Rct-marker tests on isolates from WM 3 and Sabin type 3 attenuated poliovirus vaccinees

Summary

The rct-marker test was performed on 129 and 33 virus isolates collected after oral vaccination with the live WM3 and Sabin type 3 vaccines, respectively. The main deviation of the WM3 isolates from the behavior of the original vaccine strain appeared during the first week after vaccination. The viruses isolated later showed few significant changes. Compared with the type 1 “CHAT” isolates investigated earlier the deviations from the pattern of the vaccine towards an improved replicative capacity at higher temperatures generally were more marked with the type 3 strain. The mean rct-ratios of WM3 and CHAT isolates tested at 35° C and 39.2°C, however, did not diverge markedly. The Sabin type 3 isolates did display at least a 10-fold higher growth capacity at 39.2°C compared with the WM3 and CHAT isolates. If less than a 2 log₁₀ difference between replicative capacity at 38.9°C or 39.2°C and 35°C is chosen as a criterion for the rct + character then 8 isolates out of 90 tested from 5 of 30 WM3 vaccinees displayed the rct + character at 38.9°C. No isolate out of 39 tested deriving from 13 WM3 vaccinees had the rct + character at 39.2°C, and 2 isolates from 1 vaccine out of 33 isolates tested from 10 Sabin type 3 vaccinees had the rct + character at 39.2° C. The corresponding figures of the CHAT strain isolates were 2 crt + isolates out of 144 tested.