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14 answers to your questions about the flu and the flu shot

Flu season is already here – in fact, it’s the earliest start to the flu season in eight years. Have you gotten your flu shot yet?

As a physician working in internal medicine and infectious diseases at Sunnybrook, I’m often asked about the flu and the flu shot. Here are answers to some of the most commonly asked questions I hear:

1. What’s the difference between a cold and the flu? What are the symptoms of flu?

A simple cold and the flu are actually quite different. A person with a cold may have a cough, sneezing, runny nose, and feel unwell. A person with the flu may have those symptoms and can be sicker with symptoms such as high fever and full body muscle aches. Most people can generally still function when they have a cold. Flu symptoms can cause a person to feel unable to even get out of bed.

Flu causes over 3000 deaths every year in Canada and is the tenth-leading cause of death overall. The very young and old are at highest risk of complications, but bad outcomes in otherwise healthy people can happen too.

2. Can I get the flu from the flu shot? I got sick after my shot last year.

No, you can’t, because the flu shot contains dead virus. If you did get sick after getting the flu shot, there are a number of possible explanations:

  1. Maybe you had rhinovirus (common cold) and this was not flu;
  2. You were in contact with the flu before vaccination (it takes 2 weeks to develop full immunity); or
  3. Because the flu shot doesn’t provide 100 per cent immunity, you can still get the flu if you get the flu shot. But the shot doesn’t give you the flu.

3. Can I prevent the flu with holistic remedies (chicken soup, vitamins, infusers) instead of getting the flu shot? 

No. Hot liquids can soothe a sore throat and provide much needed fluids. But there is no evidence that chicken soup has any specific qualities that help prevent the flu. Your best protection against the flu is getting the flu shot, as there is lots of scientific evidence for this.

4. I heard there are a few different flu vaccines available this year. What are the differences? 

This year, there are trivalent and quadrivalent vaccines available. The trivalent vaccine contains three strains of flu virus and higher levels of an antigen, which helps the body produce a stronger immune response. This vaccine is recommended for people over age 65.

The quadrivalent vaccine contains the same as the trivalent, plus an additional strain (four strains total), but with a lower dose of antigen. This vaccine is given to people over 6 months old to 64 years.

5. I heard there’s weird stuff like formaldehyde and thimerosal/ethylmercury in the flu shot. Are those things safe to put in my body?

Formaldehyde occurs naturally in your body, and is a product of healthy digestive function. While it can be toxic and potentially lethal in high doses, it’s present in such small amounts in a flu vaccination that it is harmless.

Thimerosal acts as a preservative, keeping the flu vaccine free from contamination by bacteria and fungi. Thimerosal is made of an organic form of mercury known as ethylmercury, a safe compound that usually only stays in the blood for a few days.

This is different from the standard mercury that can cause illness in large doses, and from the mercury found in seafood (called methylmercury), which can stay in the body for years.

6. Is it possible to receive a preservative-free vaccine?

Preservatives are only used with multi-dose vials. If you would like to receive a preservative-free flu shot, check with a pharmacy or doctor’s office for the type they have available.

7. If the flu shot doesn’t guarantee 100 per cent immunity from the flu, why should I even bother getting it?  

If you get the flu shot, your risk of getting the flu or flu-related complications is between 40-70 per cent lower. The flu shot doesn’t give 100 per cent immunity because the flu virus mutates and changes as the year goes along. But when it comes to becoming infected with a potentially fatal infection, or transmitting that infection to those you love, 40-70 per cent lower risk is not something to dismiss.

At a population level, the flu vaccine campaign each year prevents thousands of hospitalizations for flu in Ontario alone. The more people get vaccinated, the better our “herd immunity,” which keeps our community safe. We all need to do our part to reduce the burden of flu every year.

8. Can you receive the flu shot if you’re feeling under the weather (cough, runny nose)?

If you have a mild cold, you may still receive a flu vaccination. Vaccination won’t be given if you have a serious, acute illness, such as anything with a fever or requiring antibiotics. Some people choose to wait until they are feeling “100%”; however, as we get in to colder weather and longer days, this may not happen and receiving the vaccination will keep being postponed.

9. Is it safe to get the flu shot while pregnant?

Yes, pregnant women should absolutely be getting the flu shot. In fact, the flu shot is recommended for pregnant women at all stages of pregnancy, as well as those who are breastfeeding. The flu itself, not the flu shot, can harm pregnant women seriously enough to land them in hospital and cause death. The flu poses a major threat to fetuses, too.

Another reason for pregnant women to get the shot: flu vaccination causes the body to produce infection-fighting antibodies. When a pregnant woman receives a flu shot, her antibodies get passed on to the developing fetus, providing protection to the newborn in the first months of life. A baby can also acquire antibodies through a vaccinated mother’s breast milk. This is particularly important since infants can’t receive the flu shot, and are at higher risk of complications if they do get the flu.

10. The flu doesn’t seem that bad. Why can’t I just take my chances and not get the shot?

You’re not only getting the flu shot for yourself, it’s offering protection to those around you.

While the flu may not seem like a big deal, it can have deadly consequences for many people. The flu can be a serious illness and cause hospitalizations and deaths, especially in people over 65 and young children like Jude, who was a healthy two-year-old when he died from Influenza B.

This year’s vaccine is quadrivalent, meaning it provides some immunity to four strains of the flu virus.

11. When someone gets the flu, how could it actually cause them to die?

The flu can be fatal for different reasons, including (but not limited to):

  • The flu can cause severe inflammation of vital organs, which is when the immune system attacks itself. This could leads to failure of vital organs and requires supportive treatment in the critical care unit
  • The flu can progress into a secondary bacterial pneumonia or other respiratory conditions, which could then become fatal
  • A person could have other medical conditions that can become unmanaged or more complicated when sick with the flu, such as exacerbation of lung disease, heart failure, kidney failure, or delirium. There is also evidence that flu can increase your risk of a heart attack, especially within the week after the infection 

12. Is my immunity lowered after the flu shot? Three years in a row, I got a cold right after the flu shot.

No, the flu shot does not lower your immune system – it boosts it.  You likely became ill with something else, but due to the timing it is common for people to think it was caused by the vaccine.

13. I live a healthy lifestyle (eat well, exercise, etc.) and consider myself to be a healthy person. I never get sick. Do I still need to get the flu shot?

Yes. You do. Public health agencies from around the world recommend everyone over the age of 6 months get the flu shot every year.

A flu shot not only protects you against the flu, it also helps protect your loved ones, colleagues, strangers on the street. By getting the shot, you are reducing your chance of spreading the illness. Even if you’re healthy, you should still get the flu shot.

14. I got the flu shot so that’s all I have to do to stop spreading the flu, right? Or can I spread the flu even if I feel well?

Your chance of spreading the flu is significantly reduced if you have been vaccinated. But whether you’re vaccinated or not, you can be a carrier of the flu even without symptoms. About 20 to 30% of people carrying the influenza virus have no symptoms at all. So, wash your hands after every contact you have with other people.

There are a number of steps you can take to protect yourself during flu season besides vaccination. Avoid contact with people who have the flu, wash your hands often, cover your mouth when you cough or sneeze, avoid touching your face, stay home when you are sick, clean and disinfect surfaces and shared items.

About the author

Jerome Leis

Jerome Leis

Dr. Leis is Medical Director, Infection Prevention & Control and a
staff physician in infectious diseases and general internal medicine at
Sunnybrook Health Sciences Centre.