Figure 6.

Growth characteristics of wild-type B/Yamagata, B/201, and B/234 viruses in embryonated eggs. One hundred pfu of influenza B viruses was injected into the allantoic cavity of embryonated eggs and incubated at 35°C for 72 h. Allantoic fluid was then harvested and subjected to HA analysis. Graph represents the average reciprocal HA dilution of two to six eggs for each virus. Asterisks indicate that two eggs were tested and gave the same HA titer. Influenza B/234 virus showed no HA titers in 8- and 10-day-old eggs.