Given the nation’s antivaccine movement and the annual safety myths and efficacy quibbles about the seasonal influenza vaccine, public health officials are keeping it simple this year: A flu shot can keep you out of the hospital and the morgue.

The Centers for Disease Control and Prevention (CDC) presented two studies recently in Washington, DC, at the IDWeek 2019 conference showing that flu vaccinations prevented hospitalization in children and deaths in adults.

“Last year [in the 2017-2018] flu season, about a million people were hospitalized and more than 79,000 died,” Kristina Bryant, MD, IDWeek Chair, said at an Oct. 4, 2019, press conference. “New research presented at this meeting confirms why it is so important for everyone 6 months and older to get a flu shot every year. Vaccines work. Flu vaccine reduces the risk of hospitalization in children and the risk of death in adults.”

In one study, flu vaccination of children in the 2016-2017 and 2017-2018 seasons reduced their risk of hospitalization by 48%.1 In the other study2 presented at IDWeek, prior flu vaccination reduced mortality by approximately one-third in adults hospitalized with influenza. The researchers analyzed data from more than 40,000 adults hospitalized with lab-confirmed flu across five influenza seasons in more than 250 acute care hospitals in 13 states.

“Our large population-based study showed that flu vaccine reduced the risk of severe outcomes, including death, among adults who were hospitalized despite getting vaccinated,” said Shikha Garg, MD, MPH, lead author of the study and a medical officer in the CDC Influenza Division.

This message was also front and center at the annual flu meeting of the National Foundation for Infectious Diseases (NFID) in Washington, DC, recently. “We need to emphasize the importance of partial protection,” said William Schaffner, MD, medical director at the NFID. “We need to remember that, even if you get influenza, after having received the vaccine, you are likely to benefit by having a less severe and shorter illness. And more important, you’re less likely to suffer the complications, including pneumonia, hospitalization, and dying.”

Ethical Obligation

Infection preventionists and their clinical colleagues should redouble efforts to immunize staff and patients for influenza, as an NFID national survey3 showed that almost half of U.S. adults said they will decline vaccination for the 2019-2020 flu season.

“The other point from the survey that I think is important to emphasize is that U.S. adults said they mostly turn to healthcare professionals for information about influenza and vaccines,” Schaffner said. “It’s a reminder for all of us that the recommendation of a healthcare professional matters. We need to insist - diplomatically - on vaccination for our patients.”

The importance of immunizing healthcare workers was also stressed at the NFID meeting by Alex Azar, JD, Secretary of the Department of Health and Human Services (HHS).

“We estimate 81% of all healthcare workers got vaccinated last season. Which is great, but it’s not uniform,” he said. “Only 68% of long-term care workers got vaccinated. Many of them work with patients who are at the highest risk of serious flu complications. So we’ve really got to see this number increase.”

Improving healthcare worker flu vaccination in long-term care settings remains a challenge, but there are signs of improvement. An increasing number of facilities are seeking “honor roll” status aimed at reaching higher immunization rates, Amy Behrman, MD, FACP, FACOEM, told Hospital Infection Control & Prevention.

“There has been a leap forward in terms of the number of [long-term care] institutions providing proof that they belong on the honor roll,” said Behrman, co-chair of the Influenza Working Group (IWG) of the National Adult and Influenza Immunization Summit.

The IWG partnered with the Immunization Action Coalition (IAC) to encourage nursing homes to join the flu immunization honor roll for healthcare facilities. To be included on the honor roll, a facility must require influenza vaccination for employees and must include “serious measures” to prevent transmission of flu from unvaccinated workers to patients, IAC states.4 “Such measures might include a mask requirement, reassignment to nonpatient-care duties, or dismissal of the employee.”

Long-term care residents are vulnerable to flu outbreaks, because they may attain only marginal immunity if vaccinated and the virus spreads easily in communal settings.

“In my opinion, the evidence supporting vaccinating healthcare personnel to protect patients is actually the strongest in long-term care,” Behrman said. “They tend to have a much higher staff turnover and, in general, their staff have much more physical contact on an ongoing basis as they help residents and patients with activities of daily living.”

Hospital immunization rates have increased in recent years, driven by mandatory policies, education about myths and misinformation, and overall awareness of how vaccines are critical to protect vulnerable patient populations. Hospitals with mandatory requirements immunized 95% of workers in the 2017-2018 flu season, according to a CDC survey.5 However, some healthcare workers have successfully challenged hospitals for failing to provide religious exemptions to flu vaccination.

“It is a patient safety issue,” Schaffner said. “That’s the principal reason healthcare workers should get immunized. I think it is both a professional and ethical obligation for us to be vaccinated.”

Vaccination also is critical to ensure healthcare teams are able to stay on the job and care for a potential upsurge in flu patients, he says.

A Coin Flip on Flu Shot

In the NFID survey conducted in August, 1,002 adults responded to questions about their attitudes and intentions regarding the current season. Overall, 60% of respondents agreed that the flu vaccine is the best preventive measure against flu-related deaths and hospitalization.

However, the survey also indicated that only 52% of respondents planned to get vaccinated this flu season. About 45% of adults and 63% of children were immunized during the 2018-2019 season, Schaffner said.

“This public opinion poll reminds us that the perceptions about effectiveness, and to some extent, safety, also truly can be barriers,” Schaffner said. “It’s important to remember that, other than a soreness at the injection site, there really isn’t any notable side effect.”

The reasons for declining vaccination included a belief that flu shots do not work (51%) and concern about side effects (34%). In addition, 22% feared they would acquire influenza from the vaccine, a persistent myth that has no basis in fact.

“Most troubling is that nearly a quarter of individuals who said they didn’t intend to get vaccinated this season are actually at greater risk for flu-related complications,” he added. “They’re either 65 years of age or older, or have underlying health issues, such as diabetes, asthma, and heart disease, that actually predispose them to the complications of influenza.”

Indeed, flu infection can aggravate underlying medical conditions and heighten the risk of heart attack and stroke, said Bill Borden, MD, a preventive cardiology specialist at George Washington (DC) University.

“An unrecognized danger of the flu is that the resulting inflammation may last for several weeks after the acute infection,” Borden said at the NFID meeting. “In fact, a study6 showed that people with underlying heart disease who have the flu are six times more likely to have a heart attack within the first week of a lab-confirmed flu infection.”

In addition, flu infection increases the risk of pneumonia for those with asthma, Borden said. In those with diabetes, influenza infection can undermine control of blood sugar levels.

“Patients with diabetes are three times more likely to die of flu complications, and six times more likely to be hospitalized,” he said.

‘Vaccine Hesitancy’

The World Health Organization lists “vaccine hesitancy” as one of the top 10 threats to public health in 2019. “The reality is, that unless we start to prioritize prevention, vaccine-preventable diseases will persist in the United States,” Schaffner said.

This “hesitancy” is being driven in part by a national anti-vaccine movement, which has driven down childhood immunizations for measles and other diseases by spreading false fears about autism and other adverse effects of vaccinations. Those concerns have been thoroughly debunked regarding the measles vaccine.7

Still, public health officials underscore the safety of the annual flu vaccine, which is manufactured every season in attempt to hit a moving target - the projected or identified circulating influenza strains based on the flu season in the Southern Hemisphere. It is an imperfect science, but the vaccine is safe, if not fully effective. That makes the public health messaging difficult, as people point to the varying efficacy of the seasonal immunization in declining the shot.

“We all know that the flu vaccine isn’t perfect, and we saw that last year’s vaccine was more effective at the beginning of the season, but less so by April, when the H3N2 virus was circulating,” Schaffner said. “That’s why it’s critical that we emphasize the importance of partial protection.”

Over the last 15 flu seasons, the CDC estimates vaccine efficacy as low as 10% in 2004-2005 to a high of 60% in 2010-2011.8

The 2018-2019 vaccine was 29% effective overall, after a strain of H3N2 influenza A emerged that was a mismatch with the vaccine. The late emergence of the H3N2 caused more severe disease and lengthened the flu season beyond expected duration, with influenza activity elevated for more than five months.

In an effort to get the best H3N2 match possible this season, public health officials delayed adding that component to the vaccine from February until March this year. The delay allowed identification of a distinct strain of H3N2 that was increasing in the United States.

“H3N2 viruses have presented an increasing challenge for vaccine virus selection due to frequent changes in the viruses and difficulties in generating optimal candidate vaccine viruses for use in manufacturing,” the CDC stated in explaining the delay.9

The H3N2 vaccine component in this season’s vaccine is A/Kansas/14/2017. The CDC also added a new H1N1 strain, A/Brisbane/02/2018. Both B/Victoria and B/Yamagata virus components from the 2018-2019 flu vaccine remain the same for the 2019-2020 flu vaccine.


  1. Campbell AP, Ogokeh CE, McGowan C, et al. Influenza vaccine effectiveness against laboratory-confirmed influenza in children hospitalized with respiratory illness in the United States, 2016-17 and 2017-18 seasons. Abstract 899. IDWeek 2019. Washington, DC, Oct. 2-6, 2019.
  2. Garg S, Beacham L, Arriola C. Influenza vaccination reduces risk of severe outcomes among adults hospitalized with influenza A(H1N1)pdm09, FluSurv-NET, 2013-2018. Abstract 898. IDWeek 2019. Washington, DC, Oct. 2-6, 2019.
  3. NFID. Attitudes about influenza and pneumococcal disease prevention. 2019. Available at: https://bitly/359CNSN. Accessed Oct. 17, 2019.
  4. IAC. Influenza vaccination honor roll. Available at:
  5. CDC. Influenza vaccination coverage among health care personnel — United States, 2017–18 influenza season. MMWR 2018;67;1050-1054.
  6. Kwong JC, Schwartz KL, Campitelli MA, et al. Acute myocardial infarction after laboratory-confirmed influenza infection. N Engl J Med 2018;378:345-353.
  7. Hviid A, Hansen JV, Frisch M, et al. Measles, mumps, rubella vaccination and autism: A nationwide cohort study. Ann Intern Med 2019;170:513-520.
  8. CDC. Seasonal flu vaccine effectiveness studies. Available at: Accessed Oct. 17, 2019.
  9. CDC. Frequently asked influenza (flu) questions: 2019-2020 season. Available at: Accessed Oct. 17, 2019.