[Test of the potency of trivalent oral polio vaccines: comparison of 2 methods of reading]. / Prueba de potencia de vacunas antipoliomielíticas orales trivalentes: comparación de dos métodos de lectura.

Trivalent oral poliovaccine is used in Argentina to prevent poliomyelitis. Its potency is tested by infectivity titration of the three viruses in susceptible cell cultures (Hep-2 cell line). In order to compare the conventional reading method of cytopathic effect (CPE) with the staining technique of cell monolayers with crystal violet-formol, the reference viruses and several lots of trivalent vaccines were titrated. Between 3 and 10 days post-infection (pi) the plates were read under microscope and immediately stained. The maximum viral titer was reached at 5-7 days pi and additional CPE after this period did not alter the results. An incomplete monolayer confluence or cell aging (6-7 days pi) resulted in a poor definition between positive and negative cultures when the staining test was used. By contrast, CPE was easily read by microscope observation. Therefore, the staining method should only be considered for vaccine titration as a possible alternative when an inverted microscope is lacking or a great number of plates has to be read. In this case, to stain at day 7 pi is recommended.