A small-scale feeding trial of an attenuated type 3 poliovirus USOL-D bac vaccine (author's transl)

Abstract

A small-scale trial of an attenuated type 3 poliovirus vaccine prepared with the USOL-D bac strain was carried out as a part of the collaborative study under the WHO's auspices.In two closed institutions 26 children 5 to 13 months of age who had no history of anti-polio vaccination were administered with the vaccine, and 10 children of similar ages were left unvaccinated as room contacts. Of all the children, 21 vaccinees and 5 contacts had no circulating antibody against polioviruses. Most of the children in one institution (Infant Home H) excreted type 2 adenovirus in stools before or during the trial. No viral agent was isolated from pre-trial stools collected in the other institution (Infant Home B).Inoculated with a single dose of the vaccine containing105.8 TCD50 of the virus, the vaccinees in both institutions excreted considerably large amounts of type 3 poliovirus for long periods. One child in Infant Home B showed only transient excrection of the minimal detectable amount of virus on day 8. In Infant Home H the longest duration of virus excretion was 41 days with an average excretion period of 33.6 days, while in Infant Home B the longest duration of excretion was not less than 85 days with an average of 61.4 days. There was, however, no such great difference in the average of the maximal virus content per gram of stool of individual children between the two infant homes. This average was 107.4 TCD50 in the H institution and 107.1 TCD50 in the B. Stools of the contact children were examined only in Infant Homes H, where only one contact child excreted a small amount of virus on day 6.Circulating antibody response was good in all the vaccinees, except the one mentioned above in Infant Home B. This child and three contacts of Infant Home H, including the one mentioned above, showed no rise of circulating antibody. The contacts of Infant Home B were fed Sabin types 1 and 2 divalent vaccine one week after the commencement of the trial, but they showed only type 3 antibody response. This may indicate that efficient contact infection with the vaccine virus took place during the first week of the trial.Reversion of rct/40 character of virus progeny was observed rather early, and 45per cent of the isolates investigated was positive for rct/40 character, while only 14per cent was negative. The incidence of reversion appeared irregularly in individual children. Some children excreted rct/40± of ract/40+ virus early and again excreated rct/40- virus later.The results obtained indicated that the USOL-D bac virus multiplied well in the gut of children, who showed a good antibody response, although it was genetically unstable. Efficient contact infection was observed in one institution where children were in close contact with one another in a play-room. Contact infection was almost completely prevented in the other institution where children were kept in bed.The USOL-D bac virus was discussed for suitability as a candidate for a more acceptable type 3 poliovirus vaccine strain, in comparison with the Sabin type 3 Leon 12a1b virus.