Influenza and Influenza Vaccine

Epidemiology and Prevention of Vaccine-Preventable Diseases

National Center for Immunization and Respiratory Diseases

Centers for Disease Control and Prevention

Revised May 2009

Influenza Antigenic Changes

• Antigenic Shift

–major change, new subtype

–caused by exchange of gene segments

–may result in pandemic

• Example of antigenic shift

–H2N2 virus circulated in 1957-1967

–H3N2 virus appeared in 1968 and completely replaced H2N2 virus

Influenza Antigenic Changes

• Antigenic Drift–minor change, same subtype–caused by point mutations in gene–may result in epidemic

• Example of antigenic drift–in 2002-2003, A/Panama/2007/99

(H3N2) virus was dominant–A/Fujian/411/2002 (H3N2) appeared

in late 2003 and caused widespread illness in 2003-2004

Influenza Clinical Features

• Incubation period 2 days (range 1-4 days)

• Abrupt onset of fever, myalgia, sore throat, nonproductive cough, headache

• Severity of illness depends on prior experience with related variants

Influenza Complications

• Pneumonia

–secondary bacterial

–primary influenza viral

• Reye syndrome

• Myocarditis

• Death 0.5-1 per 1,000 cases

Impact of Influenza-United States, 1990-1999

• Approximately 36,000 influenza-associated deaths during each influenza season

• Persons 65 years of age and older account for more than 90% of deaths

• Higher mortality during seasons when influenza type A (H3N2) viruses predominate

• Highest rates of complications and hospitalization among young children and person 65 years and older• Average of more than 200,000

influenza-related excess hospitalizations • 57% of hospitalizations among

persons younger than 65 years of age• Greater number of hospitalizations

during type A (H3N2) epidemics

Impact of Influenza-United States, 1990-1999

Influenza Among School-Aged Children

• School-aged children

–typically have the highest attack rates during community outbreaks of influenza

–serve as a major source of transmission of influenza within communities

Month of Peak Influenza Activity United States, 1976-2008

0

5

10

15

20

25

30

35

40

45

50

Dec Jan Feb Mar Apr May

Pe

rce

nt

13%

19%

47%

13%

3% 3%

MMWR 2006;55:22

Influenza Vaccines

• Inactivated subunit (TIV)–intramuscular–trivalent–split virus and subunit types–duration of immunity 1 year or less

• Live attenuated vaccine (LAIV)–intranasal–trivalent–duration of immunity at least 1 year

Inactivated Influenza Vaccine Efficacy

• 70%-90% effective among healthy persons younger than 65 years of age

• 30%-40% effective among frail elderly persons

• 50%-60% effective in preventing hospitalization

• 80% effective in preventing death

05

10152025303540

Illness

Perc

en

t

0

2

4

6

8

10

Hosp Pneu Death

Per

cen

t

Influenza and Complications Among Nursing Home Residents

Vaccinated* Unvaccinated

RR=1.9 RR=2.0 RR=2.5 RR=4.2

*Inactivated influenza vaccine. Genesee County, MI, 1982-1983

LAIV Efficacy in Healthy Children

• 87% effective against culture-confirmed influenza in children 5-7 years old

• 27% reduction in febrile otitis media (OM)

• 28% reduction in OM with accompanying antibiotic use

• Decreased fever and OM in vaccine recipients who developed influenza

LAIV Efficacy in Healthy Adults

• 20% fewer severe febrile illness episodes• 24% fewer febrile upper respiratory

illness episodes• 27% fewer lost work days due to

febrile upper respiratory illness• 18%-37% fewer days of healthcare

provider visits due to febrile illness• 41%-45% fewer days of antibiotic use

Timing of Influenza Vaccine Programs

• Influenza activity can occur as early as October

• In more than 80% of seasons since 1976, peak influenza activity has not occurred until January or later

• In more than 60% of seasons the peak was in February or later

Timing of Influenza Vaccine Programs

• Providers should begin offering vaccine soon after it becomes available, if possible by October

• To avoid missed opportunities for vaccination, providers should offer vaccine during routine healthcare visits or during hospitalizations whenever vaccine is available

Inactivated Influenza Vaccine Schedule

AgeGroup

6-35 mos

3-8 yrs

>9 yrs

Dose0.25 mL

0.50 mL

0.50 mL

No.Doses1* or 2

1* or 2

1

*Only one dose is needed if the child received 2 doses of influenza vaccine during the previous influenza season

Influenza Vaccination of Children

• Children 6 months through 8 years of age who did not receive the recommended second dose of influenza vaccine in the initial year that they received influenza vaccine should receive 2 doses during the next influenza season*

• Children 6 months through 8 years of age who are being vaccinated two or more seasons after receiving an influenza vaccine for the first time should receive a single annual dose, regardless of the number of doses administered previously

*applies only to the influenza season that follows the first season that a child younger than 9 years receives influenza vaccine

Influenza Vaccination Schedule

• All children younger than 9 years receiving seasonal influenza vaccine for the first time this season should receive 2 doses, separated by 4 weeks

• Children younger than 9 years who received a seasonal vaccine for the first time last season but who received only 1 dose should receive 2 doses this season

MMWR 2010;59 (early release) From the Immunization Update 2010 webcast (originally broadcast August 5, 2010

Influenza Vaccination Schedule

• Children younger than 9 years who did not receive at least 1 dose of a 2009 monovalent vaccine should receive 2 doses of seasonal vaccine this season

• Children younger than 9 years whose 2009 pandemic vaccine history is not known should receive 2 doses this season

MMWR 2010;59 (early release) From the Immunization Update 2010 webcast (originally broadcast August 5, 2010

Live Attenuated Influenza VaccineIndications

• Healthy*, nonpregnant persons 2 through 49 years of age, including

–healthy children

–healthcare personnel

–persons in close contact with high-risk groups

–persons who want to reduce their risk of influenza

*Persons who do not have medical conditions that increase their risk for complications of influenza

Fluzone High-Dose TIV

• Approved only for persons 65 years of age or older

• Each dose contains 4 times as much hemagglutinin as the regular formulation of Fluzone for adults

• ACIP has not expressed a preference for the high dose Fluzone formulation or any other inactivated vaccine for use in persons 65 years and older

MMWR 2010;59 (early release) From the Immunization Update 2010 webcast (originally broadcast August 5, 2010

Inactivated Influenza Vaccine Adverse Reactions

Local reactions 15%-20%

Fever, malaise not common

Allergic reactions rare

Neurological very rare reactions

Live Attenuated Influenza VaccineAdverse Reactions

• Children–no significant increase in URI symptoms,

fever, or other systemic symptoms–significantly increased risk of asthma or

reactive airways disease in children 12-59 months of age

• Adults–significantly increased rate of cough, runny

nose, nasal congestion, sore throat, and chills reported among vaccine recipients–no increase in the occurrence of fever

• No serious adverse reactions identified

Inactivated Influenza VaccineContraindications and Precautions

• Severe allergic reaction to a vaccine component (e.g., egg) or following a prior dose of vaccine

• Moderate or severe acute illness

• History of Guillian Barré syndrome within 6 weeks following a previous dose of TIV (precaution)

Live Attenuated Influenza VaccineContraindications and Precautions

• Children younger than 2 years of age*

• Persons 50 years of age or older*

• Persons with chronic medical conditions*

• Children and adolescents receiving long-term aspirin therapy*

*These persons should receive inactivated influenza vaccine

Live Attenuated Influenza VaccineContraindications and Precautions

• Immunosuppression from any cause*

• Pregnant women*

• Severe (anaphylactic) allergy to egg or other vaccine components

• History of Guillian-Barré syndrome

• Children younger than 5 years with recurrent wheezing*

• Moderate or severe acute illness

*These persons should receive inactivated influenza vaccine