Physicians who elect to immunize children against smallpox, diphtheria, scarlet fever, pertussis and typhoid fever are confronted by the practical problem of deciding when to administer each prophylactic procedure. A partial solution of this problem probably can be accomplished through the tendency displayed by young infants to be rather refractory to diphtheria and scarlet fever throughout a considerable period during which they are quite susceptible to smallpox and pertussis. This tendency apparently justifies observance of the general policy of temporarily deferring immunizations against diphtheria, scarlet fever and typhoid fever in order that smallpox vaccinations and pertussis inoculations may be completed in the first six months of life.
Whether smallpox vaccinations should usually precede or follow pertussis inoculations is a debatable question. The customary failure of successful smallpox vaccinations when performed during the first three months of life to cause appreciable systemic reactions is a practical point in favor of the