smallpox vaccine and vaccination in the intensified ... - libdoc.who.int

Vaccine, 1959; see Chapter 7) was recom-
mended and a practical method for preparing
them was described. Slonim et al. (1969)
showed that the viral concentration in the
harvested pulp was 3 times higher when
vaccinifers were scarified with an inoculum
containing 108.3 pock-forming units per m1
than with one containing 107 pock-forming
units per ml. To provide a safety margin, the
document stipulated that the titre of the seed
lot should not be less than 108.7 pock-forming
units per ml. This was substantially higher
than the acceptable titre for vaccination, but
was essential if adequate yields of high-titre
vaccine were to be obtained.
Preparation of vaccintfer
A rigorous schedule for cleansing the
animal skin was recommended, which sub-
stantially reduced the bacterial count to the
extent that very few or no viable bacteria (and
no pathogens) were found in the aliquot of
vaccine (usually 1 ml) cultured.
The recommended method of scarification
was based on the experience of the partici-
pating producers, and an instrument for scari-
fication of the vaccinifer in use in Wyeth
Laboratories was produced by WHO and
distributed to producers on request (Plate
1 1.5).
Preparation of vaccine
The method of extraction and treatment of
the viral suspension was described with special
reference to the specification of the
required potency at each stage of the production.
Phenol was added to a concentration of
0.5% by weight, following observations by
Hekker & van Ramshorst (1969), who had
investigated the phenol content and bacterial
counts of 51 lots of freeze-dried vaccine from
23 laboratories in several countries and shown
that this was the maximum concentration
that would reduce the bacterial count without
affecting initial potency or heat stability.
Before being dispensed into ampoules, the
viral suspension was required to have a titre of
at least 108.7 pock-forming units per ml, since
11. VACCINATION IN THE INTENSIFIED PROGRAMME 553
than 10' pock-forming units per ml, in line
with the standards established by WHO in
1965.
Size of container used for vaccine distribution
The volume of fluid to be dispensed into
each final container was specified as between
0.1 5 m1 and 0.25 ml, which would provide 15-
25 doses per ampoule by the conventional
scarification or multiple pressure techniques
and 60-100 doses for vaccination with the
bifurcated needle. Although ampoules pro-
viding fewer doses were requested by field
workers, production experts agreed that 0.1 5-
m1 lots were the smallest practicable volumes
that could be dispensed and dried.
Reconstituting jttid
Traditionally, glycerol had been used at a
concentration of 40-60°/, in the suspending
fluid of liquid vaccines. It had to be omitted
from the fluid used to suspend the lymph for
freeze-drying, but its properties made it
useful for the reconstituted vaccine. Studies
by Slonim & Roslerovi (1969) showed that, at
the processes of freeze-drying and incubation Plate 1 1.6. Dimitrij Slonim (b. 1925), of the Instiat
37 oc for 4 weeks would somewhat reduce
tute of Sera and Vaccines. Prague, Czechoslovakia.
contributed to methods for the accurate assay of
its potency. The vaccine, after incuba- vaccine and was a member of the Seminar on Vaccine
tion, was required to have a titre of not less Production