Influenza and Influenza Vaccine

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• Influenza and Influenza Vaccine

Epidemiology and Prevention of Vaccine-Preventable
Diseases National Immunization Program Centers
for Disease Control and Prevention
Revised March 2002
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Influenza

• Highly infectious viral illness
• Epidemics reported since at least 1510
• At least 4 pandemics in 19th century
• Estimated 21 million deaths worldwide in pandemic
  of 1918-1919
• Virus first isolated in 1933

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Influenza Virus

• Single-stranded RNA virus
• Family Orthomyxoviridae
• 3 types A, B, C
• Subtypes of type A determined by hemagglutinin
  and neuraminidase

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Influenza Virus Strains

• Type A- moderate to severe illness - all age
  groups
• - humans and other animals
• Type B- milder epidemics - humans only -
  primarily affects children
• Type C- rarely reported in humans
• - no epidemics

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• Influenza Virus

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Influenza Antigenic Changes

• Structure of hemagglutinin (H) and neuraminidase
  (N) periodically change
• Shift Major change, new subtype
• Exchange of gene segment
• May result in pandemic
• Drift Minor change, same subtype
• Point mutations in gene May result in
  epidemic

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Examples of Influenza Antigenic Changes

• Antigenic shift
• H2N2 circulated in 1957-1967
• H3N2 appeared in 1968 and completely replaced
  H2N2
• Antigenic drift
• In 1997, A/Wuhan/359/95 (H3N2) virus was dominant
• A/Sydney/5/97 (H3N2) appeared in late 1997 and
  became the dominant virus in 1998

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• Influenza Type A Antigenic Shifts

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Impact of Pandemic Influenza

• 200 million people could be affected
• Up to 40 million require outpatient visits
• Up to 700,000 hospitalized
• 89,000 - 200,000 deaths

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Influenza Pathogenesis

• Respiratory transmission of virus
• Replication in respiratory epithelium with
  subsequent destruction of cells
• Viremia usually not demonstrable
• Viral shedding in respiratory secretions for 5-10
  days

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Influenza Clinical Features

• Incubation period 2 days (range 1-5 days)
• Severity of illness depends on prior experience
  with related variants
• Abrupt onset of fever, myalgia, sore throat,
  nonproductive cough, headache

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Influenza Complications

• Pneumonia
• primary influenza
• secondary bacterial
• Reye syndrome
• Myocarditis
• Death 0.5-1 per 1000 cases

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Impact of Influenza

• Highest rates of hospitalization among young
  children and person gt65 years
• Average of 114,000 influenza-related excess
  hospitalizations per year since 1969
• 57 of all hospitalizations among persons lt65
  years of age
• Greater number of hospitalizations during type A
  (H3N2) epidemics

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Impact of Influenza

• 20,000 excess deaths in each of 11 epidemics
  between 1972 and 1995
• gt40,000 excess deaths in 6 epidemics
• gt90 of deaths among persons gt65 years of age

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Influenza Diagnosis

• Clinical and epidemiological characteristics
• Isolation of influenza virus from clinical
  specimen (e.g., nasopharynx, throat, sputum)
• Significant risk in influenza IgG by serologic
  assay
• Direct antigen testing for type A virus

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Influenza Epidemiology

• Reservoir Human, animals (type A only)
• Transmission Respiratory
  Probably airborne
• Temporal pattern Peak December - March in
  temperate area May occur earlier or
  later
• Communicability Maximum 1-2 days before
  to 4-5 days after onset

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Month of Peak Influenza Activity United States,
1976-2001
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Influenza Vaccine

• Composition Split (subvirion) virus Trivalent
  (H3N2, H1N1, B)
• Efficacy Varies by similarity to
• circulating strain, age,
• underlying illness
• Duration ofImmunity lt1 year
• Schedule 1 dose annually

2 doses for first vaccination of children lt9
years
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Influenza Vaccine Efficacy

• 70 to 90 effective among persons lt65 years of
  age
• 30-40 effective among frail elderly persons
• 50-60 effective in preventing hospitalization
• 80 effective in preventing death

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• Influenza and Complications Among Nursing Home
  Residents

RR1.9
RR2.0
RR2.5
RR4.2
Genesee County, MI, 1982-1983
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Timing of Influenza Vaccine Programs

• Influenza activity peaks between late December
  and early March
• Optimal time for vaccination programs October
  through November
• First available vaccine should be targeted to
  persons at highest risk of complication of
  influenza

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Timing of Influenza Vaccine Programs

• Actively target vaccine available in September
  and October to persons at increase risk of
  influenza complications, children lt9 years, and
  health care workers
• Vaccination of all other groups should begin in
  November
• Continue vaccinating through December and later,
  as long as vaccine is available

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Influenza Vaccine 2001-2002

• A/Moscow/10/99 (H3N2)
• A/New Caledonia/20/99 (H1N1)
• B/Sichuan/379/99

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• Influenza Vaccine Schedule

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Influenza Vaccine Recommendations

• All persons 50 years of age or older
• Persons gt6 months of age with chronic illness
• Residents of long-term care facilities
• Pregnant women
• Persons 6 months to 18 years receiving chronic
  aspirin therapy

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Influenza Vaccine Recommendations

• Routine annual influenza vaccination for persons
  50 years and older
• Up to a third of persons 50-64 years have high
  risk conditions
• Only 35 received influenza vaccine in 1999
• May increase coverage in HCWs
• Reduced sick days

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Influenza Vaccine Recommendations

• Persons with the following chronic illnesses
  should be considered for influenza vaccine
• pulmonary (e.g., asthma, COPD)
• cardiovascular (e.g., CHF)
• metabolic (e.g., diabetes)
• renal dysfunction
• hemoglobinopathies
• immunosuppression, including HIV
• infection

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Pregnancy and Influenza Vaccine

• Risk of hospitalization 4 times higher than
  nonpregnant women
• Risk of complications comparable to nonpregnant
  women with high risk medical conditions
• Vaccination recommended if gt14 weeks gestation
  during influenza season

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HIV Infection and Influenza Vaccine

• Persons with HIV at higher risk of complications
  of influenza
• Vaccine induces protective antibody titers in
  many HIV infected persons
• Transient increase in HIV replication reported
• Vaccine will benefit many HIV-infected persons

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Influenza Vaccination of Children

• Children lt24 months at increased risk of
  hospitalization
• Vaccination of healthy children 6-23 months is
  encouraged
• Vaccination of household contacts and out-of-home
  caretakers is encouraged

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Influenza Vaccine Recommendations

• Health care providers, including home care
• Employees of long-term care facilities
• Household members of high-risk persons (including
  children 0-23 months)

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In the 2000 National Health Interview Survey,
only 38 of health care workers reported
receiving influenza vaccine in the previous 12
months.
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Influenza Vaccination of HCWs

• Educate HCWs about the benefits of vaccination
  for themselves, their families, and their
  patients
• Educate staff about vaccine adverse reactions
• Provide free vaccine at the work site to all
  employees, including night and weekend staff

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Influenza Vaccine Recommendations

• Providers of essential community services
• Foreign travelers
• Students
• Anyone who wishes to reduce the likelihood of
  becoming ill from influenza

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Influenza Vaccine Adverse Reactions

• Local reactions 15-20
• Fever, malaise uncommon
• Allergic reactions rare
• Neurological very rare reactions

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Influenza VaccineContraindications and
Precautions

• Severe allergy to vaccine component (e.g., egg,
  thimerosal) or following prior dose of vaccine
• Moderate to severe acute illness

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Influenza VaccineStrategies to Improve Coverage

• Ensure systematic and automatic offering of
  vaccine to high-risk groups
• Educate health care providers and patients
• Address concerns about adverse events
• Emphasize physician recommendation

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Influenza VaccineMissed Opportunities

• Up to 75 of persons at high risk for influenza
  or who die from pneumonia and influenza may have
  received care in a physician's office in the
  previous year.
• In one study all non-nursing home persons who
  died from pneumonia or influenza had at least one
  medical visit in the previous year.

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Influenza Antiviral Agents

• Amantadine and rimantadine
• effective against influenza A only
• approved for treatment and prophylaxis
• Zanamivir and oseltamivir
• neuraminidase inhibitors
• effective against influenza A and B
• oseltamivir approved for prophylaxis

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Live-attenuated, Cold-adapted Intranasal
Influenza Vaccine

• Vaccine efficacy 93 among children for influenza
  A (H3N2) and influenza B
• Vaccinated children had 21 fewer febrile
  illnesses
• Vaccinated children had 30 fewer episides of
  febrile otitis media

Belshe et al, NEJM 19983381405-12
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Live-attenuated, Cold-adapted Intranasal
Influenza Vaccine

• Safe and effective in children
• May increase influenza vaccine coverage among
  high-risk children
• Cost-effectiveness and impact of wider use among
  children unknown

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Influenza Surveillance

• Monitor prevalence of circulating strains and
  detect new strains
• Rapidly detect outbreaks
• Assist disease control through rapid preventive
  action
• Estimate influenza-related morbidity, mortality
  and economic loss

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National Immunization Program

• Hotline [phone]
• Email nipinfo_at_cdc.gov
• Website www.cdc.gov/nip