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A patient getting a flu shot in her upper arm

Flu shot reactions: rare and misunderstood

Mary Van DorenVerified

Senior Editor

10 positive reviews
Nasal spray effectiveness

While a nasal spray exists under "FluMist," doctors recommend the flu shot. Talk to your doctor about which is best for you.

Should you get the flu shot? And what, if any, flu shot reactions can you expect to have if your body doesn't agree with the inoculation?

These are some of the questions that analysts at JustAnswer set out to answer as flu season unfolds. We looked at data spanning back to the start of 2015 in order to glean whether vaccines and flu shots are top of mind for our customers; which vaccines are most popular; and where the geographic distribution of interest for vaccines in America lies.

So, how popular are questions about vaccines in general? Not especially. Only about 6 percent of questions in the entire medical category are about vaccines. Overall, people are more curious about neurology (the study of the nervous system and its disorders) and reproductive health than they are about vaccines. On the other hand, we found more questions concerning vaccines than about dermatology, dental health, and mental health, to name a few.

A pie chart detailing the types of medical questions on JustAnswer as well as the types of vaccine questions on the site.
Overall, vaccine questions only make up 6 percent of all medical questions on JustAnswer. Flu shot questions, however, are the second most popular vaccine question.

Although vaccines aren't necessarily top of mind for JustAnswer customers, questions about flu shots figure prominently. In fact, flu shot questions are second in popularity only to varicella, or chickenpox, questions, pacing questions about hepatitis, tetanus, and shingles vaccines. (See above.) Interestingly, questions about Japanese encephalitis on JustAnswer outnumbered questions about measles, mumps, and rubella (MMR) vaccination, as well as questions about human papillomavirus (HPV) vaccination.

Few recipients of the flu shot experience any sort of symptoms. Still, we were able to piece together the most common flu shot reactions based on semantic analysis. Allergies, rashes, and itching together made up a whopping 53 percent of customer complaints. 19 percent of customers listed fatigue or general malaise, while 8 percent said nausea or vomiting was a problem.

A bar chart detailing the most common flu shot reactions people have
Allergic reactions, as well as rashes and itchiness, comprise over half of the flu shot reactions people listed while talking to Experts on JustAnswer.

When it comes to web traffic, Kentucky and nearby Mississippi saw the greatest change in visitors to JustAnswer pages about vaccines from 2016 to 2017, recording almost 800 percent and 550 percent increases, respectively. When controlling for state population, the District of Columbia, Georgia, and Texas rounded out the top three states most interested in vaccines on JustAnswer. If Georgia and Washington, D.C. had the same populations, D.C. would produce five page visits for every one of Georgia's.

A US state map detailing the percent change in questions about vaccines from 2016 to 2017
States like Kentucky and Mississippi, as well as those along the west coast, made up the highest absolute gains in traffic to vaccine pages on JustAnswer from 2016 to 2017.

Don't fret about flu shot reactions — the flu is much worse

Influenza, commonly known as the flu, can be a small inconvenience, or it can be deadly.

Flu spreads fast, either through the air or by touching surfaces contaminated with the virus and then touching the mouth or eyes. An effective vaccine is available, but myths and misunderstandings about the flu still run about as rampant as the virus itself. Naturally, many people are concerned about flu shot reactions and common side effects.

The flu season runs from roughly October through May. The actual content of the vaccine changes every year in order to combat the strains that scientists believe will be most prevalent.

A nurse examines a flu shot syringe
Flu vaccines contain strains of the virus that doctors think will be prominent during the year, based partly on strains of the previous year. Each year, the makeup of the flu vaccine changes.

The vaccines for the 2017-2018 flu season include:

  • Trivalent vaccine: protects against two influenza A strains – H1N1 (swine; different from the 2016-17 vaccine) and H3N2 (swine variant; (same as in last year’s shot) – and one influenza B strain (same as in last year’s shot)
  • Quadrivalent vaccine: protects against the same strains as the trivalent vaccine, as well as an extra influenza B strain

The federal Centers for Disease Control (CDC) lists the contents of the current year's vaccine here.

These vaccines are delivered via needle. There are also several other forms of these vaccines:

  • A stronger-dose version for the elderly (65+)
  • A small-needle version (also called "intradermal") for those between 18 to 64
  • An eggless version developed in animal cells rather than hen's eggs for those with egg allergies
  • A nasal spray, also called FluMist, which is approved but less effective than the flu shot
  • A needle-free shot, delivered by jet injector, which uses a narrow, high-pressure stream to inject the vaccine without a needle. It is approved for adults between18 to 64.

Just like last year, the CDC is not recommending the nasal spray, based on lack of effectiveness.

A nurse administers the nasal spray flu vaccine, also called FluMist
During flu season, those with a needle phobia sometimes opt for nasal spray. Although it is an option, it's typically less effective than the flu shot.

Doctors to urge people to get each year’s new vaccine because of the constantly-shifting strains of the flu, assuming that last year’s vaccine will be less effective. The best time to get the vaccine is as early in the season as possible. This usually works out be in September or early October.

Will my flu shot reaction be worse than getting the flu?

It's highly unlikely that your flu shot reaction will be worse than actually getting the flu.

Flu can be a serious disease; any flu infection carries a risk of serious complications, hospitalization or even death, even among otherwise healthy children and adults. Flu shots, on the other hand, tend to either be inactivated, meaning that the components of the virus that can make you sick have been rendered inert, or don't contain any of the flu virus at all.

You may feel a little under the weather after your flu shot, but chances are you'll feel much worse if you actually come down with the flu.

According to the CDC, most people who get the flu will have mild illness and won't need medical care or antiviral drugs, recovering in less than two weeks. Still, some people, such as children younger than 5, older adults (65+) and pregnant women, as well as those with certain medical conditions, are more likely to get flu complications that can result in hospitalization and sometimes death. For this reason, experts believe that getting vaccinated is a safer choice than risking illness.

Flu shot side effects

Flu vaccine side effects for most people are mild, and usually last less than two days. These include:

  • Soreness, redness, and/or swelling from the shot.
  • Headache
  • Low-grade fever
  • Nausea
  • Muscle aches
  • Fainting

The CDC recommends that you call your doctor if you show any of these flu jab side effects.

Swelling at the site of a flu shot
Swelling on the injection site of the flu vaccine is a common side effect. More serious reactions include fevers and allergic reactions.

Dr. William Schaffner, a preventive medicine and infectious disease expert at Vanderbilt University School of Medicine, notes that only about 1 to 2 percent of people who get a flu shot will have fever as a side effect. According to Expert Onlinedoc, a temperature up to 101 degrees is a normal reaction after getting a flu shot.

Rare but more serious flu shot symptoms involve allergic reactions, usually within a few minutes to a few hours after the vaccination, and can include:

  • Difficulty breathing
  • Swelling around the eyes or lips
  • Hives
  • Racing heart
  • High fever

The CDC advises that if you experience serious side effects, you should call emergency services and get to the nearest hospital. One JustAnswer customer experienced numbness going up the neck, along the top of the shoulders and in the upper arms, plus a flushed face and hives. Both his local doctor and the Expert on JustAnswer prescribed Benadryl, an antihistamine, which soothed the symptoms – for a while.

Unfortunately, as Expert Dr. Mo explains, “The shot will leave your system usually in the first week. But the effects can last a little longer.”

“Allergic reactions can last anywhere from 1 week up to 3 months. They generally get milder and milder as time goes on, but unfortunately it isn't easy to predict the duration."

A JustAnswer expert poses in front of a flu immunization bus
Dr. Mo, an expert on JustAnswer, has treated patients whose reactions to the flu shot have lasted for three weeks. If your reaction is serious, or it's lasted for more than three weeks, see a doctor.

Allergic reactions to the flu shot often result from an underlying allergy to egg protein that many vaccines contain. They may also result from another allergy to any one of the ingredients present in the vaccine. The doctor or nurse administering the flu shot should ask you about allergies before proceeding. If you have any specific questions about flu shot ingredients, talk to your doctor before getting vaccinated.

Why do I feel sick even though I’ve had the shot?

One of the many misconceptions about the flu vaccine is that it will actually give you the flu. However, this is just not possible. The CDC explains that flu vaccines given with a needle are currently made in two ways: The vaccine is made either with flu vaccine viruses that have been ‘inactivated’ and are therefore not infectious; or with no flu vaccine viruses at all.

Often, people who’ve had the shot believe they’ve later gotten flu anyway. Yes, it’s possible to get the flu because the vaccine can vary in how well it works, and some people who get vaccinated may still get sick.

However, the common cold has symptoms similar to the flu, and can be rampant during flu season. No medication or vaccine prevents a cold, not even a flu shot. Also, if you were exposed to the flu just before getting vaccinated or during the two-week period it takes the body to develop immune protection after getting the shot, you could come down with flu after having the shot.

Also, as mentioned above, the flu consists of thousands of strains that are constantly evolving, and each year’s vaccine is an educated guess about which strains will be dominant. If you run up against a strain that the vaccine wasn’t designed to prevent, you could still get the flu.

A microscopic view of a strain of the flu virus
A microscopic image of a flu virus strain. Since there's guesswork involved in determining which strains will be prominent, and since strains can also mutate, it's hard work for immunologists.

Finally, a common myth about flu shot reactions is that the vaccine makes it more likely for you to get other respiratory illnesses. The CDC notes that this is based on a single study, which researchers have completely failed to replicate, making it unlikely to be true.

Who should not get the shot, and who should check with their doctor first

Children younger than 6 months should not be vaccinated. Other than that, check with your doctor or pharmacist first if you:

  • Have had a severe allergic reaction to a flu vaccine in the past
  • Are very ill – wait until your health improves before getting the shot
  • You’ve had Guillain-Barré syndrome that happened after you got the flu vaccine

When it comes to flu shot reactions, there’s simply little need to worry unless you fall into one of the at-risk categories – and even then, the risk of flu and serious flu-induced illnesses means you should at least check with your doctor before making a decision to skip it.

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