New vaccine could be used to treat H5N1, H9 bird flu strains
The vaccine, which uses a "live" virus as opposed to a "killed" virus and is administered via nasal spray, has proven to be highly effective against the bird flu strains in both mice and ferrets. Killed viruses are broken down using chemicals or heat and are injected directly into the bloodstream, ScienceDaily reports.
Because killed virus vaccines are deemed safer than attenuated or "live" virus vaccines, they are used more often. Attenuated virus vaccines have the potential to exchange genetic information with viruses that are generally associated with annual outbreaks, which could cause a lethal but hard to transmit virus more transmissible among humans.
To make the attenuated vaccine safer, researchers at the University of Maryland worked off of the principle that flu viruses carry their genetic information in eight different segments. When viruses re-assort, they exchange segments, all of which are unique and all of which are required in the process. Viruses are unfit, however, if they contain more than eight segments, according to ScienceDaily.
The vaccine, which is based on an attenuated version of the H9 virus strain, had an H5 gene inserted into one segment of the H9 virus to confer immunity to the H5 virus. Segment 8 of H9, which is comprised by NS1 and NS2 genes, was broken apart, and the NS2 gene was transferred to segment 2 next to the polymerase gene, which makes copies of the virus' genetic information during replication.
The insertion of the NS2 gene next to the polymerase gene slowed its function, thereby interfering with viral replication and making the vaccine safer. Additionally, the H5 gene was inserted into segment 8, where the missing NS2 gene used to be, ScienceDaily reports.
Because the NS1 and NS2 genes were separated and both are key elements of viral replication, the likelihood of successful re-assortment is reduced because it would require both separated gene segments instead of one segment containing both genes.
The World Health Organization lists H5, H7 and H9 bird flu strains as potential pandemic viruses because they have all caused human infection, though the occurrence is rare, according to ScienceDaily.