Why can we use currently available flu vaccine?
Currently available flu vaccines only protect against the currently circulating ordinary flu. The virus causing a pandemic will be so different from the strains in the vaccine that they are very unlikely to provide any significant immunity in a pandemic situation. New vaccine must be developed to match the new pandemic strain. Can any vaccine left from previous years be used? No. It will only provide protection against old strains of influenza virus, not against a new strain.
