Factors enhancing resistance may have the highest translational impact. The smallpox vaccine is an example. It was developed before the main risk factor, the variola virus, was discovered, and vaccine production does not even involve this virus. The immune milkmaids, inoculated with cowpox, were the high-resistance population in the discovery of the smallpox vaccine. This example shows that resistance factors are not merely opposite to risk factors, and that extending the action of a resistance factor to the rest of the population may be more practicable than the removal of a risk factor. The most effective measures for HIV/AIDS prevention – condom use and abstention from risky sex or, for injection drug users, from needle-sharing – are also not specific to HIV but increase resistance to infection. Dealing directly with the “pathogen” is appropriate in some cases (e.g., antiretroviral therapy for HIV; antibiotics for bacteria). Such an approach may be infeasible or ineffective in many other cases, while raising resistance to the pathogen may be more promising.
