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

Impact of Influenza-United States, 1990-1999 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

Influenza Among 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 47% 19% 13% 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 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

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 Dose 0.25 mL 0.50 mL Age Group 6-35 mos 3-8 yrs >9 yrs No. Doses 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 Vaccine Indications 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 Vaccine Adverse 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 These symptoms were reported in 10 to 40 percent of both vaccine and placebo recipients. LAIV not licensed for children <60 months of age.

Inactivated Influenza Vaccine Contraindications 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 Vaccine Contraindications 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 Vaccine Contraindications 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