EVALUATION OF SABIN LIVE POLIOVIRUS VACCINE IN JAPAN

IV. MARKER TESTS ON POLIOVIRUS STRAINS RECOVERED FROM VACCINEES AND THEIR CONTACTS

Abstract

T (rct) marker tests were carried out with a total of 364 strains, including 195 type 1, 51 type 2 and 118 type 3 poliovirus strains. Type 1 and type 2 strains were shown to be predominantly T^- in 82 and 77 %, respectively, and a few (1 and 6 %) were T⁺ strains, whereas type 3 strains were T^- at a low ratio of 25 % while 41 % thereof were T⁺. These findings indicate that, concerning the T marker, Sabin's type 1 and type 2 viruses are relatively stable, whereas the type 3 virus is rather unstable. Change from d^- to d^± or d⁺ of Sabin's vaccine viruses was also shown to be frequent; d^-, d^± and d⁺ strains were found in 23, 21 and 56 %, respectively, among 105 type 1 strains; in 15, 22 and 63% among 40 type 2 strains; and in 17, 17 and 65% among 52 type 3 strains.
These findings obviously indicate that the vaccine viruses do not remain con-stant genetically after multiplication in human beings. In relation to the safety of the vaccine, this information is of importance merely in the sense that the results of the marker tests are of value in selecting the strains for the neurovirulence test in monkeys, which supplies further information on the change in virulence of the vaccine viruses after human passages. It is evident, however, that the ultimate safety of the vaccine rests upon a long-term vigilance on the outcome of its use in the field.