Abstract:
A Rift Valley fever (RVF) epidemic affecting animals
on domestic livestock farms was reported in South Africa
during January–August 2010. The first cases occurred after
heavy rainfall, and the virus subsequently spread countrywide.
To determine the possible effect of environmental
conditions and vaccination on RVF virus transmissibility,
we estimated the effective reproduction number (Re) for
the virus over the course of the epidemic by extending the
Wallinga and Teunis algorithm with spatial information. Re
reached its highest value in mid-February and fell below
unity around mid-March, when vaccination coverage was
7.5%–45.7% and vector-suitable environmental conditions
were maintained. The epidemic fade-out likely resulted first
from the immunization of animals following natural infection
or vaccination. The decline in vector-suitable environmental
conditions from April onwards and further vaccination
helped maintain Re below unity. Increased availability of
vaccine use data would enable evaluation of the effect of
RVF vaccination campaigns.