INTRODUCTION

Influenza (flu) can be a serious illness for people of any age. Every year, more than 200,000 people across the United States are hospitalized and at least 36,000 people die as a result of the flu ^{[1, 2]}. From 1999-2003, 70 influenza-associated deaths occurred in New Jersey residents ^[3]. In the United States, annual epidemics of influenza typically occur during the fall or winter months, but the peak of influenza activity can occur as late as April or May (Figure 1). Rates of infection are highest among children, but rates of serious illness and death are highest among persons age >65 years, children <2 years, and persons of any age who have medical conditions that place them at increased risk for complications from influenza.

Figure One

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Health care providers can reduce illness and death form influenza and pneumonia by getting immunized themselves, by providing flu vaccine to their patients, and by giving pneumococcal vaccine to those at risk, especially those 65 years and older.

Clinical Signs and Symptoms of Influenza

Influenza viruses are spread from person to person primarily through large-particle respiratory droplet transmission. Transmission via large-particle droplets requires close contact between source and recipient persons because droplets do not remain suspended in the air and generally travel only a short distance (≤1 meter) through the air. Contact with respiratory-droplet contaminated surfaces is another possible source of transmission.

The typical incubation period for influenza is 1-4 days (average: 2 days). Adults can be infectious from the day before symptoms begin through approximately 5 days after illness onset. Young children also might shed virus several days before illness onset, and children can be infectious for ≥10 days after symptom onset. Severely immunocompromised persons can shed virus for weeks or months.

Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and respiratory signs and symptoms (e.g., fever, myalgia, headache, malaise, nonproductive cough, sore throat, and rhinitis). Among children, otitis media, nausea, and vomiting also are commonly reported with influenza illness. Uncomplicated influenza illness typically resolves after 3-7 days for the majority of persons, although cough and malaise can persist for >2 weeks. Influenza virus infections can cause primary influenza viral pneumonia; exacerbate underlying medical conditions (e.g., pulmonary or cardiac disease); lead to secondary bacterial pneumonia, sinusitis, or otitis; or contribute to coinfections with other viral or bacterial pathogens.

Hospitalizations and Deaths from Influenza

Influenza-related hospitalizations or deaths can result from the direct effects of influenza virus infection or from complications due to underlying cardiopulmonary conditions and other chronic diseases. Rates of influenza-associated hospitalization are higher among young children than among older children when influenza viruses are in circulation and are similar to rates for other groups considered at high risk for influenza-related complications, including persons aged ≥65 years. Hospitalization rates during influenza season are substantially increased for persons aged ≥65 years.

Influenza-associated deaths are uncommon among children but represent a substantial proportion of vaccine-preventable deaths. Surveillance conducted in the 2005-2006 influenza season by the New Jersey Department of Health and Senior Services (NJDHSS) identified 25 cases of severe or fatal pediatric influenza in New Jersey. (http://nj.gov/health/flu/professionals.shtml)

Vaccine Composition

Both live attenuated (i.e., procedure which makes the strain of the virus less virulent) influenza vaccine (LAIV) and inactivated vaccine (TIV) contain strains of influenza viruses that are antigenically equivalent to the annually recommended strains: one influenza A (H3N2) virus, one influenza A (H1N1) virus, and one influenza B virus. Each year, one or more virus strains might be changed on the basis of global surveillance for influenza viruses and the emergence and spread of new strains. Only the H1N1 strain was changed for the recommended vaccine for the 2007–08 influenza season, compared with the 2006–07 season. Viruses for both types of currently licensed vaccines are grown in eggs. Both vaccines are administered annually to provide optimal protection against influenza virus infection. Both TIV and LAIV are widely available in the United States. Although both types of vaccines are expected to be effective, the vaccines differ in several aspects.