Just the Flu? What You Need to Know About This Deadly Illness

By Dr. Guy SooHoo

“It’s just the flu.” is a frequently uttered diagnosis from both healthcare providers and the general public. While the meaning is immediately clear to all, these few words often mask what can be a devastating illness with life-threatening and deadly implications. Most people consider an influenzal illness a moderate inconvenience, an illness that is a little worse than the “common cold” resolving after a few days of self-treatment with over the counter medications. Hence is the connotation suggested by “just the flu”. However, for others, influenza can be a deadly illness and continues to be a common cause of hospitalizations and death.

How deadly is influenza?
Few realize the devastation of the last great influenza epidemic in the winter of 1918 (1). It is estimated that between 20 – 50 million people died in that epidemic. More people died in that epidemic than from the “Black Plague” (Middle ages). More people died from influenza than were killed in World War I, and the most unusual part of that 1918 epidemic was its affliction of the young adult, as opposed to its more common victims who are the very young, elderly and those with severe medical co-morbidities such as underlying heart or lung disease.

How many people get influenza now?
Fortunately, influenza has not recurred with the same intensity and devastation as 1918, but there has always been concern for the potential of another great epidemic. It is estimated that between 5 – 20% of the general population with become infected with influenza each year. This translates to an estimated 226,000 hospitalizations and 36,000 deaths attributed to influenza each year. While there are some medications which can provide some modest relief from influenza, immunization remains the most important approach to minimizing the effects of influenza.

What is influenza?
Influenza is a respiratory virus which is spread from person to person through large particle respiratory aerosols or droplets often generated with a cough or sneeze. Infection can also occur after contact with respiratory-droplet contaminated surfaces (hard, non-porous surfaces, cloth, paper, tissue, hands). It is characterized by the sudden onset of fever, headache, sore throat, cough, coryza (runny nose), myalgias (muscle aching), and malaise. In children, nausea, vomiting and diarrhea are common symptoms. The illness can lead to worsening of underlying medical conditions (especially those with heart or lung disease), with subsequent development of viral pneumonia, bacterial pneumonia, otitis media, respiratory failure and ultimately death.

When are people contagious?
People are contagious BEFORE they exhibit symptoms. In adults, the virus is shed a day before onset of symptoms and persist for 5-10 days. In children, the virus is shed several days before they become ill and can persist for > 10 days. In patients who are immunocompromised, shedding of virus can occur for weeks to months. This means that during the peak of influenza season, anyone may be harboring the virus and people who are not obviously ill can be transmitting it to others. It has also become apparent that children play a large role in transmission of the virus, not only between themselves but then to their adult contacts which includes grandparents.

Who should get the influenza vaccine?
Based on the understanding of the transmission of influenza, recommendations from the Advisory Committee on Immunization Practices (ACIP) have expanded the influenza vaccination pool to include ALL children from ages 5 – 18 years (2). This will help prevent transmission among this group with the longest period of virus shedding, and also minimize transmission from this large pool to their adult contacts. There are already recommendations to vaccinate children from 6 – 59 months. In addition, vaccination is also recommended for all adults > 50 years of age, women who become pregnant during influenza season, patients with chronic pulmonary disorders (asthma, emphysema, COPD), cardiac disease, renal, liver, blood disorders and metabolic disorders including diabetes, chronic immunosuppression, any condition which may compromise respiratory function (such as cognitive dysfunction, spinal cord injuries, seizure disorders, neuromuscular disorders), nursing home residents or residents of chronic care facilities, health care workers, household contacts or caregivers of children < 5 or adults > 50, and household contacts and caregivers of any person with a high risk of complications from influenza (3). These recommendations cover a large group of people and relatively few people are excluded from this list. If there are any questions whether one falls into a group in which influenza vaccination is recommended, these questions can be referred to your personal physician or the Los Angeles County Immunization Program website at www.publichealth.lacounty.gov/ip

How effective is the influenza vaccine?
The most commonly administered vaccine is the trivalent inactivated influenza vaccine (TIV) and is based on the likely influenza strains circulating through the community (5). These strains are selected ahead of the influenza season and in most years provide protection in the 70-90% range. Even in the vaccine doesn’t prevent influenza, it also decreases the severity of the influenza infection. There is also a live, attenuated (weakened) influenza vaccine (LAIV) for those who want to avoid an injection for healthy persons between the ages of 2-49 years. However, there are restrictions on LAIV vaccination and these usually include those with underlying reactive airway disease (asthma). Always check on the most appropriate vaccine with your healthcare provider.

When should one get vaccinated?
The influenza vaccine is usually available each year in the early fall (late September/October). Vaccination should be done as soon as possible after the vaccine is available to prepare for the influenza season which usually peaks in the winter months of December and January. However, vaccination is the most important prevention against influenza and can still be effective if administered later in the influenza season (December or later).

What are side effects of influenza vaccination?
The vaccine may result in some local swelling, muscle soreness, fever and malaise. Not all vaccine recipients will experience these effects, but these are minor, self-limited and usually do not require more than local treatment or over the counter analgesics (acetaminophen or ibuprofen) for resolution. A common complaint is that the influenza vaccine causes the “flu”. This likely represents some of the mention local or mild systemic reactions. However, there are some who develop more severe reactions to the vaccine. These represent a small group of people who may not be able to be vaccinated with the influenza vaccine. Eggs are used in the production of the influenza vaccine (both TIV and LAIV), and thus those with egg allergies should NOT be vaccinated with the influenza vaccine. Those with previous hypersensitivity reactions or a rare side effect like Guillain-Barre syndrome to the influenza vaccine should also NOT be vaccinated with the influenza vaccine. If one is experiencing a febrile illness, vaccination should deferred until the illness has resolved.

Selected references

1. Taubenberger JK, Morens DM. 1918 influenza: the mother of all pandemics. Emerg Infect Dis 2006; 12: 15-22.
2. CDC. Seasonal Flu information for schools and childcare providers. Atlanta, GA. National Center for Immunization and Respiratory Diseases. CDC, 2007.
3. CDC. Prevention and Control of Influenza Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2008; MMWR 1-60.
4. http://www.cdc.gov/flu/school/index.htm
5. Website resource: http://www.cdc.gov/flu/