Interrupting the transmission of respiratory tract infections: Theory and practice

Interruption of transmission has always been one of the most attractive app roaches for infection control. The technologies available were severely lim ited before the development of appropriate vaccines. Mathematically, the pr oportion of those who need to be immune to interrupt transmission can be de rived from the Ro, which represents the number of new cases infected by a s ingle case when all contacts are susceptible. Purely respiratory infections have critical characteristics affecting transmission that are different fr om key childhood vaccine-preventable diseases spread by the respiratory rou te. They include frequent reinfections and antigenic changes of the agents. Pragmatic approaches to understanding their potential effect can be found in experimental and programmatic use of vaccines such as those for Haemophi lus influenzae type b and influenza virus infections. Results of these expe riences can in turn strengthen the development of transmission theory.