The Flu Vaccine, Explained

Osmosis Team
Published on Dec 12, 2019. Updated on Dec 7, 2020.

It's flu season! Here's a quick primer from Osmosis on all things related to the flu season: what influenza is and how it spreads, and why you should get vaccinated if you haven't already. 

What is the flu?

Influenza, or simply the flu, is caused by the influenza virus. Almost everyone has had it. You’re probably familiar with the symptoms: high fever, runny nose, sore throat, muscle pains, headaches, coughing, sneezing, and feeling tired. It’s…terrible. The CDC Foundation reports that on average each year 5–20% of the US population gets the flu. 

The good news is that the flu doesn’t last long. It usually improves within a week. In rare cases, people can become seriously ill, requiring hospitalization and care in the ICU.

Osmosis illustration of the symptoms of influenza.

How does the flu spread?

The flu spreads when a sick person sneezes or coughs. This sends thousands of virus-containing droplets into the surrounding area. These viruses might land directly on another person’s nose or mouth. More commonly, the viruses end up landing on nearby objects.

The flu virus is very hearty and can survive for hours in the environment. To make matters worse, a person may be contagious a day before symptoms even begin and up to two weeks after symptoms have ceased. 

So, while it’s great that Debbie is back to work this week after recovering from the flu, it’s not so great that the donuts she brought to share are contaminated with that same flu virus. Thanks, but no thanks, Debbie!

Osmosis illustration of Debbie serving some flu-contaminated donuts to her colleague. 

How do you prevent the flu?

If you don’t want to feel like garbage, or get your friends, family, and coworkers sick, what can you do? The most effective way to prevent influenza is through vaccination, which can be done by injection or nasal spray.

These vaccinations usually contain three variations of weakened or inactivated influenza virus strains that are predicted to dominate for a specific season. Because flu viruses mutate rapidly, these vaccines are updated twice a year. For a few other best practices, Medical News Today suggests practicing some good health habits.

Is the flu vaccine effective?

How well do these vaccinations work? The success rate depends on a couple factors. First, high-risk individuals, like pregnant women, those with a chronic health condition, infants under six months, or people over sixty-five years of age, are more susceptible to the flu despite being vaccinated. Second, since the vaccine is based on predictions, some years are better than others. 

On average, the flu vaccine reduces the risk of illness by roughly half. The likelihood of getting sick over the entire flu season decreases from about 10% to 5%. Without the vaccine, the average person may get the flu about one out of every ten years, and with the vaccine one out of every twenty years.

Should I get the flu vaccine? 

If your risk of getting the flu is already quite low, why should you get the vaccine? For one thing, it’s important to remember that the flu can do more than make you feel terrible. The flu can cause serious injury—even death!

In the 2018–19 flu season in the United States, the CDC estimates that the flu vaccine prevented 4.4 million illnesses, 58,000 hospitalizations, and 3,500 deaths associated with flu.

Getting the flu vaccination also decreases your chances of passing the flu on to someone else. The more people in a community that are vaccinated against the flu, the fewer people there are who will contract and spread the flu. And, in effect, the more uncontaminated donuts you can eat. Thanks, Debbie!

Getting vaccinated helps you protect those who can’t get vaccinated, like infants, people with chronic illnesses, and individuals over the age of 65. We refer to this as herd immunity. The herd is protecting the most vulnerable groups.Osmosis illustration showing which population groups are more susceptible to flu complications.

When should I get vaccinated? 

A yearly flu vaccine is recommended for everyone over six months old, with a few exceptions. It’s not recommended for people with life-threatening egg allergies or a history of Guillain–Barré syndrome.

Otherwise, since flu season begins in the fall and peaks in the winter, it’s a good idea to get vaccinated by the end of October if you live in the Northern Hemisphere. That said, the vaccine still provides protection if you get it later in the season. It’s more important than ever to get vaccinated for the flu this year due to COVID-19 since it is possible to be infected with both at the same time. 

How can I tell COVID-19 and the flu symptoms apart?

Unfortunately, due to many similarities, it is difficult to tell the flu and COVID-19 apart only based on symptoms, besides the loss of taste and smell associated with COVID. The only definitive way to know the cause of the symptoms is by getting tested for either virus. This season the CDC has developed a test to check for A and B type seasonal flu viruses and SARS CoV-2.

Alright, as a quick recap…

The flu is caused by the influenza virus, a hearty virus that can live in the environment for hours. Its symptoms (sneezing, coughing, muscle pains) usually only last a week or so, but in some cases can lead to serious illness and hospitalization. The most effective way to prevent the spread of the virus is through vaccination. Even if your chances of getting the flu are low, getting the vaccination will help you protect the most vulnerable in your community. You should aim to get vaccinated by the end of October, but a vaccination later in the season can still be effective. Remember to only leave your home for essential reasons to reduce the risk of spreading the flu during the COVID-19 pandemic and flu season. 


Learn more about vaccinations and other important clerkships topics with Clinical practice videos on Osmosis Prime.