Nov. 10, 2021 -- The flu shot is far less effective than the COVID-19 vaccines, causes more side effects, and targets an infectious disease that most people survive, with the flu killing only a fraction of those who die from coronavirus.

So should you even bother getting a flu shot this year?

Health experts say the short answer is yes.

They point to three key reasons federal health authorities recommend the flu shot for everyone 6 months old and older:

  1. The vaccine is the most effective way to protect yourself and others from the flu, which kills an average of 36,000 Americans every year, and flu-related complications.
  2. Side effects from the shot are very rare and typically mild-- primarily soreness where the needle went into your skin, headache, fever, nausea, muscle aches, and fatigue.
  3. With COVID-19 expected to surge in coming weeks as Americans travel and gather for the winter holidays, this is not the year to risk becoming hospitalized for the flu or other preventable diseases.

“It's really important to reduce the risk of getting the flu, which is what the flu vaccine does,” says Leana Wen, MD, an emergency medicine doctor and public health policy professor at George Washington University. “This is particularly important this year, when we could very well face the confluence of influenza and COVID-19.”

She notes that flu shots, as well as COVID-19 vaccines, don’t protect only those who receive them.

“Getting vaccinated against both the flu and COVID protects against both and reduces the likelihood of spreading these viruses to others,” says Wen, author of the newly published book Lifelines: A Doctor’s Journey in the Fight for Public Health.

Gigi Gronvall, MD, an infectious disease specialist with the Johns Hopkins Center for Health Security, agrees that getting a flu shot is critical this year, noting influenza can also lead to other life-threatening illnesses, such as pneumonia, which kills tens of thousands of Americans annually.

“For people who say, ‘Well, it’s just the flu’ -- the flu is no joke,” says Gronvall, an immunologist and associate professor at the Johns Hopkins Bloomberg School of Public Health. “Speaking as someone who was actually hospitalized when I had just turned 30 after getting flu and then pneumonia, it can lead to unpleasant additional diseases.”

If you’re on the fence about getting a flu shot this year, here’s a breakdown of what you need to know.

Why Flu Shot Effectiveness Varies

Flu viruses are constantly changing and evolving, which is why we need annual flu vaccines, whose composition varies year to year. About 144 national influenza centers in over 110 countries conduct year-round surveillance for influenza to determine each year’s vaccine formulation.

The CDC works with global health authorities to track and identify which strains are making people sick based on that surveillance and recommend which varieties vaccine manufactures should include in the current season’s flu shot.

That’s why the flu shot’s effectiveness varies from year to year, falling to just 43% during the 2019-2020 flu season, for instance.

By contrast, the COVID-19 virus has not changed as rapidly or significantly, even though some new strains, such as the Delta variant, have emerged since the start of the pandemic. As a result, the vaccines developed to target the coronavirus have not required new formulations. At least not yet.

All three COVID-19 vaccines approved for use in the U.S. have remained remarkably effective -- 86% to 95% -- with boosters only recently recommended by federal officials to maintain those levels of efficacy.

“The [flu] shot is not as effective as the vaccine for COVID because it has to be matched against the circulating strains of flu every year, and sometimes the match isn’t great,” explains Gronvall. “You can get hit with a virus that the vaccine was not designed to protect against.”

Several factors can determine whether the flu vaccine is a good or bad match.

The first is timing. It takes about 6 months for vaccine manufacturers to produce and ship the annual flu shot. Sometimes a new influenza strain can emerge during the vaccine’s production, which means the annual shot won’t be protective against it.

Secondly, the FDA requires influenza vaccine viruses to be grown in chicken eggs or cells. But some strains grow poorly in eggs, making it a challenge to develop effective vaccines.

These factors help explain why the flu vaccine was only 19% effective in 2014-2015 but about 60% effective in 2010-2011. (In other words, in 2014-2015, only 19% fewer adults who got the shot came down with the flu compared with those who were unvaccinated, while in 2010-2011 that percentage was 60%.)

Still, flu vaccination prevents millions of illnesses and flu-related doctor’s visits each year.

The CDC estimates, for instance, that during last year’s flu season, vaccines prevented an estimated 7.5 million influenza illnesses, 3.7 million flu-related medical visits, 105,000 hospitalizations, and 6,300 deaths.

“Even in bad-match years, the flu shot reduces risks of hospitalization and death from the disease, and it is always a good idea,” Gronvall notes.

Studies have also shown that flu vaccination reduces the severity of illnesses and the risk of death for people who get vaccinated but still get sick. One recent study found that adults who were vaccinated had a 26% lower risk of being admitted to a hospital intensive care unit (ICU) and a 31% lower risk of death from flu compared to those who were unvaccinated.

A second study found even stronger results, showing vaccinated adults who were hospitalized with flu were 59% less likely to be admitted to the ICU than those who had not been vaccinated.

What’s more, research shows vaccination significantly reduces the risk of flu-associated hospitalization for children, pregnant women, people with heart disease, lung conditions (such as chronic obstructive pulmonary disease), diabetes, and other chronic health problems.

And another factor to consider: Getting vaccinated protects people around you, including those who are more vulnerable to serious flu illness like babies and young children, older people, and those with certain chronic health conditions.

Flu Vs. COVID-19 vaccines: Risks and Benefits

Despite these facts, only about half of Americans get a flu shot every year.

One reason: Fear of side effects. While it is true that the flu vaccine causes more negative side effects and allergic reactions than the COVID-19 shots, they are very rare.

The flu vaccine causes mild reactions in some people. More serious allergic reactions to flu shots can occur but are rare and not usually life-threatening. They typically occur in people who are allergic to vaccine components, such as egg protein or other ingredients.

CDC research suggests the flu vaccine may also be associated with Guillain-Barre syndrome at a rate of 1 or 2 cases per million people vaccinated. But this rate is much lower than the risk of severe complications from flu, which can be prevented by flu vaccine.

By contrast, clinical trials and ongoing research into the COVID-19 vaccines show the potential negative side effects are extremely rare. The Pfizer-BioNTech and Moderna mRNA vaccines have “appeared” to trigger anaphylaxis, an allergic reaction that is treatable with epinephrine, and may be associated with mild heart inflammation in young adults in a few rare cases. As a result, the CDC requires vaccination sites to monitor everyone for 15 minutes after their shot and for 30 minutes for people with a history of severe allergies, and the FDA has placed a warning label on the vaccines about the potential for heart inflammation.

The Johnson & Johnson vaccine has been linked to a handful of rare cases of Guillain-Barre syndrome and a treatable blood-clotting disorder.

But health experts note these side effects from the COVID-19 vaccine are very rare and say the risks don’t outweigh the benefits, especially when you consider more than 7.5 billion shots have been given worldwide -- 428 million in the U.S. alone (59% of the population) -- according to Johns Hopkins University.

For perspective, more than 5 million people have died from COVID-19 worldwide, while the U.S. death toll has topped 754,000.

What Can We Expect This Year?

Looking ahead, the CDC reports a few things are different for the 2021-2022 flu season.

For one thing, all flu vaccines will be designed to protect against the four viruses -- two influenza A strains and two influenza B strains -- that research suggests will be most common in the U.S. this year

Agency officials note the flu vaccines and COVID-19 vaccines can be given at the same time.

So far, seasonal flu activity in the U.S. has been low, but the number of cases reported by public health laboratories has started rising in recent weeks, a trend likely to continue as the winter holidays approach, the CDC reports.

Health experts predict this year’s flu season will be more severe than last year’s, with more people traveling, easing up on COVID-19 precautions, and spending less time sheltered at home and keeping their distance from others.

In 2019-2020, the U.S. experienced one of the mildest flu seasons in history as a result of all the handwashing, social distancing, and mask wearing that COVID-19 brought.

Only about 700 Americans died from the flu, compared with 22,000 the year before and 34,000 two seasons ago, according to the CDC.

The good news is that the same precautions that help prevent COVID-19 can also keep the spread of influenza in check. So if Americans continue to those practices, this year’s flu season might be milder than usual.

The bad news: Last year’s mild flu season left vaccine researchers with less data than usual to use to create this year’s influenza vaccine. That could increase the odds of a poorer vaccine match.

And with fewer Americans following COVID-19 precautions and more people returning to pre-pandemic activities, influenza is likely to be more widespread this season.

CDC Director Rochelle P. Walensky, MD, says the unpredictability of the coming flu season is why everyone 6 months old and older should get vaccinated.

“If you are unsure about getting a flu vaccine, please take the time to get the information you need to make the right choice for your health and to get vaccinated,” she said during a recent “Flu Vaccination Kickoff” virtual press conference that was hosted by the CDC and the National Foundation for Infectious Diseases (NFID).

“The COVID-19 pandemic is not over, and the risk of both flu and COVID-19 circulating could put additional strain on hospitals and frontline health care professionals.”

William Schaffner, MD, says that now is not the time to let our guard down, despite last year’s mild flu season.

“While flu activity was historically low during the 2020-2021 flu season, we could see flu activity surge this season, with relaxed COVID-19 mitigation strategies, increased travel, and the reopening of schools and businesses,” says Schaffner, who is also the NFID medical director. “The best way to protect yourself against flu is to get an annual flu vaccine. Even in cases when flu vaccination does not completely prevent infection, it can reduce the duration and severity of illness and can help prevent serious complications, including hospitalization and death.”

For more information, visit the CDC’s seasonal flu vaccines primer here.

Show Sources

National Foundation for Infectious Diseases: “US Health Officials Urge Vaccination Amid Concerns About Influenza Resurgence During Ongoing Pandemic.”

CDC: “Disease Burden of Flu,” “Seasonal Flu Vaccines,” “Pneumonia,” “Selecting Viruses for the Seasonal Influenza Vaccine,” “Past Seasons Vaccine Effectiveness,” “Estimated Influenza Illnesses, Medical Visits, and Hospitalizations Averted by Vaccination in the United States – 1029-2020 Influenza Season,” “2021-22 flu season FAQs,”  “What’s New for 2021-2022,” “Weekly flu surveillance.” 

USA Facts: "61,000 people died in the worst flu season of the past decade. COVID-19 has killed eight times that many."

Institute for Health Metrics and Evaluation: “COVID-19 Projections.”

Leana Wen, MD, Research Professor of Health Policy and Management, George Washington University.

Gigi Gronvall, PhD, associate professor, Johns Hopkins Bloomberg School of Public Health.

Scientific American: “Flu Has Disappeared for More Than a Year.”

Vaccine: “Does influenza vaccination attenuate the severity of breakthrough infections? A narrative review and recommendations for further research,” “Influenza vaccine effectiveness in preventing influenza-associated intensive care admissions and attenuating severe disease among adults in New Zealand 2012–2015."

Yale Medicine: “Comparing the COVID-19 Vaccines: How Are They Different?”

Bloomberg: “More Than 7.25 Billion Shots Given: Covid-19 Tracker.”

Johns Hopkins: “Coronavirus Resource Center.”

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