The Flu and Your Health

Reading time: 5 – 8 minutes

It’s the gift-giving season. However, there’s one gift this time of year you don’t want to give or get: the flu virus. Flu season runs from November to April, with most cases occurring between late December and early March. About 10-20% of people get the flu every winter [1]. In children, the number is even higher with up to 40% of children becoming clinically ill due to the influenza virus.

What is influenza?

Influenza is a respiratory infection caused by a number of airborne RNA viruses that enter the body through the nose or mouth. Influenza viruses bind to epithelial cells in the nose, throat and lungs. Cells than absorb the virus. Once inside, the virus replicates using a cellular enzyme called an RNA-dependent RNA polymerase. The polymerase enzyme lacks proofreading capability and makes a spontaneous mutation at a rate of 1 per genome per replication [2]. Thus, essentially every influenza virus replicated contains a mutation. This is the reason why influenza viruses continually change over time and are able to evade the host immune system.

Symptoms of the flu present quickly and are worse than the common cold. Flu symptoms include body or muscle aches, chills, cough, high fever lasting 3-4 days, headache, sore throat, stuffy nose, extreme tiredness and stomach symptoms (more common in children), including nausea, vomiting and diarrhea. The incubation period between acquiring the infection and becoming ill is 1-4 days. Most heathy adults are able to infect other people 1 day before symptoms develop and up to 5 days after becoming sick [3]. Viral shedding, the period during which a person can infect others, usually peaks on the second day of symptoms. Children can infect others for several days prior to developing symptoms and can be infectious for more than 10 days. Since children can shed the greatest amounts of virus, they pose the greatest risk for viral transmission.

The flu vaccine: your options

The best way to prevent seasonal flu is to get vaccinated. Hospitalization and death from flu complications pose real risks; every year, on average, more than 200,000 people are hospitalized from flu complications and approximately 36,000 people die from the flu [3]. Immunizing children against influenza is perhaps the best method to reduce the occurrence of the flu in the community. If children receive the flu shot but the rest of the family abstains, the influenza attack rate drops by 40%; if parents also get the flu shot, the influenza attack rate drops by 80% [4].

The flu vaccine is available in two forms, a shot and a nasal spray (FluMist). The flu shot, which is approved for use in children 6 months and older, contains an inactivated flu virus. Although you may develop a slight reaction to the shot, including soreness at the injection site, muscle ache or fever, you won’t get the flu because the viruses in the vaccine have been inactivated. The nasal spray flu vaccine (FluMist), which is approved for use in children 2 years and older, contains a low dose of live but weakened flu virus. Similar to the flu shot, the nasal spray doesn’t cause the flu, but prompts an immune response so that your body develops antibodies necessary to fight influenza infection. A review of 48 reports on influenza vaccine efficacy over the past four decades found that the flu shot was 80% efficacious against influenza in healthy adults when the vaccine matched the circulating strain and the circulation was high [5]. If the circulating strain didn’t match the vaccine, efficacy was reduced to 50%. The flu vaccine was 30% effective against influenza-like illness. FluMist efficacy has been reported to be higher in both children and adults [6-8].

What else can you do?

In addition to the flu vaccine, one of the best ways to avoid getting sick and stay healthy is to simply wash your hands. Even something as simple as coughing or sneezing can spread cold and flu germs; hand washing is the single most important thing you can do to prevent the spread of infection and to stay healthy. Some scientists estimate that as much as 80% of all infections are transmitted by unwashed hands [9]. Nevertheless, a dab of soap and a quick rinse isn’t effective. The key is to wash your hands for at least 20 seconds to ensure that you’ve removed the microbes (here’s a trick: sing the ABC’s to yourself). By rubbing your hands with soapy water, you pull dirt and oil from your skin. The soap lather suspends any germs trapped inside and are then washed away when rinsing. If soap and water aren’t available, use an alcohol-based hand sanitizer. However, while alcohol-based hand sanitizers reduce the number of germs on skin, they aren’t necessarily more effective at reducing the flu virus on human hands. Studies have found that hand washing with soap and water is superior to all alcohol-based treatments.

References

1. Evans M. Flu shot. Can Fam Physician. 2005 Nov;51:1511-2, 1515-6.
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2. Drake JW. Rates of spontaneous mutation among RNA viruses. Proc Natl Acad Sci U S A. 1993 May 1;90(9):4171-5.
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3. Key Facts About Seasonal Influenza (Flu). Centers for Disease Control and Prevention. Updated 2007, Sep 17.
4. Hurwitz et al. Effectiveness of influenza vaccination of day care children in reducing influenza-related morbidity among household contacts. JAMA. 2000 Oct 4;284(13):1677-82.
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5. Jefferson et al. Vaccines for preventing influenza in healthy adults. Cochrane Database Syst Rev. 2007 Apr 18;(2):CD001269.
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6. Belshe et al. The efficacy of live attenuated, cold-adapted, trivalent, intranasal influenzavirus vaccine in children. N Engl J Med. 1998 May 14;338(20):1405-12.
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7. Belshe et al. Efficacy of vaccination with live attenuated, cold-adapted, trivalent, intranasal influenza virus vaccine against a variant (A/Sydney) not contained in the vaccine. J Pediatr. 2000 Feb;136(2):168-75.
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8. Treanor et al. Evaluation of trivalent, live, cold-adapted (CAIV-T) and inactivated (TIV) influenza vaccines in prevention of virus infection and illness following challenge of adults with wild-type influenza A (H1N1), A (H3N2), and B viruses. Vaccine. 1999 Dec 10;18(9-10):899-906.
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9. Put Your Hands Together. National Center for Preparedness, Detection, and Control of Infectious Diseases (NCPDCID) and National Center for Zoonotic, Vector-Borne, and Enteric Diseases (NCZVED). 2008 Oct 13.