Skip to main content
Family of four plays at the beach with coastline in background

Why do I need a flu shot this season?

November 09, 2021 | UCI Health
Young couple laying in bed, suffering from flu symptoms.
"People who've been vaccinated for flu have less severe episodes of illness and recover more quickly,” says Dr. Maryam Rahimi, a UCI Health specialist in internal medicine and primary care. 

Flu season is officially here: The first Orange County case of influenza was confirmed on Oct. 22 by the county’s healthcare agency.

That means you should schedule an annual vaccine for yourself and anyone in your household over six months of age if you haven't already, says UCI Health primary care physician Maryam Rahimi, MD.

Last year’s flu season was milder than most, thanks in no small part to COVID-19 safety measures — masking, physical distancing, closures of schools, offices and businesses, as well as restrictions on gatherings in large public spaces.  

Fewer than 1,700 U.S. flu cases were confirmed between September 2020 through May 2021. It’s a shockingly tiny number compared to the 35 million flu-related cases, including 20,000 deaths and 380,000 hospitalizations, recorded during the 2019-2020 flu season.

A guard against the flu’s spread

Now, however, with children back in classrooms and many people returning to work, congregating in public places and traveling, this year’s strains of influenza can spread more easily and pose a danger for the vulnerable among us.

Without the vaccine, most people recover from the flu within 10 days, explains Rahimi, a professor of internal medicine and primary care at the UCI School of Medicine. “But for some, the flu can lead to pneumonia and death.”

Getting the annual flu vaccine can help guard against that, she says. “We have strong evidence that vaccination can prevent infection or reduce the severity of the disease.”

Who should get a flu shot?

Most people over the age of six months should get an annual flu shot, ideally by the end of October, the U.S. Centers for Disease Control and Prevention (CDC) recommends.

It's not too late, however, because flu viruses continue to circulate throughout the fall and winter, peaking between December and February, and sometimes stretching into May.

For people who are age 65 and older, flu shots are critically important, Rahimi says. “Immune response tends to decline with age and complications can be more severe.”

Vaccination is also vital for:

  • Healthcare workers
  • People with chronic health conditions and those who are immune compromised, undergoing chemotherapy or are obese, which can increase the risks of complications
  • Women who are pregnant or planning to become pregnant
  • Native Americans, who are greater risk for developing serious complications
  • Caretakers and others in close contact with people who have chronic conditions, are under six months of age or over age 65

Who shouldn’t get vaccinated?

Some people should not get a flu shot or consult their doctor beforehand. They include:

  • Children under six months of age
  • Anyone who has had a severe, potentially life-threatening allergic reaction to a previous flu vaccine (Note: Egg-free vaccines are available for those who have severe reactions to eggs.)
  • People with moderate-to-severe illnesses (Note: It’s safe for people who have a cold, sore throat, sinus infection or other mild illness.)
  • People with active COVID-19 infections should wait until they recover
  • People with Guillain-Barré syndrome, a rare autoimmune disorder, should consult their doctor

All of these individuals still need protection, Rahimi says, adding, “If you are unable to get a flu shot, talk to your primary care doctor about your options. And continue to wear a mask, keep your distance from people with flu-like symptoms and practice good hand hygiene.”

How effective is this year’s vaccine?

Flu viruses are constantly changing. The CDC conducts year-round surveillance of circulating flu viruses and uses this and other data to recommend the four most prevalent strains to include in vaccine production for both the southern and northern hemispheres.

This season’s vaccine targets four viruses: H1N1, H3N3 and two types of influenza B. Historically, the effectiveness of the vaccine varies from 40% to 60% each year.

“It’s too early to predict how effective this year’s vaccine will be,” Rahimi says. “However, studies show that people who've been vaccinated for flu have less severe episodes of illness and recover more quickly.”

What’s my risk without a vaccine?

We may well be facing a more severe influenza season, experts say.

Moreover, Rahimi says, “Last year’s mild flu season means we may have less immunity and be more susceptible to infection this year.”

And like last season, the ongoing COVID-19 pandemic continues to complicate matters.

Physicians across the country are being encouraged to test anyone with an acute respiratory illness for both influenza and the virus that causes COVID-19.

A positive test for one does not preclude a positive test for the other.

Can the vaccine give me flu?

The short answer is no.

“Over the years, I’ve heard people say that every time they get the vaccine, they get the flu,” Rahimi says. “But you cannot get the flu from the vaccine because it’s made from a dead virus.”

Vaccinated people do sometimes get the flu, but that is usually because they were exposed to a virus shortly before getting the shot or within the two-week period it takes the body to develop immunity, according to the CDC.

“Another reason vaccinated people may have experienced flu symptoms is that they were exposed to a flu strain not included in that year’s flu shot formulation,” says Rahimi.

In addition, many other respiratory viruses are also in circulation, including rhinoviruses responsible for common colds, which have similar symptoms to the flu — and COVID-19.

Are there side effects?

The most common side effects of the flu vaccine are soreness, redness or swelling at the injection site.

A few people may experience headache, fever, nausea, muscle aches or fatigue. These usually go away within 48 hours.

High-dose vaccinations are usually recommended for people over age 65. “Sometimes these can cause slightly more severe side-effects, including rare gastrointestinal symptoms,” Rahimi says.

However, a high fever, behavioral changes or signs of an allergic reaction, usually within the first few hours after the vaccination, may be cause for concern and worth a call to your doctor.

While life-threatening reactions to the flu vaccine are extremely rare, the CDC recommends that anyone experiencing a severe allergic reaction call 911 or get to the nearest hospital.

Don’t forget COVID-19

It is safe to get your flu vaccination at the same time as a COVID-19 vaccine or booster if you haven’t already had one, according to the CDC.

This doesn’t change the effectiveness of either vaccine or cause more side effects, but Rahimi advises getting the shots in different arms.

“If there is a reaction at the injection site, we will know which vaccine caused it.”

This season, getting both vaccines protects all of us, she says.

“Vaccination still remains the best way to prevent both influenza and COVID-19.”

Related stories