Experimental Immunization of Mice with the Virus of Epidemic Influenza

Abstract

Summary Mice were inoculated intraäbdominally with active or inactive influenza-virus and tested for immunity 14 days later with an intranasal dose between 1 and 10 MLD. The averaged results of a number of experiments show that the minimal immunizing dose of active virus of epidemic influenza (strain PR8) is approximately 250 intranasal MLD and of formolized inactive virus the equivalent of about 8000 intranasal MLD. A similar result with active and inactive virus was obtained with the strains Melbourne and PR8 grown in chick-embryo tissue-culture. The minimal immunizing dose of formolized virus-suspensions containing a small residuum of active virus is not appreciably greater than that of preparations containing no active virus except when the proportion of active virus exceeds 1 per cent of the total amount of virus. Centrifugation at 27,500 rpm sediments the immunizing material from formolized suspensions as completely as the active virus from untreated suspensions.