EPIDEMIOLOGY OF INFLUENZA

1. EPIDEMIOLOGY OF
INFLUENZA
DR. MAHESWARI JAIKUMAR.
maheswarijaikumar2103@gmail.com

2. INFLUENZA
• Influenza is an acute respiratory
tract infection caused by
INFLUENZA VIRUS (which is of 3
types) : A, B, and C.

4. • At present three types of
influenza viruses are circulating
in the world.
• A (H1N1), A (H3N2) and B virus.

7. • Influenza virus are classified
within the family
ORTHOMYXOVIRIDAE.
• There three viruses are
antigenitically distinct.

9. • Influenza A virus has 2 distinct
surface antigens – the
haemagglutinin (H) and the
neuraminidase (N) antigens.

11. RESEVOIR OF INFECTION
• Major reservoir of human
influenza virus exists in animals
and birds.

12. SOURCE OF INFECTION
• A case or subclinical case is the
source of infection.

13. PERIOD OF INFECTIVITY
• Virus is present in the
nasopharynx from 1 to 2 days
before and 1 to 2 days after the
onset of symptoms.

15. AGE & GENDER
• Influenza affects all ages and both
gender.
• Attack rate is lower among adults
and children constitute an
important link in the transmission
chain.

16. HUMAN MOBILITY
• Is considered to be an important
factor in the spread of infection.

17. IMMUNITY
• Immunity to influenza is subtype
specific. Antibodies against HA
and NA are important in
immunity to influenza.

18. • Antibodies appear in about 7
days after the attack and reach a
maximum level in about 2
weeks.

20. SEASON
• The seasonal incidence is striking.
Epidemics usually occur in winter
months in the northern
hemisphere.
• In tropical countries the virus
circulates throughout the year,
with one or two peaks in the
winter.

21. OVERCROWDING
• Enhances transmission.
• The attack rates are high in close
population groups; schools,
institutions, ships, etc.,

22. MODE OF TRANSMISSION
• Influenza spread mainly from
person to person by droplet
infection or droplet nuclei
created by sneezing, coughing
or talking.

23. • The portal of entry of the virus is
through respiratory tract

24. INCUBATION PERIOD
• 18 to 72 hours.

25. PATHOGENESIS & CLINICAL
FEATURES
• The virus enters the respiratory
tract and causes inflammation
and necrosis of superficial
epithelium of the tracheal and
bronchial mucosa, followed by
secondary bacterial invasion.

26. • There is no viraemia.
• The symptoms include fever,
chills, aches and pains, coughing
and generalized weakness.

29. • Fever lasts from 1-5 days, averaging
3 days in adults.
• Frequent complications are acute
sinusitis, otitis media, purulent
bronchitis and pneumonia.

31. • The most dreaded complication
is pneumonia, which should be
suspected if the fever persists
beyond 4 or 5 days or recurs
abruptly after convalescence.

33. • Ray’ Syndrome (Fatty liver with
encephalopathy) is a rare and
severe complication of influenza
(common in children).This
condition often progresses to
hapatic failure.

35. LABORATORY DIAGNOSIS
• IS DONE BY :
1.Virus isolation
2.Serology
3.ELISA

36. VIRUS ISOLATION
• Nasopharyngeal secretions are
the best specimens for obtaining
large amounts of virus infected
cells.

37. • The virus can be detected by the
indirect fluorescent antibody
technique.

38. SEROLOGY
• Serological test using
heamagglutination inhibition
(H1) and ELISA.
• ELISA test is more accurate than
others.

39. PREVENTION
• Optimal preventive measures
include:
• Good ventilation of public
buildings.
• Avoidance of crowded places
during epidemics.

40. PROTECTION AT INDIVDUAL
LEVEL

41. • Encouraging the sufferers to
cover their faces with
handkerchief when coughing,
sneezing.
• To stay at home at the first sign
of influenza.

43. • The vaccine is not recommended to
control spread in the general
population.
• In view of changing antigenic
structures (antigenic shift,
antigenic drift) new vaccines are
constantly required.

44. • Since epidemics of influenza are
unpredictable, the hope of
preventing influenza epidemics
by prophylactic mass vaccine is
remote.

45. • Since influenza vaccines will not
control epidemics, they are
recommended only in certain
selected population groups
(industry to reduce absenteeism
and among public servants to
prevent disruption of critical
public services – police force,
transport, medical.)

46. INFLUENZA VACCINE
• KILLED VACCINE
• Most influenza vaccination
programmes make use of
inactivated vaccines.

48. • The recommended vaccine
strains for vaccine production
are grown in the allantoic cavity
of developing chick embryos,
harvested, purified, killed by
formalin or beta–propiolactone,
and standardized according to
the haemagglutinin.

49. • The vaccine is conventionally
formulated in aqueous or saline
suspension.
• One dose of the vaccine contains
approximately 15 micrograms of
Ha.

51. • The vaccine is administered by
the subcutaneous or
intramuscular route.
• A single inoculation (0.5 ml for
adults and children over 3 years
and 0.25 ml for children from 6
months to 36 months of age is
usually given.

53. DEEP MUSCULAR INJECTION

54. • After vaccination there is an
increase in the serum antibody
in about 2 weeks.
• The protective value of the
vaccine varies between 70-90 %.

55. • Re vaccination on annual basis is
recommended.

56. LIVE ATTENUATED
VACCINES
• A trivalent, live attenuated
influenza vaccine administered
as a single dose intranasal spray
is an effective as inactivated
vaccine in preventing influenza.

58. NASAL SPRAY

60. • It is approved for use in
otherwise healthy individuals
between the age of 2 and 49
years.

61. • Because the risk of transmission of the
live attenuated vaccine virus to
immunocompromised individuals is
unknown, …….
• It should not be used in household
members of immunosuppressed
individuals, health care workers or
others with close contact with
immunosuppressed individuals

62. CONTRAINDICATIONS
• Vaccine should not be administered to :
• People who have severe allergy to
chicken egg.
• Individuals with anaphylactic reactions.
• Individuals with Guillain Barre
Syndrome.
• Children less than 6 months.

63. ANTIVIRAL DRUGS
• Due to the limitations in the
efficacy of influenza vaccines
antiviral drugs have been tried
for the prophylaxis and therapy.

64. • Two neuraminidase inhibitors
(ZANAMAVIR, OSELTAMIVIR) are
available for prophylaxis and
treatment of influenza A and B.
• The dose of oseltamivir is 75 mg
per day for prophylaxsis & 75 mg
twice daily for 5 days for therapy.

66. • Zanamivir is administered by
inhaler (10 mg dose) and is given
twice daily for therapy and once
daily for prophylaxsis.

67. CURRENT RECOMMENDATION
OF TREATMENT FOR
INFLUENZA “A”
• Zanamivir or a combination of
oseltamivir and rimantadine.

68. CURRENT RECOMMENDATION
OF TREATMENT FOR
INFLUENZA “B”
• Either oseltamivir or zanamivir.

69. FOR CHEMOPROPHYLAXSIS
• Against influenza A, zanamivir
should be used.
• If it is contraindicated
rimantadine can be used.

70. • In outbreak associated with
influenza B, either oseltamavir or
zanamivir can be used for
prophylaxsis.

71. THANK YOU