THE EFFECT OF COMMUNITY STRUCTURE ON THE IMMUNITY COVERAGE REQUIRED TO PREVENT EPIDEMICS

Estimation of the immunity coverage required to effectively control di sease transmission is an important public health problem. Using data o n the eventual size of a major epidemic, we compare estimates based on the simplifying assumption that the community consists of uniformly m ixing individuals with estimates obtained when the more complex commun ity structure is acknowledged. The alternative community structures co nsidered include households and localities that are quite separate. Se veral inequalities are established for estimates of the critical immun ity coverage. For several settings, the coverage estimated by assuming an oversimplified community structure is found to actually be an unde restimate. A serious consequence of this finding is that we may be mis led into believing that we have estimated an immunity coverage that ca n prevent epidemics when it in fact cannot. The conclusion is that the heterogeneity in the community must be taken into account when estima ting the critical immunity coverage. (C) 1998 Elsevier Science Inc.