Treatment and Prophylaxis of Influenza-Influenza vaccines
Influenza is extremely contagious. For non-specific prophylaxis patient’s isolation, air decontamination, rooms ventilating and disinfection significantly prevent the spread of influenza.
Adamantan derivatives (amantadine hydrochloride and rimantadine) were introduced long ago for specific antiviral therapy of influenza type A. They should be administered only in 1-2 days after the disease onset. The drugs block M2 viral proteins thus preventing the step of virus uncoating. Hence, they are not so effective at the late stages of the disease. Also these medicals can be used for the urgent prophylaxis of influenza during epidemic period. Unfortunately, the rise of resistance of type A viruses to adamantan derivatives is common (e.g., pandemic “swine flu” А/2009/Н1N1 agent was totally resistant to these drugs).
Inhibitors of neuraminidase (e.g., oseltamivir and zanamivir) prevent the release of type A viruses. Overall, the treatment with oseltamivir shortens the total course of influenza A case for about 1 day.
As the result, vaccination is the only actual method to combat influenza epidemics.
For specific prophylaxis various anti-influenza vaccines were elaborated.
From the large number of vaccines the most efficient are live attenuated vaccines, inactivated split vaccines and subunit vaccines.
All of them are combined polyvaccines containing at least 3-4 various antigens of influenza viruses.
Live attenuated vaccines are usually produced by virus culture in embryonated eggs with subsequent virus purification. They confer protective type-specific immunity against the disease. Live vaccines can be administered locally by nasal spray. However, they are contraindicated for the persons suffering from egg protein allergy.
“Split” vaccines include viral particles (virions) decomposed by detergents. Detergent treatment removes lipid envelope from complex viruses, thus exposing inner protein antigens to the immune cells on vaccination. Influenza split vaccines contain viral coats (capsids) with immunogenic outer proteins (namely, hemagglutinin and neuraminidase).
The most advanced products are subunit vaccines. They are composed of different combinations of purified hemagglutinin and neuraminidase glycoproteins (e.g. Grippol or Fluorix vaccines). These vaccines are safe and strong effective. The latter makes possible the rapid change of vaccine composition according to current epidemic situation.
The individual efficacy of anti-influenza vaccines is 60-90%. Vaccination coverage of population in the range of 70-80% (“herd” or community immunity) prevents the emergence of seasonal influenza epidemic Nevertheless, post-vaccination immunity lasts only for 6-10 months. Together with possible changes of antigenic composition of epidemic virus it requires the regular design of new versions of influenza vaccines and annual human revaccination.