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The tough part about vaccines is that they only protect the recipient from the disease if they get the vaccine, and they only eradicate the virus if everyone on

The tough part about vaccines is that they only protect the recipient from the disease if they get the vaccine, and they only eradicate the virus if everyone on the planet is vaccinated. The Science (making the vaccine) and cost (creating enough vaccine) are only two barriers. Getting everyone (and it really must be EVERYONE) to take the vaccine is a very challenging project. That's what makes the story of [edit: smallpox] so fascinating. Here's a relevant TED Talk about pandemics: http://www.ted.com/talks/larry_brilliant_wants_to_stop_pandemics.html http://www.ted.com/talks/larry_brilliant_wants_to_stop_pande...

rdl 15y ago
You don't need to get 100% vaccination to eliminate the disease; somewhere around 90% works, unless it's incredibly contagious and in a high density environment. "Herd immunity" protects the others -- basically, the disease itself can't spread if a sufficient number of people are vaccinated, so it dies out in a few generations (of the disease, not of humans).
- ComputerGuru 15y ago
  From my classes in veterinary medicine, I believe the herd immunity is around the 80% mark, at least for livestock and their diseases.
  - rdl 15y ago
    It depends on a lot of factors -- how many people will catch the disease, assuming no one is vaccinated, per infected individual is the primary one). I think most livestock diseases are aerosols (foot and mouth disease, etc.), and so are a lot of human diseases, but thankfully not AIDS. The problem is the standard models of herd immunity depend on some simplifying assumptions which may be true in livestock, but are not true in humans -- specifically, that it's a homogenous population with equal chance of giving any other individual the disease, and that vaccines will be distributed fairly randomly as well. If you have backwater villages which never get vaccinated, and are highly interconnected, you can end up with persistent reservoirs of disease, even if it's only 1% of your overall population. Then, you can have periodic epidemics when an individual from that area travels to an unvaccinated area elsewhere (because compliance rates on vaccination go down once the disease is "cured" in a population). (I know about this from drinking with some of the UN/WHO vaccination people in Afghanistan)

rdl 15y ago

You don't need to get 100% vaccination to eliminate the disease; somewhere around 90% works, unless it's incredibly contagious and in a high density environment. "Herd immunity" protects the others -- basically, the disease itself can't spread if a sufficient number of people are vaccinated, so it dies out in a few generations (of the disease, not of humans).

ComputerGuru 15y ago
From my classes in veterinary medicine, I believe the herd immunity is around the 80% mark, at least for livestock and their diseases.
- rdl 15y ago
  It depends on a lot of factors -- how many people will catch the disease, assuming no one is vaccinated, per infected individual is the primary one). I think most livestock diseases are aerosols (foot and mouth disease, etc.), and so are a lot of human diseases, but thankfully not AIDS. The problem is the standard models of herd immunity depend on some simplifying assumptions which may be true in livestock, but are not true in humans -- specifically, that it's a homogenous population with equal chance of giving any other individual the disease, and that vaccines will be distributed fairly randomly as well. If you have backwater villages which never get vaccinated, and are highly interconnected, you can end up with persistent reservoirs of disease, even if it's only 1% of your overall population. Then, you can have periodic epidemics when an individual from that area travels to an unvaccinated area elsewhere (because compliance rates on vaccination go down once the disease is "cured" in a population). (I know about this from drinking with some of the UN/WHO vaccination people in Afghanistan)