The coming flu season

Oct. 1, 2007
Each year in the United States, on average, 5 to 20 percent of the population gets the flu.

by Charles John Palenik

Each year in the United States, on average, 5 to 20 percent of the population gets the flu. More than 250,000 people require hospitalization while about 36,000 die. The flu season usually runs from November through March. Some years, cases continue into April and May. For the last 25 years, the heaviest flu activity has occurred in February.

Influenza viruses can cause disease among people of any age, but rates of infection are highest among children. Serious illness and death are highest among persons ages 65 or older, and children ages 2 and younger. People of any age with certain medical conditions (e.g., congestive heart failure, asthma, diabetes), or who live in some type of long-term care facility are at increased risk for serious complications.

Vaccination is the most effective method for preventing influenza virus infection. The focus of influenza immunization efforts is primarily toward providing vaccination to people at risk for influenza complications and to those who come in contact with these people. The greatest reduction in influenza will occur only if everyone is vaccinated.

There are two types of influenza vaccine. The trivalent inactivated (killed) influenza vaccine, or TIV, may be used on any person age 6 months or older. This flu shot involves an injection into muscle, usually in the upper arm. The other is a live, attenuated (weakened) influenza vaccine, or LAIV, which is sprayed into the nostrils.

For most people, vaccination will prevent serious influenza-related illness. Vaccination will not prevent “flu-like” illnesses caused by other viruses. It takes two weeks for protection to develop after vaccination. So, vaccine that is given early in the flu season will provide a longer period of protection. Influenza vaccines can reduce infection in 70 to 90 percent of healthy adults under the age of 65.

Any people older than six months of age, including healthy people and those with chronic conditions, can receive the TIV. A special recommendation goes to anyone who lives with or cares for people at high-risk for influenza-related complications, including health-care workers. Some people should consult with their primary health-care provider before vaccination. This includes anyone with allergies to eggs or a history of Guillain-Barré syndrome. Anyone moderately to severely ill should wait until they recover to be vaccinated.

In 2003, the FDA approved the LAIV (FluMist) for U.S. use. Administration of LAIV is by an intranasal route. It contains the same three viruses as the TIV. When sprayed into the nose, the viruses stimulate an immune response. LAIV is for healthy people ages two to 49 who are not pregnant.

People who should not get the LAIV include those age 50 or older and those under six months, people with long-term health problems (heart, lung, kidney, asthma, and metabolic diseases), pregnant women, and those with a history of Guillain-Barré syndrome. Those with serious allergies to eggs should discuss LAIV immunization with their primary health-care provider. Those moderately or severely ill should postpone vaccination until they recover.

Because influenza viruses undergo frequent antigenic change (e.g., antigenic drift or shift), the annual vaccine contains influenza viruses believed to be circulating during the coming flu season. The 2007-08 trivalent vaccine strains are A/Solomon Islands/3/2006 (H1N1)-like (new for this season), A/Wisconsin/67/2005 (H3N2)-like, and B/Malaysia/2506/2004-like viruses. Generally, an “educated guess” proves correct; however, widespread circulation of a new, highly infectious influenza virus could result in an epidemic.

It is recommended that health-care workers receive an annual influenza vaccination. This is a high priority for reducing morbidity associated with influenza in health-care settings and expanding influenza vaccine use. National survey data indicate that only 42 percent of health-care workers receive the vaccine each year. Vaccination of health-care workers has been associated with reduced work absenteeism and fewer deaths among nursing home patients and elderly hospitalized patients.

Factors associated with a higher rate of influenza vaccination among health-care workers include older age, being a hospital employee, having employer-provided health-care insurance, having had a pneumococcal or hepatitis B vaccination in the past, or having visited a health-care professional during the previous year.

Some health-care facilities offer free TIV to their employees. Some even offer it to employees’ families. Employees with influenza usually stay home to recuperate and not spread the infection. When a family member becomes ill, there is a chance that the employee also will stay home. Offering the vaccine to the entire family can reduce absenteeism.

Dr. Charles John Palenik is the director of Infection Control Research and Services at the Indiana University School of Dentistry. He is the co-author of the popular “Infection Control and Management of Hazardous Materials for the Dental Team.” In 2003, he was chairman of the Executive Board of OSAP, dentistry’s resource for infection control and safety. Questions about any infection control issue may be directed to [email protected].

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