K - College of Natural Resources - University of California, Berkeley

Transmission was predominantly by intimate contacts within households, rather than
via frequent casual contacts among villagers. Limited control measures were imposed
by the villagers, but were judged by the authors of the report to have had little effect on
transmission so we have not divided the dataset.
Smallpox (Variola major), West Pakistan 1968-1970 (Heiner et al. 1971)
This is surveillance data from 47 outbreaks in rural West Pakistan, focusing on
transmission within compounds inhabited by extended families. Of 47 outbreaks, 26
led to secondary transmission, with a total of 70 second-generation cases. Since all
compound residents were in reasonably close contact, generations of cases were
assigned based on the interval between exposure to the index case and onset of illness;
for second generation cases this interval was 9-21 days. The population is reported to
be relatively homogeneous. There was no isolation of contacts from cases, and
vaccination is reported to have “played a minor role”, though it was also observed that
previously-vaccinated index cases tended to be less infectious. Severe illness was
associated with higher infectiousness in this study. A similar study in East Pakistan in
1967 reported 30 smallpox outbreaks, with R~2.2 (stated verbally in the paper) and
p0=13/30, yielding an estimate of k ˆ
pz=0.49
(Thomas et al. 1971).
Smallpox (Variola major), Kuwait 1967 (Arita et al. 1970)
In this outbreak, smallpox was suspected relatively quickly and control
measures were imposed rapidly in the affected hospital. One unrecognized case had
been transferred to another hospital, however, and initiated further spread there before
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