BOD - Revision - Michaelmas - Smith - Viruses Lecture 17. INFLUENZA AND HEPATITIS VIRUSES Influenza Virus 1. Treatment: anti-influenza drugs, vaccines · Amantadine and rimantidine: inhibit entry by blocking M2 proton channel so uncoating can't occur * However, M2 mutations rapidly confers resistance to these drugs * These are effective against influenza A · Tamiflu (oseltamivir phosphate) and Relenza (zanamivir): inhibit NA Tamiflu is an analogue of sialic acid and inhibits neuraminidase so that influenza virus cannot be released from the infected cell. The virus also clumps to itself because HA and NA are glycoproteins. These effective against influenza A and B Currently, the majority of circulating influenza viruses are resistant to the adamantanes and WHO recommends neuraminidase inhibitors as the first-line treatment for people requiring antiviral therapy. · Influenza vaccine: Unlike many other natural viral infections (e.g. measles, mumps, chicken pox, etc.), infection by influenza viruses does not provide life-long protective immunity against subsequent infections with related viruses. * In the immune response, HA-specific antibodies in serum and in the respiratory tract neutralize the virus and prevent infection, while the T cell response is important for viral clearance and host recovery. * The absence of life-long protective immunity has been attributed primarily to the extensive antigenic diversity that exists among the influenza viruses to which a person is exposed to during a lifetime. * Each year, the viruses that are most likely to cause flu are identified in advance and vaccines are made to match them as closely as possible. The vaccines are recommended by the World Health Organization (WHO). * WHO recommends annual vaccination for: " pregnant women at any stage of pregnancy " children aged between 6 months to 5 years " elderly individuals (aged more than 65 years) " individuals with chronic medical conditions health-care workers * Currently, both inactivated influenza vaccines (IIVs) and live attenuated influenza vaccines (LAIVs) have been developed and approved for use. Most IIVs are administered either intramuscularly or intradermally, and LAIVs are administered intranasally. " Immunization with all currently approved IIVs is based primarily on inducing an antibody response to the antigenically variable HA protein.
" Although the immune response to LAIVs is more complex and involves both T cell and antibody responses, these vaccines also work best when the HAs in the vaccine match those of circulating viruses. * Most injected flu vaccines protect against three types of flu virus: " A/H1N1 - the strain of flu that caused the swine flu pandemic in 2009 " A/H3N2 - a strain of flu that mainly affects the elderly and people with risk factors like a long term health condition. In 2017/18 the vaccine will contain an A/Hong Kong/tt801/201tt H3N2-like virus Influenza B - a strain of flu that particularly affects children. In 2017/18 the vaccine will contain B/Brisbane/60/2008-like virus " The nasal spray flu vaccine and some injected vaccines also offer protection against a fourth B strain of virus, which in 2017/18 is the B/Phuket/3073/2013-like virus. * The most important