Were vaccines relevant to 20th century US mortality improvements?

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I heard a vac­cine skep­tic claim that “90% of the de­cline in in­fec­tious dis­ease mor­tal­ity in the 20th cen­tury in the US was due to fac­tors other than vac­cines.” I won­dered, is that right?

My guess is yes—but at the same time, I think this is very mis­lead­ing. That statis­tic makes it sounds like vac­cines just aren’t very im­por­tant to health—sort of a sideshow in the fight against in­fec­tious dis­ease. But here’s what the stat leaves out, and why vac­cines still mat­ter:

First, the great­est vic­tory of vac­cines was over smal­l­pox. Smal­lpox vac­ci­na­tion was in­vented in 1796, and other im­mu­niza­tion tech­niques were in use in England and Amer­ica as early as 1721, so by 1900, im­mu­niza­tion had already been fight­ing smal­l­pox for well over 100 years. Smal­lpox is also the only dis­ease we have ever com­pletely erad­i­cated—wiped off the face of the earth—and it was only pos­si­ble be­cause of vac­cines. But by the 20th cen­tury, most of what re­mained to be done here was out­side the US. So start­ing the clock in 1900, and re­strict­ing to the US, carves out most of the progress against smal­l­pox.

Se­cond, if we look just at the US in the 20th cen­tury, one of the great­est vic­to­ries of vac­cines was over po­lio. But the dev­as­ta­tion of po­lio wasn’t just death—it was paral­y­sis. Ten to twenty times more peo­ple were par­a­lyzed by po­lio than died from it (es­pe­cially af­ter the “iron lung”). Un­like some other dis­eases, we weren’t able to fight po­lio with bet­ter san­i­ta­tion or hy­giene—in fact, it is be­lieved that im­proved clean­li­ness caused the po­lio epi­demics of the late 1800s and early 1900s. (Ba­si­cally, be­fore good san­i­ta­tion, most peo­ple were ex­posed to po­lio in in­fancy, when they still had lef­tover im­mu­nity from their moth­ers, and when the dis­ease is less likely to cause paral­y­sis. Cleaner wa­ter led to a first ex­po­sure later in life, which led to a much worse dis­ease.) So a vac­cine was re­ally our only weapon.

Third, in gen­eral, phar­ma­ceu­ti­cals have been a bit ahead of vac­cines. For some dis­eases, such as diph­the­ria and tu­ber­cu­lo­sis, an an­ti­toxin or an­tibiotic was available be­fore a vac­cine was. This is also ba­si­cally the story with in­fluenza/​pneu­mo­nia. In­fluenza is a viral dis­ease that of­ten re­sults in an op­por­tunis­tic in­fec­tion of bac­te­rial pneu­mo­nia. The pneu­mo­nia is what kills you. So an­tibiotics for pneu­mo­nia could re­duce mor­tal­ity ul­ti­mately caused by in­fluenza. But just be­cause these dis­eases could be treated with an­tibiotics (or an­ti­tox­ins) doesn’t mean vac­cines weren’t use­ful or valuable. Do you re­ally want to wait to get a dis­ease, and then treat it? Isn’t pre­ven­tion bet­ter than cure? Are you to­tally fine with risk­ing a po­ten­tially fatal in­fec­tion just be­cause drugs ex­ist? What about re­sis­tant strains? And what would hap­pen to an­tibiotic re­sis­tance, if we didn’t have vac­cines and had to treat a much larger num­ber of pa­tients?

Fourth, look­ing only at mor­tal­ity also sim­ply ig­nores a va­ri­ety of less com­mon and/​or less deadly dis­eases that are still im­por­tant, such as chick­en­pox, hep­atitis, mumps, rubella, and tetanus. True, these don’t add up to pneu­mo­nia or TB. But should we then just write them off?

Com­ing back to the origi­nal claim: Good data on these ques­tions is non-triv­ial to come by and to an­a­lyze. But in the US in 1900, the top kil­lers among in­fec­tious dis­eases were pneu­mo­nia, tu­ber­cu­lo­sis, var­i­ous forms of gas­troin­testi­nal in­fec­tions, and (dis­tant fourth) diph­the­ria. The “90% not due to vac­cines” claim is plau­si­ble to me be­cause, for a va­ri­ety of rea­sons, vac­cines may not have been the first thing to dras­ti­cally re­duce mor­tal­ity from these spe­cific causes:

  • Pneu­mo­nia and gas­troen­ter­i­tis can be caused by a wide va­ri­ety of germs (vac­cines only pro­tect against spe­cific germs)

  • Tu­ber­cu­lo­sis, and bac­te­rial forms of pneu­mo­nia and gas­troen­ter­i­tis, can be fought with antibiotics

  • Diph­the­ria had an­ti­tox­ins since the 1890s; the vac­cine wasn’t available un­til the 1920s

  • The tu­ber­cu­lo­sis vac­cine has proved difficult to de­velop; even the best one we have to­day has vary­ing efficacy

  • Similarly, in­fluenza mu­tates so fast that it’s im­pos­si­ble to de­velop and ad­minister a vac­cine for ev­ery strain of it; the an­nual “flu shot” only pro­tects against the strain that we guess will be most preva­lent that year

You could look at all those facts and say that vac­cines are over­rated. And per­haps an­tibiotics de­serve the high­est hon­ors in the fight against in­fec­tious dis­ease. But it would be a mis­take to dis­count or dis­miss vac­cines, for the fol­low­ing rea­sons:

  1. They are our only highly effec­tive weapon against highly con­ta­gious viral dis­eases, such as po­lio, in­fluenza, measles, and (in the past) smal­l­pox.

  2. They com­ple­ment phar­ma­ceu­ti­cals, pro­vid­ing defense in depth. Vac­cines are pre­ven­tion; drugs are cure. You want both.

  3. Drug re­sis­tance is real and pre­sents a risk; and the more we have to use drugs the worse it will get.

  4. Suffer­ing from a dis­ease but not dy­ing from it is still suffer­ing.

The vac­cines the CDC recom­mends for rou­tine im­mu­niza­tion do not in­clude dis­eases that have been suc­cess­fully re­duced by san­i­ta­tion or pest con­trol, such as yel­low fever, ty­phoid fever, and cholera; or by erad­i­ca­tion (smal­l­pox); or those that are oth­er­wise rare (an­thrax). They ba­si­cally only recom­mend vac­cines that are highly effec­tive or are for highly con­ta­gious dis­eases; in most cases both. The flu shot, which is only par­tially effec­tive, and tetanus, which is not highly con­ta­gious, are both com­mon enough in the US to be war­ranted.

Bot­tom line: the 90% claim is prob­a­bly true, but:

  • Vac­cines are still very im­por­tant and de­serve ma­jor credit in the fight against in­fec­tious disease

  • You should still get your shots (and vac­ci­nate your kids).

I’m work­ing on a bet­ter quan­ti­ta­tive anal­y­sis to an­swer: which dis­eases were the worst, and which meth­ods to fight them de­serve most credit? I’ll post here when I have more info. In the mean­time, if you have any poin­t­ers to good pa­pers or data sources on this, let me know.