I am in my forties and have gotten a flu vaccine almost every year since they began to be widely available. If I went back in time would I likely be inoculated against the Spanish Flu pandemic? Or was that strain long gone by the time our inoculations were formulated?
Blame this zombie for the question: http://boards.straightdope.com/sdmb/showthread.php?p=16690160#post16690160
IANAD, but this is my understanding of it.
The flu virus mutates enough that current vaccinations are only good for a few years. The reason you need a flu shot every year is that each shot doesn’t include all strains, it only includes the strains that are going around that year.
The 1918 pandemic was caused by H1N1, a type of influenza A. While you’ve likely received several immunizations over the years for strains from this family, so much time has passed that the strains have mutated to the point where they don’t look at all similar to the 1918 version to your immune system.
Basically, that strain, as it existed in 1918, is long gone. But the strain itself lives on, most recently causing a pandemic scare in 2009.
Maybe.
What happened in the 2009 H1N1 pandemic was informative. As pointed out above that strain shared many commonalities with the 1918 one. One interesting thing was observed in 2009 - those who were born before 1950 tended to get it less often and to have less severe diseaseand young adults had much worse … not the usual circumstance with influenza. The reason?
Now would the same hold in reverse? Probably if you actually caught the 2009 H1N1 and possibly if you were vaccinated with the live weakened nasal vaccine. Also possibly if you’ve kept getting annual injected vaccines as the formulations have (I am fairly certain) continued to include the H1N1 pandemic strain in the mix, which again, likely has plenty of cross coverage with it.
IIRC, our immune system isn’t just sensitive to hemagglutanin and neuraminidase but also to core proteins - which seems counter-intuitive since you wouldn’t think those would be detectable, but it seems that on some level they are. So people who have fought off a particular flu variant do actually have a higher level of immunity - at least from what I recall. When you’re inoculated, you only develop immunity to the H and N surface proteins against which the vaccine was developed.
“Immunization with (…) 2009 pandemic H1N1-inactivated vaccines protects mice from a lethal 1918 influenza infection,” and the authors think that their “data suggest that the general population may be protected from a future 1918-like pandemic because of prior infection or immunization with 1976 swH1N1 or 2009 pH1N1.”
Sorry, missed the edit window. That protection “from a future 1918-like pandemic” should be interpreted very narrowly, of course. From the paper: “Similarly, exposure to the 2009 pH1N1 and the associated vaccination campaign also may contribute to protection against an accidental release or zoonotic re-introduction of 1918 or 1918-like influenza.” For less closely related, potentially pandemic strains, cross-protection is increasingly unlikely.
Also from that citation:
The problem with even killed virus vaccines is that since the virus never gets the chance to replicate in the body, your immune system is never exposed to the internal viral machinery so all it sees in essence is a black box of H and N proteins. That’s why attenuated virus tend to be better for vaccines than killed when that can be managed.