Flu is nothing if not unpredictable, thus the adage, “If you’ve seen one flu season, you’ve seen one flu season.”

On the one hand, public health officials are warning a possible severe influenza season is on the horizon, partly because COVID-19 shutdowns and precautions led to a historically low flu season in 2019-2020. On the other hand, Johns Hopkins epidemiologists reported a mild flu season in the Southern Hemisphere, which generally is predictive of a similar season for the Northern Hemisphere. But influenza is a mutable virus, and the vaccine sometimes does not match a strain that becomes predominant.

“It appears that the 2021 Southern Hemisphere influenza season was largely similar to 2020, which is an encouraging indication that the Northern Hemisphere could face a similar trend,” Johns Hopkins Outbreak Observatory reported. “But the circumstances, both in terms of COVID-19 epidemiology and protective measures, are not necessarily conducive to mitigating seasonal influenza transmission. It is critical that public health officials and healthcare systems effectively implement plans for slowing community transmission as much of the world’s already-limited health system capacity has been absorbed by the COVID-19 pandemic.”1

The problem with a historically mild flu season in 2019-2020 is so few people were infected they now have little residual immunity.

“When there is active flu one year to another, then we have more people — not just who are vaccinated — but people who were actually sick and have built up some protective immunity,” said Rochelle Walensky, MD, director of the CDC. “That immunity actually helps us, especially those who have not been vaccinated.”2

Another signal of more circulating flu virus in the 2021-2022 season is the early, unseasonal appearance of respiratory syncytial virus (RSV), she explained at an Oct. 7 press conference held by the National Foundation for Infectious Diseases (NFID).2

“We have had a large amount of RSV in the last couple of months, which is atypical for this seasonal virus,” Walensky said. “We did not see some of these respiratory viruses last year because we were taking those prevention and mitigation strategies [for COVID-19].”

CDC surveillance conducted at Vanderbilt University confirms this unusual emergence of RSV, said William Schaffner, MD, professor of preventive medicine at the school and medical director of the NFID.

“We have seen an unseasonal increase with RSV, and that’s continuing,” Schaffner said. “Is that a harbinger of a worse influenza season? We don’t know, but we certainly don’t want a ‘twindemic’ of both COVID and influenza. Let’s get vaccinated against both.”2

Flu Shots Mandated?

With mandated COVID-19 vaccination in healthcare settings now subject to a federal presidential order, there is some thought that more hospitals may mandate flu immunization. For example, the Johns Hopkins Hospital policy requires flu vaccination, but allows medical and religious exemptions, requiring “everyone who has not received the influenza vaccine [to] wear a mask within 6 feet of a patient during the flu season. The mask must be worn during the time period from Nov. 19, 2021, to May 15, 2022. Vaccinated staff will receive purple ID badge clip.”3

The CDC reported 80.6% of healthcare workers stated they took the flu vaccine during the 2019-2020 season, similar to immunization level the season prior. “Coverage was higher among healthcare personnel who were required by their employer to be vaccinated (94.4%) than among those whose employer did not require vaccination (69.6%),” the CDC noted.4

Flu vaccination has faced historical resistance from people who fear or simply refuse the shot, much as with the COVID-19 vaccines. For those who can overcome the misinformation and see the benefit is much greater than the risk, the shots for flu and SARS-CoV-2 can be given at the same time.

“We can give flu vaccine and COVID vaccine on the same visit,” said Patsy Stinchfield, RN, MS, CPNP, president-elect of NFID. “You don’t need to separate them, but usually we will administer them in separate arms.”2

In a recent NFID survey, 44% of U.S. adults said they are unsure or do not plan to take the flu vaccine during the 2021-2022 flu season.5 In another troubling finding, 23% of people at high risk of flu complications said they were not planning to take the vaccine. People at higher risk of flu complications include pregnant women, children age 5 years and under, those age 65 years and older, and those with chronic conditions such as diabetes, lung conditions, or heart disease. The CDC recommends everyone 6 months and older be vaccinated against influenza.

Those survey findings caused alarm, but “the pandemic does seem to be driving changes in some prevention behaviors,” Schaffner said. “For example, 54% of U.S. adults plan to wear a mask during flu season. Forty-five percent say the pandemic will make them more likely to stay home from work or school if they are sick. That’s good news.”

‘That Dog Won’t Hunt’

Reasons for not taking the vaccine included the age-old “I never get the flu,” and the vaccine is not effective. Another long-imploded myth came up after an unidentified reporter asked: “How do we really know the flu vaccine does not cause flu?”

“You cannot get flu from the flu vaccine. That’s an old myth — please, you can’t do that,” an exasperated Schaffner said. “Virtually all the vaccines are made up of only parts of the virus, so there is no way that they can recreate the virus in your body to give you influenza. [No one] can hide behind that as a reason not to get vaccinated. As we say in Tennessee, ‘That dog won’t hunt.’”

Since the discussion was breached by serious misinformation, Schaffner explained why the live, attenuated nasal spray vaccine also does not cause flu.

“It is a miracle of modern science that the virus can stimulate your immune system but it cannot get down into your chest,” he said. “It can’t multiply there. It’s ‘cold adapted,’ as we call it, and cannot multiply at the slightly higher temperatures down in your lungs. Even that live attenuated virus cannot give you the flu.”

Stinchfield said unequivocally, “It is not possible to get influenza from the flu vaccine.” She then added an artful analogy that vaccination is like practicing before a game or performance.

“When your kids are saying they don’t want to get the flu shot, tell them you practice for your sport, you practice for choir and band,” she said. “This is practice for your immune system. You give it a little bit of a vision ahead of time so when the real virus comes your way, your immune system is ready.”

The 2021-2022 influenza vaccine protects against four strains of flu, with immunity in place about two weeks after vaccination. However, the vaccine does not protect against other viruses.

“It is not uncommon during respiratory season that someone would get the flu vaccine and a week later get a cold,” Walensky said. “We need to make sure that people recognize that is not the flu vaccine.”

Regarding efficacy, the flu vaccine is made every year to match the circulating viral strains. Sometimes, it is more effective than others. However, even in an imperfect year, the flu vaccine can prevent hospitalization and death, Walensky said. For example, a record 199 children died of flu during the 2019-2020 season in the United States. “Consistent with findings from other seasons, about 80% of those children were unvaccinated,” she said.

Co-Infection with SARS-CoV-2

If flu returns in force, there also is a risk of co-infection with COVID-19, which could prompt a serious inflammatory immune response. The viruses can present with similar symptoms of fever, cough, and shortness of breath, but there are tests to discern between the two or identify a co-infection.

“I have seen a couple of cases who had both infections simultaneously,” Jamie Rutland, MD, CEO of West Coast Lung in Newport Beach, CA, said at the NFID conference. “Those individuals were taken care of at home, but when they presented to the ER, they were positive for influenza A and SARS-CoV-2. The inflammatory response of the immune system is going to be activated, which, quite frankly, is what we are all afraid of.”2

“It’s another reason to get vaccinated for both, and we may see more co-infections because there will be more flu this year,” Schaffner added.

Both influenza and SARS-CoV-2 are serious infections during pregnancy, so the safety of vaccines for both viruses was emphasized to protect mother and child. There also are effective antiviral treatments for influenza, and pregnant women were urged to contact their provider at the first sign of symptoms.

“It is really helpful to call early, because your oxygen level can’t go too low before it starts effecting the baby,” Laura Riley, MD, obstetrician and gynecologist-in-chief at NewYork-Presbyterian said at the NFID conference. “We want to know if you are having those symptoms, even if they seem mild. Most pregnant women we don’t even test. If we think it’s flu, we are going to give you medicine. That’s how serious we take it.”

The CDC has rigorous safety systems in place for both flu and SARS-CoV-2, which in terms of adverse events allows detection of “needles in haystacks when they occur,” Walensky said. “We have seen extraordinary safety with the flu and COVID vaccines in pregnancy.”

There is some thought the pandemic will change the way people respond to respiratory viruses, and measures like masking, social distancing, and avoiding crowded indoor settings will become more common in future flu seasons. Given the social division over COVID-19, all bets are off on people for the current flu season.

“There are probably two groups out there, one being the very careful who are following this thoughtfully,” Schaffner said. “The data from the NFID survey [indicate] that these people will put on masks and do a little more social distancing when they encounter influenza in their community. There are other folks, as we know, who are still pretty cavalier about influenza and probably won’t take those precautions.”

In addition to emphasizing vaccination for both viruses, the utility of masking and other mitigation measures will be a recurrent public health message, particularly for those at high risk of complications if infected with either — or both, Schaffner said.

REFERENCES

  1. Kaushal N. Southern Hemisphere seasonal influenza. Outbreak Observatory, John Hopkins Bloomberg School of Public Health. Sept. 16, 2021.
  2. National Foundation for Infectious Diseases. 2021 NFID influenza/pneumococcal disease news conference. Oct. 7, 2021.
  3. Johns Hopkins Medicine. Johns Hopkins 2021-22 flu campaign. 2021.
  4. Centers for Disease Control and Prevention. Influenza vaccination coverage among health care personnel — United States, 2019-20 influenza season. Reviewed Oct. 1, 2020.
  5. National Foundation for Infectious Diseases. 2021 national survey: Attitudes about influenza, pneumococcal disease, and COVID-19. October 2021.