Dr. Daniel Berman
NY Daily News
.... However, the New York State Health Department reports the average vaccination rate for measles among the nearly 200 Jewish K-12 schools in Brooklyn — mainly in Borough Park and Williamsburg — is 96%, six percentage points higher than the statewide average among private schools. In contrast, six other New York counties have a vaccination rate below 50%.
Moreover, the measles vaccination rate among Jewish school-age children is above the assumed 95% threshold required for “herd immunity,” i.e., protection of the community from sustained outbreaks.
What, then, explains the outbreak?
Regardless of the vaccination rate, some communities have characteristics that enhance and sustain epidemics. Population density and a community’s social mixing patterns are two critical determinants of whether an outbreak dies out or remains sustained. Orthodox Jewish communities are densely populated. Families have many children and interact frequently.
The vaccination rate of 95%, assumed to provide herd immunity, is derived from a basic model assuming the vaccine is effective 97% of the time, and that, in the absence of immunity an average infected individual transmits the infection to 12 others, the “basic reproduction number” (what we in medicine refer to as “R0”).
If, however, in a densely populated and highly interactive community, the average infected individual transmits measles to 24 others, then 99% of the community must be vaccinated in order to ensure herd immunity. If the average is 36, then even a 100% vaccination rate fails to ensure herd immunity. R0 estimates in the literature vary from 1 to 203.
