LIVE POLIO IRUS VACCINES

472 Efficacy-Field Evidence
TABLE 11.
ESTIMATED PROTECTION BY CHAT-VIRus AGAINST PARALYTIC POLIOMYELITIS IN LEOPOLD-
VILLE AFRICAN CHILDREN 6 MONTHS THROUGH 2 YEARS OF AGE
- ----
DISTRICT
PERIOD*
GROUP
CASES
PERSON-
WEEKS
(p-W)
RATE PER
105 P-w
ESTIMATED
PROTECTION
Ancienne Cité
Nouvelle Cité
Five Districts
Alit
1
1
2
1
2
V
NV
V
NV
V
NV
V
NV
V
NV
V
NV
V
NV
4
27
13
5
2
41
8
18
4
13
5
18
34
85
64,800
205,200
774,800
142,480
47,800
284,200
677,560
295,880
130,400
133,600
686,920
305,240
6.2
13.2
1.7
3.5
4.2
14.4
1.2
6.1
3.0
9.7
0.7
5.9
2.6
7.7
(%)
53
52
71
80
68
88
67
* 1 = Period of Type 1 epidemic, October 1958 through March 1959.
2 = End of April 1959 through April 1960.
t Excluding period 1 in Nouvelle Cité.
rate of 7.7 cases per 100,000 person-weeks in
the unvaccinated population, and 2.6 cases per
100,000 person-weeks in the vaccinated. The
estimated protection from these figures is 67 per
cent. Note that the Ancienne Cité has an estimated
protection of somewhat less.
The second method of calculation (Table 12)
employed the expected number of cases in vaccinated
individuals, determined by multiplying
the number of cases during a given week by the
number vaccinated as of two weeks previously
and dividing that by the total number of susceptible
individuals. It was found that 69.55
cases would have been expected in vaccinated
individuals whereas only 36 actually occurred.
Chi-square was highly significant with a probability
of less than .01.
It may be objected that the evidence of protection
should not be quite so good considering
that most of the recent cases apparently have
been caused by Type 3 virus. In this regard, it
is of interest that in the Ancienne Cité where no
Type 1 viruses were isolated during the Type 3
epidemic, there was poorest evidence of protection,
whereas in the other two areas where some
Type 1 viruses were isolated during June, July,
and August 1959, the apparent protection was
higher. In other words, the areas which showed
TABLE 12. SIGNIFICANCE OF ESTIMATED PROTECTIVE EFFECT OF CHAT VACCINE AGAINST POLIOMYE-
LITIS IN VACCINATED LEOPOLDVILLE AFRICAN CHILDREN 6 MONTHS THROUGH 2 YEARS
DISTRICT
CASES
OBSERVED
CASES
EXPECTED
CHI-
SQUARE
Ancienne Cité 17 23.73 1.91
Nouvelle Cité 10 20.89 5.67
Five Districts 9 24.93 10.28
All 36 69.55 17.86*
*n= 2; p