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Herd immunity

My social media platforms are stuck in an anti-vaxx algorithm and I'm being shown tons of ragebait anti-vaxx posts. I know I need to stop interacting with the posts in order for the algorithm(s) to free me of this hell, but I haven't been able to yet -- they just keep sucking me in.

Anyway, I keep seeing comments about herd immunity:

herd immunity isn't a thing. Or was it just not a covid thing???

This is a comment from someone on a social media post about the measles outbreaks we are experiencing. So here's my response to this kind of commentary, because it seems people are either really confused and just don't really know how this stuff works, or they are blissfully ignorant and just parrot talking points or other social media influencers.

Herd immunity requires all three of these to be true: that the virus is spread by human to human contact, does not rapidly mutate, and we have sterilizing immunity (vaccines).

Flu, COVID, norovirus etc. do not have the capability for herd immunity because it only takes just one of those three things to not be true for a pathogen for herd immunity to not work. In this case, rapid mutation is the main issue. The vaccines we make for the flu are usually about ~40% effective at sterilization immunity (preventing influenza) because the flu virus mutates; this is the same case for COVID. The COVID vaccines were not sterilizing vaccines, meaning they were not to prevent being infected by COVID, but are used to decrease the serious complications from the virus -- and additionally, COVID mutates rapidly.

Measles, polio, diphtheria, smallpox are some examples where herd immunity can exist. We have created sterilizing immunity vaccines to prevent infection and these pathogens have been consistently the same for decades and they are transmitted by human to human contact.

Stuff like tetanus we can vaccinate for personal protection but even if 100% of people have the tetanus vaccination, we can still get it as it isn't transmitted person to person, but it is environmental only; so this means that herd immunity doesn't work on pathogens like that or animal vectors like rabies or malaria.

I don't know if you'll actually read this and think about it, and if you don't, that's fine. Someone else might find it useful.

o D E r ( o n e e h v A . s u i n g R m r i . a t a o m , b h n n a i e - m l T e t N e e s p o o n V t ) N a - t e a O t h a c n h u l t u H o m o s E g a r , R e n D n t R ( I r r a e M e a p . M l n D m i g U y s o u d . F N m e t , l I s i s a M u T o s t u C ) Y l s t e t O e i Y h Y a V l o e e r e t I y n s a s i D ? v p o , N S V o i i n o t a n r d n e c u l - r c s y i i ? l n N i e o z a D s v t o t a i e c o w r c n e i i l n N h i e o a z ? H v i E e n P s s ( R g a a t e P D a t m o . o h e p g l I o s . i M g & , o M Y e i , U e n v n M N s a f e S I s c e a m T t c c s a Y a i t l l y n i e l P s e o s p O n , o S x S ) I B L E

So when the pathogen meets all the biological critera for herd immunity, we only achieve herd immunity the Herd Immunity Threshhold is met. This thresshold is a specific percentage of the population, and not all pathogens have the same threshhold! The thresshold for each pathogen is determined by how contagious ($R_0$) it is. Here are some examples.

Disease Contagious ($R_0$) Herd Immunity Threshold (HIT)
Measles 12 - 18 93% - 95%
Pertussis (Whooping Cough) 12 - 17 92% - 94%
Diphtheria 6 - 7 85%
Rubella 6 - 7 83% - 85%
Polio 5 - 7 80% - 86%
Smallpox 5 - 7 80% - 85%
Mumps 4 - 7 75% - 86%

Comments or corrections?

#health