Maybe.