View report page

poliomyelitis have been shown as they occurred in the same month and in the first,
second and third months following inoculation, i.e., a total period of four months.
Therefore, in construction of the ' exposed to risk ' for the ' not inoculated ' group,
children given a final inoculation in the same month and in the preceding three months
should be excluded and this has been done in the Table. The number of children inoculated
was derived from the one in five sample census of the entire inoculated ' population' in
1949. The numbers inoculated in the last three months of 1948 and the first three months
of1950 have been estimated on the basis of the 1949 figures. The former are required in the
calculation of the exposed to risk in January, February and March, 1949, and the latter
for the calculation of the exposed to risk in January, February and March, 1950. From
these figures attack rates have been calculated month by month.
These attack rates have been applied to the numbers at risk in the inoculated groups
to calculate the expected number of cases, shown in italics against the relative observed
number (Tables 1A, IB and 1C). We have, therefore, month by month, the number of
cases observed with the expected number on the basis of the experiences of the ' not
inoculated' children at the particular seasonal level of prevalence of poliomyelitis.
Correction for seasonal fluctuation of risk has thus been fully carried out. The reason for
carrying the calculation of the expected rates into January, February and March, 1950,
is to apply these rates to those inoculated in the months of October, November and
December, 1949, for the first, second and third months of exposure following
inoculation. A comparison of the observed number of cases of poliomyelitis with the
expected number (based on the experience of the children not inoculated) for the
different antigens used month by month is given in Table 3. This is for all intervals
following inoculation aggregated together.