By Aparna Mani, MD, PhD
MGH Medical Walk-In Unit

It seems like every year come winter we’re inundated with health care providers’ recommendations and public service campaigns to get the flu vaccine. But what exactly is the flu and why is it such a big deal? ‘Flu’ is short for influenza, an infectious disease caused by a small group of viruses – namely influenza virus A, influenza virus B and influenza virus C. These viruses target and infect the respiratory tract (nose, throat and lungs) causing the illness we call the flu. People with the flu experience a combination of high fever, chills, sore throat, significant fatigue, muscle aches, headache, and cough. True, many of these same symptoms are associated with the common cold, but colds are caused by a different set of viruses and these symptoms are much less severe (and much shorter in duration) than with the flu.

One reason there is so much public attention given to the flu is its potential to cause large-scale outbreaks. In fact in 1918 a particularly lethal flu pandemic spread through many parts of the world, resulting in an estimated 500 million deaths. Though we have not seen as high a fatality rate from the flu in recent memory, and even though most healthy individuals will completely recover from the flu in about one to two weeks, it’s still a highly contagious illness that has the potential to turn particularly severe (and potentially deadly) in certain populations. The CDC estimates that approximately 3,000 to 49, 000 people have died from the flu each year over the past 30 years. This is the driving force behind the recommendation for the flu vaccine.

The Flu Vaccine

Each year the World Health Organization researches and identifies the strains of influenza viruses they predict will cause the bulk of the flu illness for the upcoming season.  Based on these predictions vaccine manufacturers develop the seasonal flu vaccine, which is made available to the public starting in the fall.  Why does a brand new vaccine need to be developed each year? The influenza viruses, influenza A in particular, have a high rate of mutation. This means that they’re able to change a component of themselves, one of their viral “body parts” as it were, to such a degree that the immune system is unable to remember prior versions of the virus. Put another way, someone who had the flu last year may build up immune defenses against the strain of virus that caused their illness, but those defenses may not recognize a new or different version of the virus this year. Thus, the flu vaccine given this season is no longer protective for the next.  This is also why some individuals may still get the flu despite having gotten a flu shot:  they may have gotten infected with a strain of the virus that was not included in the vaccine.  There are two forms of influenza vaccine available: an injectable version commonly known as the “flu shot” and a nasal vaccine which is sprayed into the nose.  You cannot get the flu illness from either of these vaccines themselves. The virus used to make the injectable vaccine is inactivated or killed while the virus used to make the nasal version is attenuated or weakened.

Potential Complications, Treatment and Prevention

So how does a virus that causes sore throat, muscle ache, fever, chills, headache and cough become deadly? Well, some individuals can develop an infection of the lung or pneumonia caused by the influenza virus itself, or by bacteria that began growing in the lungs while the immune system was busy dealing with the flu virus.  Babies under the age of 2, pregnant women, and people over 65 are most susceptible to this complication.  People who are immunocompromised (have a weakened or no immune system) from another illness, who smoke, or have a chronic illness such as asthma, diabetes, lung or heart disease are also at risk for severe complications.

What happens when someone gets the flu?  Depending on the severity of symptoms and any complicating medical conditions, healthcare providers may prescribe an oral antiviral medication. Though these medications do not cure the flu, they may decrease the severity and duration of symptoms as well as the chance of developing complications.  The CDC recommends such treatment for specific populations, including hospitalized patients and people at high risk for complications including children under 2; adults over 65; pregnant or postpartum women; residents of nursing homes; immunosuppressed individuals; and those with chronic illnesses.  For anyone not included in the above populations, flu symptoms can be effectively treated with some over the counter medications. Acetaminophen or ibuprofen can help to reduce fever, headache and muscle aches.  Aspirin or other salicylates should be avoided, especially in children under 18, as it has been associated with Reye syndrome. In addition, people with the flu should drink plenty of fluids and get a good amount of rest. Flu symptoms may last for one week or more.

As with anything, prevention is the best course of action.  Flu viruses are highly contagious through contact with contaminated surfaces and through the air, so habits such as hand washing with soap and water, covering one’s mouth when coughing or sneezing, and avoiding touching the eyes, nose and mouth limit its spread and transmission.  Good hygiene and annual vaccination are the best defenses against the flu.