difficulty in preparations and the role of antigenic variations

1. PRESENTED BY:
DR RANI KOMAL LATA
MPH 2015-17( 2ND SEM)1
Amity Institute of Virology and Immunology

2.  Influenza, commonly known as ‘the flu’
 Serious contagious respiratory illness that is
caused by influenza viruses
 It can cause mild to severe illness and at times,
can result in hospitalization or death.
 Some people, such as older people, young
children, and people with certain health
conditions, are at high risk for serious flu
complications.
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3.  Single-stranded RNA virus : Orthomyxoviridae family
 3 types: A, B, C
 Subtypes of type A determined by :
 hemagglutinin and neuraminidase
 Influenza Virus Strains :
 TYPE A:
 moderate to severe illness
 all age groups
 humans and other animals
 TYPE B
 milder disease primarily affects
children & humans only
 TYPE C
 rarely reported in humans
 no epidemics
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5.  The name “influenza” originated in 15th century
Italy, from an epidemic attributed to “influence of
the stars.”
 First pandemic in 1580
 At least 4 pandemics in 19th century
 Estimated 21 million deaths worldwide in
pandemic of 1918-1919
 Virus first isolated in 1933
5 www.cdc.gov/flu

6. 1. 1918-19 “Spanish flu” H1N1
2. 1957 “Asian flu” H2N2
3. 1968 “Hong Kong flu” H3N2
4. 1976 “Swine flu” episode H1N1
5. 1977 “Russian flu” H1N1
6. 1997 “Bird flu” in HK H5N1
7. 1999 “Bird flu” in HK H9N2
8. 2003 “Bird flu” in Netherlands H7N7
9. 2004 “Bird flu” in SE Asia H5N1
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www.flu.gov/pandemic/history/

7.  The number of influenza associated deaths varies
substantially by: year, influenza virus type and
subtype, and age group
 Annual influenza associated deaths ranged from
3,349 (1985-86 season) to 48,614 (2003-04
season), with an average of 23,607 annual deaths
 Persons 65 years of age and older account for
approximately 90% of deaths
 2.7 times more deaths occurred during seasons
when A(H3N2) viruses were prominent
7 “The Economic Impact of Pandemic
Influenza in the United States”

8.  Inactivated subunit (IIV) : intramuscular or intradermal
 Live attenuated vaccine (LAIV) : intranasal
 Trivalent vaccine : contains three inactivated viruses:
1. Type A(H1N1)
2. Type A(H3N2)
3. Type B
 Quadrivalent influenza vaccines:
 introduced for the 2013-2014 season.
 contain the same antigens as trivalent vaccines
 with the exception that quadrivalent vaccines contain two type B
strains.
 Vaccine viruses are grown in chicken eggs, and the final product
contains residual egg protein.
 The vaccine is available in both pediatric (0.25-mL dose) and adult
(0.5-mL dose) formulations.
8 www.cdc.gov/vaccines

9.  One vaccine contains multiple
inactive strains of the virus.
 Once administered, the human
immune system builds
antibodies that recognize these
dead flu strains.
 That way when the active flu
virus enters the body, the
immune system is able to
recognize the invader and
defend itself
 Flu vaccines cause humoral
antibodies levels to develop in
the body about two weeks after
vaccination.
 These antibodies provide
protection against infection with
the viruses that are in the
vaccine.
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10.  The two most important structural proteins
demonstrating genetic and antigenic variation which are
relevant to protection and vaccination are the envelope
glycoproteins, “the haemagglutinin (HA) and the
neuraminidase (NA)”.
 HA is particularly important: as it mediates virus
attachment to the host cell and antibody induced against
the HA neutralises virus infectivity.
 The NA is involved in elution of virus from cells and the
spread of infection between cells
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11.  INFLUENZA VIRUSES EVADE HOST IMMUNE
RESPONSE
 THEY EVOLVE TWO DIFFERENT MECHANISMS
TO GENERATE ANTIGENIC VARIATION
 CHANGED SURFACE ANTIGENS ESCAPE
HOST IMMUNE REPONSE
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12.  It is a mechanism for variation in viruses that involves the accumulation of
mutations within the genes that code for antibody-binding sites.
 This results in a new strain of virus particles which cannot be inhibited as
effectively by the antibodies that were originally targeted against previous
strains.
 Viruses that are closely related to each other usually share the
same antigenic properties and an immune system exposed to an similar
virus will usually recognize it and respond, sometimes called cross-
protection.
 But these small genetic changes can accumulate over time and result in
viruses that are antigenically different (When this happens, the body’s
immune system may not recognize those viruses)
 Genetic changes that result in a virus with different antigenic properties is
the main reason why people can get the flu more than one time.
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14.  It is the process by which two or more different strains of a virus, or
strains of two or more different viruses, combine to form a new
subtype having a mixture of the surface antigens of the two or more
original strains. This is a specific case of reassortment.
 An abrupt, major change in the influenza A viruses, resulting in new
hemagglutinin and/or new hemagglutinin and neuraminidase
proteins in influenza viruses that infect humans.
 Such a “shift” occurred in the spring of 2009, when an H1N1 virus
with a new combination of genes emerged to infect people and
quickly spread, causing a pandemic.
 When shift happens, most people have little or no protection against
the new virus.
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17.  Understanding the genetic diversity of viral
pathogens and how it is modulated by host
immunity, transmission, epidemic dynamics and
population structures is essential for the
development of effective control measures.
 Effective vaccination against such viruses requires
surveillance programmes to monitor circulating
serotypes and their evolution to ensure that
vaccine strains match field viruses.
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