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About Influenza Vaccine

Each year in September and February respectively, the WHO Global Influenza Program announces the influenza strains for production of the next seasonal vaccines. The disease season generally begins in May–June in the southern hemisphere and in November–December in the northern hemisphere.

 

  

 

 

 

 

 

 

 

The identification of strains is based on surveillance data from the worldwide network of national influenza centers and WHO collaborating centers. Current seasonal influenza vaccines contain antigens from two A subtypes, H3N2 and H1N1, and one type B virus.

 

Vaccine Types

The majority of the currently available licensed seasonal influenza vaccines are prepared using eggs for the following vaccine types. However, some manufacturers employ cell culture for the production of their vaccines.

1. Whole virus vaccines consisting of inactivated viruses.

2. Split virus vaccines consisting of inactivated virus particles disrupted by detergent treatment.

3. Subunit or surface antigen vaccines consisting essentially of purified hemagglutinin and neuraminidase from which other virus components have been removed.

4. Live attenuated (cold-adapted) virus vaccines consisting of weakened (non-pathogenic) whole virus.

 To produce the split virus and subunit vaccines the whole virus is subjected to disruption with a surfactant, which solubilizes the viral membrane. For subunit vaccines the internal subviral core of the virus is separated from the surface proteins on the basis of their differing sedimentation rates. With split virus vaccines, the choice and use of surfactant ensures that the subviral core itself is disassembled.

The live virus vaccines are formulated to contain 106.5-7.5 median tissue culture infectious doses of live attenuated influenza virus reassortants of the strains recommended by the U.S. Public Health Service for the upcoming influenza season. The reassortants comprise the hemagglutinin and neuraminidase from the desired wild type strains with the remaining influenza genes originating from a “cold adapted” parent. With cold-adaptation the virus replicates efficiently at 25°C but is restricted in replication at 37-39°C. Thus the virus can replicate in the nasopharynx, thereby inducing protective immunity, but is prevented from infecting the upper and lower respiratory tract.

 

The live virus vaccines are formulated to contain 106.5-7.5 median tissue culture infectious doses of live attenuated influenza virus reassortants of the strains recommended by the U.S. Public Health Service for the upcoming influenza season. The reassortants comprise the hemagglutinin and neuraminidase from the desired wild type strains with the remaining influenza genes originating from a “cold adapted” parent. With cold-adaptation the virus replicates efficiently at 25°C but is restricted in replication at 37-39°C. Thus the virus can replicate in the nasopharynx, thereby inducing protective immunity, but is prevented from infecting the upper and lower respiratory tract.

Some licensed seasonal influenza mammalian cell culture vaccines are now available in Europe.