[Criteria of primary screening of attenuated strains for live vaccine against Influenza A].

Reassortant strains for live influenza vaccine (LIV) were selected using two additional markers: intensity of cytopathic effect (CPE) at 40 degrees C in MDCK cells and toxicity for mice (induction of acute hemorrhagic pulmonary edema after intranasal challenge with undiluted virus). All wild-type viruses induced a high CPE in MDCK cells, while the reassortants differed by this sign. Only vaccine strains and attenuation donors were characterized by a low CPE. Modern epidemic viruses are highly toxic for mice, causing the death of 60-100% animals from hemorrhagic pulmonary edema on days 3-4 after intranasal infection. Attenuation donors and vaccine strains were not toxic for mice, the level of toxic effect correlating with CPE in MDCK culture. Evaluation of CPE in MDCK culture and toxicity for mice can be used for primary screening of candidates for LIV.