Editor's note: This story was most recently updated Nov. 10, 2021.

The 2020 flu vaccine was 45% effective against the flu so far last season, CDC figures show.

It worked better against the B strain of the flu (50% effective) than the A strain (37% effective.) And overall it worked better in children and teens ages 6 months to 17, with a 55% effectiveness rate.

The effectiveness rate for vaccines typically ranges from 40% to 60%, the CDC says, and the vaccine can help prevent illness, hospitalization and death.

The news come as flu activity remains high. 

After increasing for several weeks, the number of cases decreased slightly, the CDC says.

An A strain of flu remains more common now. Earlier in the season, a B strain was more common.

A B virus has been diagnosed more among children and young adults up to 24 years old, while an A virus has been more common among adults 65 and older. Of the 105 pediatric deaths from flu, 72 are linked to the B virus. 

Previously, officials had said this year's flu season was on track to be one of the worst in decades.

The agency estimates there have been at least 29 million flu illnesses, 280,000 hospitalizations and 16,000 deaths from flu so far this season. 

Public health officials say that getting a flu shot can help protect against getting sick and getting hospitalized for flu. 

The flu is a contagious disease, and it can cause mild to severe symptoms along with life-threatening complications, even in young, healthy children and adults. Since 2010, the flu has killed from 12,000 to 79,000 people annually in the U.S. and affected about 9.3 million to 49 million annually.

Here is what else to know about flu.

What is the latest news on the flu season?

The CDC updates flu activity on a weekly basis. While numbers were low the first week of November 2021, data showed an increase in activity over the previous weeks.

The CDC also monitors with a map of the activity to help you monitor case numbers near you.

When does flu season begin and end?

Although you can get the flu anytime, flu season starts in October and can go as late as March and even April. But it usually peaks in the U.S. in February, says William Schaffner, MD, a professor of infectious diseases and preventive medicine at Vanderbilt University Medical Center in Nashville.

When is the best time to get a flu shot?

In general, everyone over 6 months of age should get vaccinated -- the earlier the better for getting the vaccine. Late September is a good time, Schaffner says, and even into October and beyond. With the length of last year’s flu season, the idea of booster shots has been discussed. Schaffner says that idea is not backed by studies.

How well is this year's vaccine working against the flu virus?

The 2020-2021 flu season was essentially non-existent because of the masking for covid.  The 2021-2022 is expected to experience more cases.

Remember that there are many strains of the two types of flu viruses -- A and B -- that infect humans. In order to have flu shots ready for flu season, experts have to decide, months in advance, which strains to include in the vaccine. Because strains can change quickly, the vaccine is not always a good match.


The effectiveness rate for vaccines typically ranges from 40% to 60%, the CDC says, and the vaccine can help prevent illness, hospitalization and death.

Where do I get the flu vaccine?

It's offered at doctors' offices, clinics, health departments, college health centers, pharmacies, and at many offices and some schools.

Many insurance plans pay for the annual vaccination, and older adults covered under Medicare Part B can get the vaccine free, with no copay or deductible.

To find a source for vaccines in your area, go to the Vaccine Finder (https://vaccine.healthmap.org).

What about the nasal spray flu vaccine?

The nasal spray vaccine, FluMist, is once again being recommended by the CDC for adults and children. In recent flu seasons, the CDC and the American Academy of Pediatrics had recommended flu shots only for kids because of questions about well the spray worked. But the manufacturer appears to have improved the spray, so the CDC and AAP say parents can go either way -- shots or spray.

Although it didn’t work well against H1N1 viruses, it did against some B viruses and H3N2 viruses. The CDC says the manufacturer has produced a new H1N1 vaccine that may work better this year, though no published effectiveness estimates are available yet. It’s available for children 2 and older who don’t have a compromised immune system.

How do experts decide what to put into the flu vaccine?

During flu season, experts study samples of the viruses circulating to find out how well the vaccine protected against those viruses. They use that information to help make their decision for the next one. This year, most vaccines will protect against two A strains -- H1N1 and H3N2 -- and two B strains. All regular dose flu shots this year will be quadrivalent, meaning they will protect against four strains.

Like all other vaccines, the one for flu isn't perfect, but it cuts the risk of illness from 30% to 60% in the general population, the CDC says. In general, vaccines work better against influenza B and influenza A (H1N1) viruses than they do against influenza A (H3N2) viruses, the CDC says.

Is there progress on a universal flu vaccine?

The National Institutes of Health recently awarded the University of Georgia an initial $8 million grant to develop a flu vaccine that would cover multiple strains in a single dose. The university is working with 14 other universities on the project . Ted Ross, PhD, director of the university’s Center for Vaccines and Immunology, said they may be able to start testing a vaccine on people sometime next year. Ross said the goal is to help people most vulnerable to flu. Other researchers have been working on a universal flu shot, as well.

Who gets hit the hardest?

Children, older adults, pregnant women, anyone with a chronic medical condition, and health care workers are especially vulnerable to getting the flu or to having complications such as pneumonia, bronchitis, and sinus and ear infections, the CDC says.

Children younger than 2 are especially vulnerable. Those ages 6 months and under are also much more likely to get complications, but they're too young to be vaccinated, so the best idea is to be sure everyone in contact with them is vaccinated.

Adults ages 65 years and above are at greater risk than younger, healthy adults due to weakened immune systems. Typically, these older adults account for most flu-related deaths and more than half of flu-related hospitalizations.

Pregnant women, as well as those who have delivered a baby in the previous 2 weeks, are more likely to have a severe illness than women who aren't pregnant.

Anyone with a chronic medical condition is more likely to have complications. These conditions include:

  • Asthma
  • Diabetes
  • Heart disease
  • Obesity
  • A compromised immune system due to cancer, HIV, or other conditions

Is one type of vaccine better than another?

While the quadrivalent vaccine protects against the two A strains and the two B strains, the CDC says there is no preference among the recommended and approved vaccines. Ask your doctor which is best for you. Different vaccines are approved for different age groups.

About 80% of this year’s supply will be quadrivalent vaccines.

What types of flu shots are available this year?

For the 2019-2020 season, there are several vaccines:

Children who have never been vaccinated against the flu will need two doses, spaced at least 4 weeks apart.

Who should not get a flu shot?

Anyone who got Guillain-Barre syndrome within 6 weeks of a previous flu vaccination should not get vaccinated, the CDC says. Nor should anyone with a known severe, life-threatening allergy to any ingredients in a vaccine.

What about pregnant women? A recent study linked flu vaccine and odds of miscarriage.

The CDC says pregnant women should get the flu shot, but not the nasal spray.

Schaffner says there’s been no further research to back up a study, published in the journal Vaccine in September 2017, in which researchers found a link -- but could not prove cause and effect -- between women who were vaccinated against influenza A (H1N1) strains for two consecutive seasons and miscarriage.

But previous research had not found a higher risk, says Schaffner, who's also a professor of preventive medicine at Vanderbilt University School of Medicine, Nashville. And subsequent studies found no further evidence to support the miscarriage link, he says. The finding appeared to be a statistical fluke, he says.

Pregnant women who get vaccinated also cut the chances of flu in their baby, Schaffner says. "Some of that protection goes across the placenta and protects the baby for the first 6 months" before immunization is recommended, he says.

How long does it take for the flu shot to become effective?

It takes about 10 days to 2 weeks for the vaccine to reach its top strength, says Schaffner.

What are common symptoms of the flu?

They usually come more suddenly than cold symptoms. They include fever, feeling feverish, the chills, and having a cough, sore throat, runny nose, muscle or body aches, headache, and fatigue. Less common are vomiting and diarrhea. Children are more likely to have vomiting and diarrhea than adults are, the CDC says.

Not everyone with the flu has a fever.

What should I do if I think I am getting the flu?

Stay home, rest, and avoid contact with others except to get medical care if needed, experts say. Avoid contact with others for at least 24 hours after the fever subsides to avoid spreading the flu.

Be on the lookout for emergency warning signs that you may be getting serious flu-related complications, the CDC says.

In children, these include:

  • Fast or troubled breathing
  • Bluish skin color
  • Severe crankiness
  • Fever plus a rash
  • Lack of interaction
  • Not drinking fluids
  • Symptoms that improve then return with fever and a worse cough

In adults, they include:

  • Breathing trouble
  • Pain or pressure in the chest or belly
  • Dizziness or confusion
  • Severe or persistent vomiting

Symptoms that improve but then return with a fever and worsening cough.

Emergency flu symptoms kids

What are the treatments for the flu?

The FDA in 2018 approved the first new flu treatment in nearly 20 years: baloxavir marboxil (Xofluza). The new treatment joins the other three antivirals for flu: oseltamivir (generic or Tamiflu), peramivir (Rapivab), and zanamivir (Relenza).

Antiviral drugs can lessen your symptoms and shorten sick time by 1 or 2 days, according to the CDC. These are prescription medicines in various forms, such as pills, liquids, an inhaled powder, and an IV solution. Ask your doctor if they are right for you.

They may also have side effects. Tamiflu may cause nausea and vomiting, and it may make headaches and psychiatric effects more likely. And in a recent study, it didn’t lessen complications.

It's important to start the drugs early, as studies show they work best when started within 2 days of getting sick. But your doctor may decide they can still be helpful if started later than that.

Besides getting vaccinated, what else can help lower the chance of getting the of flu?

Everyday preventive actions are important. Avoid people who are ill, and practice good hygiene such as washing your hands often and covering your cough. If you are sick, stay home.

HealthDay contributed to this report.

WebMD Medical Reference


CDC: “Frequently Asked Influenza (Flu) Questions: 2019-2020 Season,” “Update: Influenza Activity in the United States During the 2018-19 Season and Composition of the 2019-20 Influenza Vaccine,” “Prepare Your Practice To Fight Flu,” “Live Attenuated Influenza Vaccine [LAIV] (The Nasal Spray Flu Vaccine),” “FluView,” "Key Facts About Seasonal Flu Vaccine," "Vaccination: Who Should Do It, Who Should Not and Who Should Take Precautions," "Flu Symptoms & Complications," "What You Should Know About Flu Antiviral Drugs," "How Effective Is the Flu Vaccine?" "Pregnant Women and Influenza (Flu)."
William Schaffner, MD, medical director, National Foundation for Infectious Diseases; professor of preventive medicine, Vanderbilt University School of Medicine, Nashville.

American Academy of Pediatrics: “AAP Updates Vaccine Recommendations for 2019-2020 Flu Season.”

BMJ: “Oseltamivir for influenza in adults and children: systematic review of clinical study reports and summary of regulatory comments.”

Vaccine: “Association of spontaneous abortion with receipt of inactivated influenza vaccine containing H1N1pdm09 in 2010-11 and 2011-12.”

Scott Pauley, press officer, News Media Branch, Division of Public Affairs, CDC.

University of Georgia: "NIH awards up to $130M to develop universal flu vaccine."

WSB-TV: "Univeristy of Georgia awarded largest grant ever to develop new universal flu vaccine."

HealthDay: "Get Vaccinated Before the Flu Takes Hold: CDC."

MMWR: "Update: Influenza Activity — United States and Worldwide, May 19–September 28, 2019, and Composition of the 2020 Southern Hemisphere Influenza Vaccine."

News release, Los Angeles County Department of Public Health.

News release, Indiana State Department of Health.

Wisconsin Department of Health Services: "RESPIRATORY VIRUS SURVEILLANCE REPORT."

News release, North Carolina Department of Health and Human Services.

Monroe County Department of Health.

Arkansas Department of Health.

News release, South Carolina Department of Health and Environmental Control.

Oklahoma State Department of Health, "OK FluView: Weekly Influenza Activity Summary."

Minnesota Department of Health, "Weekly Influenza & Respiratory Illness Activity Report."

JAMA Pediatrics, "Association of Seasonal Severity and Vaccine Effectiveness With Influenza Vaccination Rates in Children."

Connecticut Department of Public Health.

Texas Health and Human Services.

Los Angeles Fire Department. 

Missouri Department of Health and Senior Services.

Scott Pauley, spokesman, CDC.

CDC: "2019-2020 U.S. Flu Season: Preliminary Burden Estimates."

Maricopa County, AZ.

Texas Health and Hunan Services.

Ohio Department of Health.

CNN: "US on track for one of the worst flu seasons in decades."

CDC: "Interim Estimates of 2019–20 Seasonal Influenza Vaccine Effectiveness — United States, February 2020."




© 2021 WebMD, LLC. All rights reserved.