LIVE POLIO IRUS VACCINES

Live Virus Vaccine Studies in Southern Africa
479
were immune to Type 1, as they are also immune
after vaccination.
It will be noted that there was a slight change
in immunity status of the Type 2. Some became
immune who were not previously immune. There
was a more marked change with Type 3.
Observations of some interest, and of possible
significance in view of the other findings
reported at this Conference, were that after the
Salk vaccine given in 1958, before the epidemic,
the immunity of 50 children was tested, and of
the 50 only one had antibodies against Type 1,
34 had antibodies against Type 2, and 20 against
Type 3. The immunity given by the Salk-type
vaccine against Type 1 was extremely inadequate.
DISCUSSION
It was apparent from the clinical findings that
the wave of infection had swept through most of
the population of both Mauritius and Rodrigues
by the time the vaccination campaign was begun.
This conclusion was confirmed by the laboratory
studies. Of interest was the high incidence of
positive findings in the pre-vaccination specimens
of feces, 33 per cent. The very high proportion
of the tested children who had antibodies against
Type 1 virus before the administration of the live
virus vaccine, was also significant, indicating that
natural infection spreads very much more rapidly
than the virus vaccine infection. In view of these
findings, no conclusion can be drawn in regard to
the value of the vaccine in bringing the epidemic
to an end. However, it is noteworthy that no ill
effects were reported from either Mauritius or
Rodrigues following vaccination, and in the latter
island, most children who were lacking antibody
developed it to Type 3, and a lesser number to
Type 2 after the administration of the vaccine.
Kenya. In the last decade the epidemiology of
poliomyelitis in Kenya has changed from a
disease of high endemicity with sporadic infantile
cases to one of epidemicity. There has been a
steadily rising number of cases reported each
year from 1945, with two major epidemics, one in
1954 and one in 1957. Both were studied in
detail and it was noted that Europeans, particularly
young children and recent immigrants,
were at great risk, with an attack rate of 244
(1954) and 80 (1957) per 100,000. Asians were
next with attack rates of 40 and 14 per 100,000.
Africans had the lowest rates, of 4.6 and 7.2 per
100,000. In 1957 Koprowski's attenuated Type 1
strain was offered for trial, but after consideration
was not used.
In 1959 a slight increase in the number of
poliomyelitis cases was noted in Mombasa. This
was followed by a sudden occurrence of cases in
the Kerugoya and Embu districts of Central
Kenya, which had been relatively severely affected
in 1957. Nearly all cases were in the
under three year olds. Type 1 poliovirus was
proved to be responsible.
It was decided to undertake a mass immunization
campaign with the attenuated Type 1 poliovirus.
After consultation with Dr. Winter, 60,000 children
were given Sabin's Type 1 strain during
the week ending 12 December. During the seven
weeks preceding this, there had been 25 cases.
In the subsequent seven weeks, there were 16
further cases, five of which were in non-vaccinated
children, and 11 of which occurred within
three weeks of vaccination. Studies since then
have shown that Coxsackie A virus infections
were common among the vaccinated group of
children. This may have had an interference
effect on the infection with the vaccine virus.
The campaign has since been extended and about
1,500,000 children in the Central Province and
in Nairobi have been vaccinated.
The study of the effects is still in progress.
ACKNOWLEDGMENTS
In preparing this paper, I had the help of the
reports of Dr. Loconsci of Mauritius and Dr.
Fendall of Kenya, to both of whom I am grateful.