Interference between cold-adapted (ca) influenza A and B vaccine reassortants or between ca reassortants and wild-type strains in eggs and mice.

Interference between pairs of cold-adapted (ca) influenza A and B vaccine reassortant viruses and between ca influenza B reassortant viruses and wild-type influenza strain A/PR/8/34 was studied in embryonated eggs and/or in the respiratory tract of three strains of mice. Interference in eggs between ca A and B reassortants occurred after 2 days but was masked by later cycles of growth. When doses of 10(6) EID50 of the reassortant viruses B/60/32/R and A/47/6/R were administered to outbred mice, interference with the growth of A/47/6/R occurred in the turbinates; interference with the growth of B/60/32/R did not occur. However, interference with the growth of B/60/32/R was noted in the lungs of Balb/c mice after co-infection with 10(6) EID50 of both A/PR/8/34 and B/60/32/R. Interference did not occur when the dose of B/60/32/R was increased to 10(7) EID50 per mouse. When CBA mice were co-infected with 10(6) EID50 of both B/60/32/R and the influenza A ca reassortant R/34, or 10(6) EID50 of B/60/32/R,R/34 and A/Leningrad/134/57, interference did not occur. Interference could not be detected in mice following dual infection from serum responses to individual viruses.