October 2000

Important News About the Flu and Its Vaccine

Peter P. Greaney , M.D .
Board-Certified Occupational Medicine Physician

An Invincible, Evolving Virus

Originating from distant corners of the world—from places like Tunisia, Albania and China—the influenza virus will soon arrive on the doorsteps of the United States, bringing on the 2000-2001 flu season that runs from November to March. And for public health officials, preparing for this year's flu may be more challenging than last year due to delays in the distribution of vaccine supplies.

The influenza virus has been one of the most invincible diseases mankind has faced. Its ability to survive, despite tremendous advances in modern medicine, is based on its unique characteristics that allow it to change.

The physical structure of the virus makes it particularly prone to small surface changes in antigens during replication. These changes allow the virus to evade the host's immune system. A minor change in surface antigens of a virus may cause an epidemic because most people do not have enough antibody protection from past exposure to similar viruses. A major change in the virus' surface antigens may cause a pandemic, if the virus is easily transmitted from person to person. The evolving nature of the virus thus makes it necessary for people to be revaccinated each year with the most prevalent flu strains.

Global Surveillance Resources Used in Identifying Influenza Strains

Every year, the influenza vaccine must be updated to match the flu strains that are likely to be the predominant type in the upcoming flu season.

The United States Public Health Service (USPHS) must identify and select these specific strains, based on data from the World Health Organization (WHO), the U.S. Centers for Disease Control and Prevention (CDC), the Federal Drug Administration (FDA) and the National Institutes of Health (NIH).

If the strains used to create the vaccine are a good match with the virus causing the illness, the vaccine can be particularly effective in preventing the onset of the flu or minimizing its symptoms. Likewise, an influenza vaccine can be less effective with a poor match.

Selecting the “right” strains for vaccine purposes requires a thorough analysis by public health professionals. To accomplish this, an international network for influenza surveillance has been established to collect worldwide data about circulating strains of viruses and statistics on influenza outbreaks. WHO operates this network and has 110 national influenza centers in 82 countries to monitor flu activity in all regions of the world. WHO has also created FluNet , a web-based data resource, which is used by the centers to store and analyze data on influenza activity, which is categorized by location, severity of outbreaks and type and number of influenza specimens.

Impact of Influenza in U.S. and Worldwide

Despite these global resources, the influenza virus continues to cause considerable morbidity and mortality each year. New strains of influenza, for which people have no immunity, appear periodically, at irregular intervals, causing worldwide pandemics. The first documented pandemic occurred in 1580. Since then, there have been 30 documented pandemics, including the Spanish Flu in 1918-1919, which was particularly virulent, killing about 40 million people. The CDC estimates about 76 million people are at high risk for complications from the flu, yet only half of this group receives the vaccine.

It is estimated that in the United States about 20,000 people die each year from the flu and another 110,000 are hospitalized for flu complications, including pneumonia.

Two New Strains Included in This Year's Vaccine

This year, the influenza vaccine in the United States will contain three different inactivated flu strains. The vaccine will contain two new A strains: A/Panama and A/New Caledonia. The third strain is B/Yamanashi, which is unchanged from last year's flu vaccine.

According to the CDC, the introduction of new vaccine strains has, in the past, affected vaccine production. Occasionally, manufacturers experience processing problems with new strains, as well as lower than expected growth rates. The A/Panama strain was identified in late April to be included in the 2000-2001 vaccine, and manufacturers have reported problems in generating sufficient quantities of the strain for the upcoming flu season.

Impact on Delay of Vaccine Supply

The delay of distribution of the vaccine is causing public health officials to encourage providers to take specific steps to ensure that high-risk individuals, who choose to be vaccinated, receive the vaccine.

A report by the U.S. Advisory Committee on Immunization Practices (ACIP) issued the following statement: “As vaccine first becomes available, efforts should be focused upon persons at high risk of complications associated with influenza disease and on healthcare workers.”

According to ACIP, vaccination efforts focused on high-risk groups should continue into December and later. The agency identified those at high risk as:

Persons 65 years of age or older
Residents of nursing homes and those people in chronic-care facilities with chronic medical conditions
Adults and children (6 months or older) who have chronic pulmonary or cardiovascular disease, including asthma or who have been hospitalized or received medical attention within the last year for diabetes mellitus, kidney dysfunction, blood disorders, or immune system problems
Children and teenagers (six months to 18 years) who are receiving long-term aspirin therapy
Women who are in their second or third trimester of pregnancy during the influenza season

In addition, the agency and CDC recommend the vaccine for healthcare workers, persons 50-64 years of age and family members of high-risk individuals. The CDC has indicated that there are about 75 million doses of the vaccine, which is expected to meet this year's demand. The CDC has also recommended delaying mass vaccination campaigns until later in the season in order to minimize cancellations of vaccine campaigns and wastage of vaccine doses caused by delays in vaccine delivery.

Although supplies of the vaccine are expected to be sufficient, those in the healthcare community should make extra efforts to reach those individuals whose exposure to the flu may cause severe health complications.

Healthy people should not be turned away, yet specific action must be taken to reach people in the high-risk group. Consideration should be given to reaching high-risk individuals through targeted print and media announcements.

Cost Benefit Analysis of Vaccine

A study published in the Journal of the American Medical Association indirectly supports the CDC's recommendations to focus vaccinations on high-risk individuals by stating that influenza vaccines for healthy working adults, who are younger than 65, may not routinely result in societal economic benefit. In the study, influenza vaccines or placebos were given to participants in the 1997-1998 and 1998-1999 flu seasons.

In the 1997-1998 flu season , the vaccine virus was not one of the predominant circulating viruses, and vaccination did not reduce the incidence of influenza-like illness, number of physician visits or lost work days. The net societal cost was $65.59 per person, which included direct costs for physician visits, prescription, and the cost of the vaccine, as well as indirect costs, such as lost work time.

In contrast, the vaccine given during the 1998-1999 flu season was well matched, and those who received the vaccine reported “34% fewer influenza-like illnesses, 42% fewer physician visits and 32% fewer lost workdays” than those in the placebo group. However, vaccination was still associated with a net societal loss related to influenza-like illnesses of $11.17 per person.

The authors of the study do not dispute the health benefits derived from the influenza vaccine. When the vaccine and circulating virus are well matched, the vaccine can reduce the rates of influenza-like illness, lost workdays and physician visits in healthy working adults. However, the report did underscore that cost per illness is much lower in healthy adults versus the elderly and vaccination may not provide overall economic benefit in most years.

Those behind the study at the CDC suggested that the results could be used to help set societal priorities when vaccine is in short supply.

Considerations before taking the Vaccine & Side Effects of the Vaccine

Before taking the vaccine, it's important to tell your healthcare professional if you have ever had any unusual or allergic reaction to influenza vaccine or to antibiotics, such as gentamicin , streptomycin or other aminoglycosides . Tell your healthcare professional if you are allergic to any other substances, especially eggs.

There is another known reaction to the vaccine called Guillain-Barre Syndrome (GBS). This disease is a rare disorder affecting the nervous system, which results in paralysis. Recovery is complete or nearly complete in 85% of the cases. An average of 6% of persons with GBS will die. The cause of GBS is unknown and about 10-20 cases per one million adults occur in the United States each year.

Since the virus is inactivated, it cannot cause influenza. The most common side effect is tenderness, redness or a hard lump at the place of injection. Less common side effects include fever, general feeling of discomfort or aches and pain in muscle.

Prevention and Treatment of the Flu

The influenza vaccine is the optimum method in preventing and reducing the severity of the flu. However, a common sense approach in practicing good hygiene may also prevent exposure to the influenza virus. The virus is likely transmitted through small droplets. Washing your hands and observing good hygiene habits may reduce the risk of exposure.

If you do get the virus, you may want to talk to your doctor about using an antiviral drug. There are two types of medication, Relenza ( GlaxcoWellcome ) and Tamiflu (Roche). Both can reduce the severity and duration of flu infections from A and B strains—if taken within 48 hours of symptom onset. Also, it's advisable to stay indoors and out of public places to prevent the spread of the virus.

Outlook on Flu Season

The vaccine supply situation still remains fluid. Health officials from the CDC and ACIP have announced that they may modify recommendations for the 2000-2001 influenza season if a supply shortfall emerges. New and updated information will be released from the CDC and FDA throughout the course of the flu season to keep public health officials appraised of the situation.

References

The following sources provided references for this article:

http://www.who.int/emc/diseases/flu/

http://www.cdc.gov/od/oc/media/pressrel/r2k0928.htm