Influenza

Influenza Overview for Health Professionals - May 2006

Influenza spreads easily, causing substantial morbidity and mortality. Influenza is a highly contagious virus that spreads easily via aerosolized or droplet transmission from infected to susceptible persons. In the U.S., annual attack rates are 5 to 20 percent of the population and influenza activity peaks from December to March (or later), with February being the most common peak month.

An average of 36,000 Americans die from influenza-related complications each year. Mortality is most common in elderly persons, but deaths do occur in other age groups, including children. Hospitalizations due to complications from influenza are highest at the extremes of age, with infants and toddlers hospitalized at rates comparable to elderly persons.

Vaccination is the primary means of prevention

The best way to protect against influenza is with annual vaccination. Vaccine efficacy is affected by the age and immune status of recipients and the match between vaccine and circulating influenza strains. The majority of children and young adults develop high antibody titer levels following vaccination, correlating with protection against similar circulating viral strains. Post-vaccination titers are lower in elderly persons and efficacy against influenza infection is lower in this population. While it may not prevent infection, among elderly persons not living in nursing homes or similar chronic-care facilities, influenza vaccine is 30 to 70 percent effective in preventing hospitalization for pneumonia and influenza. Influenza vaccine is 80 percent effective against influenza-related death in elderly persons.

Influenza onset is abrupt and complications can be severe

Following a one- to four-day incubation period (during which asymptomatic persons may transmit the virus), influenza is marked by abrupt onset of fever (up to 104ºF), myalgia, sore throat and a non-productive cough. Additional symptoms may include rhinorrhea, headache, chills, photophobia and malaise. Children may also exhibit symptoms uncommon in adults (e.g., diarrhea, vomiting and nausea).

The most common complication of influenza is secondary bacterial pneumonia. Influenza is also associated with other serious illnesses, including encephalopathy, Reyes syndrome, myocarditis and pericarditis. Hospitalization rates are similar in infants and toddlers and the elderly.

Influenza viruses mutate; annual vaccination is necessary

There are three basic influenza antigen types--A, B and C. Influenza C is rarely reported in humans; influenza B usually causes mild disease and primarily affects children; influenza A causes moderate to severe illness and affects all age groups.

The influenza A virus is also named by the type of H an N proteins it carries. The H and N proteins of the influenza virus can undergo minor changes or mutations, leading to new strains. Scientists call this change "antigenic drift." Drift is an ongoing process and is one way the virus evades the body's immune system. Immunity to one strain of influenza virus does not necessarily confer immunity to a new strain which has undergone antigenic drift.

When an antigenic shift happens, worldwide pandemic may occur if the new virus is easily transmitted between humans, most or all of whom would have minimal to no protection against the new strain. Antigenic shift led to three pandemics during the last century (1918-20, 1957-58, 1968-69). When drift occurs, those with previous exposures to similar virus strains (either through natural exposure or vaccination) will have incomplete protection.

The influenza vaccine is a trivalent combination including one influenza B and two influenza A strains. It is reformulated annually, with strains chosen by the FDA in collaboration with the World Health Organization to match the strains anticipated to circulate during the following season. Annual vaccination is necessary for optimal protection.

Influenza vaccines are safe

The inactivated vaccine has been available in the U.S. since the 1940s. It is approved for use in all persons 6 months of age and older. Mild and transient local reactions (e.g., soreness, induration, erythma) are the most common adverse events associated with inactivated vaccine. Systemic symptoms (e.g., fever, malaise, chills) are rare (<1 percent of vaccine recipients) and usually transient, lasting one to two days.

The live attenuated vaccine has been available for use in the U.S. since 2003. It is approved for use only in healthy persons 5 to 49 years of age. The live attenuated vaccine is not approved for use in anyone outside this age range or persons with asthma, reactive airway disease or other chronic pulmonary or cardiovascular conditions, metabolic disease (e.g., diabetes), renal disease, hemoglobinopathies (e.g., sickle cell disease), or immunosuppression; and children receiving long-term aspirin therapy. Anyone receiving the live vaccine should avoid close contact with immunocompromised persons for 21 days.

Neither the inactivated nor the live vaccine should be administered to anyone with a history of a severe reaction to the vaccine or severe systemic (e.g., anaphylactic) reaction to eggs or egg proteins.

All high-risk persons should be vaccinated annually

For optimal protection, the following persons should be vaccinated annually:

• Adults 50 years of age and older
• Children 6 through 59 months of age
  • Children younger than 9 years of age being immunized for the first time will require two vaccines at specific intervals (see prescribing information for product used for acceptable dosing intervals)
• Health care workers
• Anyone at least 6 months of age with certain risk factors, including
  • Asthma or other pulmonary disorder
  • Cardiovascular disease
  • Metabolic diseases (e.g, diabetes), renal dysfunction, hemoglobinopathies or immunosuppression
  • Conditions that can compromise respiratory function, handling of respiratory secretions or that increase risk for aspiration (e.g., cognitive dysfunction, spinal cord injuries, seizure disorders, other neuromuscular conditions)
  • Long-term aspirin therapy (for children 6 months to 18 years of age)
• Women who will be pregnant during influenza season
• Anyone who comes in direct contact with anyone at high-risk (including infants younger than 6 months who cannot themselves be vaccinated)
• Anyone wishing to reduce his or her risk of contracting influenza

Influenza Immunization Among Health Care Personnel - Call to Action

A new Call to Action encouraging health care personnel (HCP) to receive annual influenza vaccination has been issued by the National Foundation for Infectious Diseases (NFID). This new report cites Centers for Disease Control and Prevention (CDC) data revealing that 58 percent of HCP have not received their annual flu vaccine.

The Call to Action also includes key steps that health care institutions can take to ensure that their workers are vaccinated against influenza. Click below to access the report, which highlights key insights on the current HCP environment.

NFID plans to use this Call to Action as a key resource in educating HCP about the effects of influenza and alerting them to the actions they can take to prevent themselves, employees and their patients from contracting this highly contagious infection.

NFID's Improving Influenza Vaccination Rates in Health Care Personnel initiative is made possible by an unrestricted educational grant to NFID from sanofi pasteur.

Influenza Immunization Among Health Care Personnel - Call to Action