There are subtypes of each. Influenza A and B cause the seasonal flu. The subtypes are named by their hemagglutinin (H) and neuraminidase (N). E.g. H1N1, H5N9, etc.
Turns out the answer can be found here:
https://www.cdc.gov/flu/about/viruses/types.htm
"There are four types of influenza viruses: A, B, C and D. Human influenza A and B viruses cause seasonal epidemics of disease (known as the flu season) almost every winter in the United States. Influenza A viruses are the only influenza viruses known to cause flu pandemics, i.e., global epidemics of flu disease. A pandemic can occur when a new and very different influenza A virus emerges that both infects people and has the ability to spread efficiently between people. Influenza type C infections generally cause mild illness and are not thought to cause human flu epidemics. Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people."
"Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes (H1 through H18 and N1 through N11, respectively). While there are potentially 198 different influenza A subtype combinations, only 131 subtypes have been detected in nature. Current subtypes of influenza A viruses that routinely circulate in people include: A(H1N1) and A(H3N2). Influenza A subtypes can be further broken down into different genetic “clades” and “sub-clades.” See the “Influenza Viruses” graphic below for a visual depiction of these classifications."
So the answer is: 198 possible strains, 131 that actually occur. That explains why they have to pick and choose.
It does raise the question of why they couldn’t just put a bit of all 131 subtypes in the vaccine. Or if that’d overload the immune system, say, the X subtypes most likely to makeup say 99% of probable flu season strains.
We’ve had people even recently refusing to give their kids polio, tetanus, or measles vaccines - and even 5 minutes of honest research or questions to a doctor will make quite clear how bad an idea THAT is. Getting 100+ flu vaccines, all which would have to go through a pipeline taking nearly a decade, when ‘nothing bad has happened’ on that topic for a hundred years?
Ain’t nobody going to pay for that.
We’ll see how the calculus is different soon. I for one would rather my tax dollars go towards figuring something like never having the flu again than blowing up some random middle eastern country a couple more times.
$20 (likely current retail cost of a flu shot) x the 46 million older adults in the US is a hair less than a billion a year. Making 131 or so effective flu vaccines and getting them through the process with the prior known and effective process? (including all the failed attempts)
Hopefully we’d get some economies of scale, estimates [https://www.passporthealthusa.com/2018/02/how-much-does-it-c...] I found had it between 500m to 2.5billion and a decade each. So 65billion to 327billion.
So between 65 to 327 years for positive ROI if that was your metric.
If you’re talking public good, it would be immeasurable for us and the world though, no question, and on the high end that’s less than a third [https://www.google.com/amp/s/www.bbc.co.uk/news/world-473918...] of what we’ve spent in Afghanistan alone.
We'd need try to find out, which I personally think would be way better for everyone involved than many other things we spend money on. So take that as my vote for trying?
It's not that hard to make a new vaccine, the process for flu is very accelerated because they're just a variation on the original theme which has been proven to be safe (though unclear on effective until AFTER the flu season hits). If you think about it, we make a new flu vaccine every year, and develop it in 6 months. Each one contains a few guesses as to which of the flus are going to be an issue, it's not just one antigen in the vaccine. Those guesses are just that, an informed prediction, which is why the vaccines tend to be fairly ineffective (40-60%) at preventing disease altogether, though perhaps better at preventing serious disease.
Moderna is claiming to be quicker, so they'd have a more accurate read on what the REAL flu strain this year is going to be, and so it should be more efficacious. The key variable will be dosing. mRNA vaccines can only deliver a certain amount of mRNA so it might be impractical to deliver very many antigens at once. Also delivery issues, the current flu vaccine is super easy to make and deliver to patients, mRNA vaccines with their complicated cold chains aren't. Obviously it's not an impossible problem, but it's less convenient.
Time will tell, it's certainly very promising!
Helpful: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3619640/
https://www.who.int/influenza/vaccines/virus/recommendations...