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Influenza epidemics occur every year in the United States, typically beginning in the late fall or winter and concluding during the spring.1
During the 2006–2007 season, influenza circulated at epidemic levels for about 14 weeks and peaked during February, the month most frequently associated with peak activity over the past 31 influenza seasons.1,2
According to estimates from the Centers for Disease Control and Prevention (CDC), influenza has caused roughly 36,000 deaths and 226,000 hospitalizations annually.3,4
However, the rate of flu varies each year based on viral virulence and duration of circulation. Complications, hospitalizations, and death are most common in patients aged ≥65 years.5,6
In recent years, there has been a growing recognition among oncologists and other cancer care professionals of the importance of vaccination against influenza in patients with cancer.
For most people with cancer, vaccination for influenza is not only safe, but also a crucial part of staying as healthy as possible. Owing to their weakened immune system, patients with cancer are at high risk for infection with flu and pneumonia viruses, which can be lethal in these individuals. Yearly flu and pneumonia shots often prevent infection entirely and can lessen the severity of illness in those who do get sick.Influenza Viruses
Influenza viruses are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates for hospitalization and death. Influenza type C differs from types A and B in some important ways. Type C infection usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have the severe public health impact that influenza types A and B do. Efforts to control the impact of influenza are aimed at types A and B.
Influenza type A viruses are divided into subtypes based on differences in two viral proteins called the hemagglutinin (H) and the neuraminidase (N). The current subtypes of influenza A are designated A(H1N1) and A(H3N2). Influenza A(H1N1), A(H3N2), and influenza B strains are included in each year’s influenza vaccine. In the years since its emergence, type A(H3N2) epidemics have caused more than 400,000 deaths in the United States alone, and more than 90% of these deaths have occurred among people age 65 and older.
Influenza type A viruses undergo two kinds of changes. One is a series of mutations that occur over time and cause a gradual change in the virus. This is called antigenic “drift.” This constant changing enables the virus to evade the immune system of its host, so that people are susceptible to influenza virus infection throughout life. This process works as follows: A person infected with influenza virus develops antibody against that virus; as the virus changes, the “older” antibody no longer recognizes the “newer” virus, and reinfection can occur The older antibody can, however, provide partial protection against re-infection.
The other kind of change is an abrupt change in the hemagglutinin and/or the neuraminidase proteins. This is called antigenic “shift.” In this case, a new subtype of the virus suddenly emerges. Type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift.CDC Recommendations For Influenza Vaccination
Influenza vaccination is the most effective method for preventing influenza virus infection and its complications, which may be severe. The CDC updated its recommendations regarding who should receive influenza vaccination in 2008.1,7
Current recommendations regarding annual vaccination in children/adolescents and adults are summarized in Table 1 and Table 2, respectively. It is important to note that patients with cancer may fall into several of the categories shown in the tables.
In 2008, the Advisory Committee on Immunization Practices (ACIP) of the CDC expanded its recommendations for influenza vaccination for school-aged children.1,7
The ACIP-CDC now recommends that all children aged six months to 18 years receive annual influenza vaccination, beginning in 2008 if feasible, but beginning no later than during the 2009–2010 influenza season.1,7
Since influenza viruses undergo frequent antigenic change, persons recommended for vaccination must receive an annual vaccination against the viruses known to be in circulation each year.
According to the CDC,1
trivalent influenza vaccine may be used for any person aged ≥6 months, including those with high-risk conditions. The 2008–2009 trivalent vaccine virus strains are A/Brisbane/59/2007 (H1N1)-like, A/Brisbane/10/2007 (H3N2)-like, and B/Florida/4/2006-like antigens.1
Live, attenuated-virus vaccine is currently approved only for healthy, nonpregnant persons aged 5–49 years.
Table 1. Influenza Vaccination Recommendations, 2008:
Children and Adolescents Aged Six months to 18 years*+