LIVE POLIO IRUS VACCINES

152
Saf ety-Field Evidence of Safety
TABLE 4.
WEEK OF ONSET OF ENTEROVIRUS INFECTION IN MORGAN CITY FAMILIES
Vaccine Household
Virus first excreted in indicoted week
fed number -1 2 3 4 5 6 7 8 9 l0 11
201 Ad P3,B3
205 Pi P3 B3
206 Eio P3
210 p3,Ad PI B3 B2
2 14 B 3 P3 E 19
215 B 3 B 2 E14
Placebo 217 UN B 3
21 8 Ps,B3 B82
219 B2 E14 B3
221 83
222 B2 El14
223 P3,B2 B3
224 Ps B2 Ad2,B5
202 Ps B3
203 PS
204 Ps Pi 82
207 Ps 83
208 P3 B2 B3 UN
Type 3 211 P3 Ad2 Pi B2
virus 212 P3 B2
21:3 Pi P3,B2 B3 El9
216 Ps B2,E
220 P3 Els Ad i
225 Ps UN
226 P3s _ E7 UN
P = poliovirus; E = ECHO virus; B = Coxsackie group B vrius; Ad =
virus; types designated by numerals, e.g. P1 = poliovirus Type 1.
adenovirus; UN = unidentified
DISCUSSION AND SUMMARY
The most infective available vaccine strain of
poliovirus, Sabin's Type 3, was widely introduced
into two small, cohesive communities under conditions
considered optimal for its spread. These
conditions included, in particular, a high proportion
of susceptible young children among an
abundant child population, intense interhousehold
social contact, very poor environmental and
personal hygiene, and heavy seeding of the child
population with large doses of the vaccine virus
to insure maximal pharyngeal excretion at a time
when wild strains normally begin active spread.
Despite these conditions, the results observed
lend further support to the conclusion suggested
by previous observations, including our own
study of intrahousehold spread, that the potential
of the vaccine strains for spread is relatively
limited as compared to that of wild poliovirus
strains. Active spread was observed only in the
first two or three weeks after vaccination, and it
essentially terminated with 51 per cent of the low
and 72 per cent of the high-titer children (62
per cent overall) still untouched. These figures
take into account infections related to the late
recurrence of P3 virus in Franklin which may
have represented the entrance of a wild strain.
The two important implications of this restricted
ability to spread are: (1) that concern as to reversion
of vaccine strains to significant virulence
may be rather academic; and (2) that spread
cannot be relied upon to immunize susceptibles
missed during vaccination programs. This latter
implication is reinforced by the observation that
infections resulting through contact, possibly because
of transmission of a minimal infecting
dose, are frequently abortive and fail to induce
immune response.
The study also provides additional information
regarding factors that may influence virus spread.