RF Annual Report - 1935 - The Rockefeller Foundation

INTERNATIONAL HEALTH DIVISION 33
to bring the breeding index down to 2 or 3 per
cent, but latterly it has been found economically
possible to bring it down practically to
zero. In Rio de Janeiro, with a population of over
one and a half million, and with 270,000 houses
containing millions of potential breeding places,
it is now
possible to go for weeks at a time
without discovering a single stegomyia mosquito;
when such a mosquito is discovered, it is along
the waterfront or railway line, indicating the
reintroduction of the species rather than previously
undetected breeding places.
Most of the activities of yellow fever investigation
at the laboratories of The
Rockefeller
Foundation in New York City were concentrated
in 1935 on improving the method of vaccination
in order to make immunization more practical
and more readily available to large populations.
Encouraging results were obtained in the prolonged
cultivation of yellow fever virus in tissue
cultures for the purpose of reducing its virulence
without altering its valuable antigenic properties.
Although the virus grown in tissue cultures
loses much of its initial virulence, and is used at
present for human vaccination in place of the
highly neurotropic mouse passage virus previously
employed, it is still considered unsafe for
use in human vaccination without simultaneous
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