I think the "Gilead" missionary school also had an impact on the doctrine in its early stages. Travel abroad, especially to tropical countries has always involved a list of vaccinations as long as your arm. They're not optional and many of them provide immediate passive immunity. (i.e. They contain appreciable amounts of gamma globulin)
They were faced with a choice: Either vaccinations of all types had to be allowed or missionaries would be excluded from many locations.