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  • Writer's pictureAlan Frischer, MD, MPH

Influenza (Flu)

Updated: Sep 26, 2021

Here we go again: We are entering the flu season. What will it be like this year, and why is getting vaccinated so important?

Influenza (flu) is a contagious respiratory illness caused by a virus. It infects the nose, throat, and sometimes lungs, and can be mild, severe, or even deadly. Symptoms include fever, cough, sore throat, runny nose, body aches, headaches, chills, fatigue, and sometimes diarrhea and vomiting. It is communicated through tiny droplets that spread when we cough, sneeze or even just talk. They may land in the mouth or nose of people nearby, or we can infect ourselves when we touch an object that has the flu virus on it, and then touch our own nose, mouth or eyes.

It’s important to note that we are at our most contagious during the first three to four days of the illness, but flu symptoms don’t even appear until about two days after exposure. So, it’s very easy to spread the virus to friends, loved ones, and strangers before we even know that we have it!

Which flu viruses will we see this season? There are many different ones and they are constantly changing. About a year ago, scientists used worldwide patterns to forecast which strains we are most likely to see now. Usually, they choose the three most likely strains, but this year the vaccine is quadrivalent – it protects against the four most likely viruses. This increases the odds of hitting the correct strains. The current flu vaccine is an injection made up of killed viruses from those four lines. There is also a lesser-used nasal spray flu vaccine made of live attenuated flu viruses. This means that the actual viruses are living but weakened, so less likely to cause disease. Your doctor can advise you as to which vaccine is best for you.

The time to get a flu vaccine is before the flu begins to spread. It takes about two weeks after receiving the vaccine for our bodies to develop protective antibodies. So, NOW is the time.

How severe will this season be? It’s too soon to predict. Flu season runs from about October to May nationwide, but here in California we tend to lag behind the rest of the country. But we can expect that it will affect between 9 and 49 million people across the nation this year.

How can we each avoid coming down with the flu? Getting vaccinated every year is a great way, and it’s quite safe for almost everyone. (Don’t skip a year, because the viruses that come around each year are usually different from the previous year’s. Also note that the immunity you may have from either getting the flu or from getting a vaccine declines over time.) Avoid public places where you might come into contact with a lot of sick people – including those whose symptoms aren’t yet showing. Wash your hands frequently, and keep them away from your face. Maintain a healthy lifestyle including proper sleep, exercise and nutrition. If you are sick, stay home to prevent spreading your germs to others.

And yes, there are those who get the flu despite having been vaccinated. How can this happen?

  • You might be exposed to the flu virus shortly before or after getting the flu vaccine. Because it takes two weeks for the antibodies to fully develop, it may simply be a matter of timing.

  • You might be exposed to a flu virus that is not included in the vaccine, as there are many different strains that circulate each year. Scientists are quite good at choosing the most likely strains, but it’s really a best guess.

  • While the vaccine works for the vast majority of us, its effectiveness may be reduced by age, chronic disease, or other factors.

Are flu vaccines safe? Hundreds of millions of Americans have safely received flu vaccines over the past 50 years, and extensive research is done to support our safety. You cannot get the flu from the vaccine injection. There are, however, potential side effects from the vaccine that occur roughly one or two percent of the time. These rare and mild side effects may last a day or two and include soreness or redness at the injection site, headache, fever, nausea and muscle aches. Interestingly, these potential side effects may resemble the flu itself – but are not the flu. As is the case with all vaccines, there is an approximately one per million – let me repeat that: one per million - chance of developing Guillain-Barre syndrome.

What if you do come down with the flu? Medicines like Tamiflu can help reduce the symptoms and length of infection, if started during the first few days. But overall, the flu vaccine works. Most insurers cover the vaccine because they are convinced of this, and as a result, that it benefits their own bottom-line. The vaccine protects us each from illness, but it’s also for the greater good: when we choose to become vaccinated it reduces the spread of the disease in the community.

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