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From Johns Hopkins Bloomberg School 11/4/26
What to Know About Flu, COVID-19, and RSV This Fall
Influenza activity is increasing, while RSV and COVID case numbers remain low.
By Morgan Coulson
As we head into the late fall and winter months, flu cases are beginning to rise in parts of the U.S., even as overall respiratory virus activity remains low. The CDC is predicting a relatively moderate respiratory virus season, similar to last year’s, when weekly hospitalizations from flu, COVID-19, and RSV peaked at around 16 per 100,000 people.
But that’s no reason to put off vaccination, explains Andrew Pekosz, PhD, a professor in Molecular Microbiology and Immunology: “This is a good last call to get your influenza vaccination for this year, because vaccines work best when taken before the influenza season starts.”
This season also brings a new option for some adults: a recently approved mRNA influenza vaccine for people ages 50 and older.
“The hope is that the new mRNA vaccine will produce a better immune response against influenza and, therefore, provide better protection,” says Anna Durbin, MD, a professor in International Health and director of the Center for Immunization Research.
In this Q&A, adapted from an October 29 media briefing, Pekosz and Durbin discuss emerging respiratory virus trends, what we know about this season’s vaccines, and how people can protect themselves and others as the season progresses.
What is the current situation with influenza in the United States?
Andrew Pekosz: Influenza activity is low but increasing, particularly in the western and southern U.S. This is early, but not unheard of. The cases seem to be driven by a variant of the H1N1 influenza virus, which has some new mutations compared with last year’s H1N1 virus. Those mutations allow it to escape some of the immunity in the population. However, data suggest this year’s influenza vaccine can recognize this variant.
Influenza vaccines cover three different viruses, and usually different influenza viruses cause infections at the beginning and end of the flu season. So, even if you hear about a potential mismatch with the H1N1 component, it’s important to get the vaccine because the other two components look like they’re going to be pretty good matches for the viruses emerging early in the flu season.
How well do this season’s COVID and RSV vaccines match the strains circulating now?
AP: For COVID, we’re seeing low but steady activity. We expect another increase in cases sometime in December or January.
We haven’t seen much RSV activity this year, which is somewhat unusual. However, I expect we’ll begin seeing RSV cases in the next couple of weeks.
Now is the time to get your COVID and RSV vaccines, if you’re eligible, along with influenza and pneumococcal vaccines, to prepare for the respiratory virus season. Both the COVID and RSV vaccines are very good matches for the viruses currently circulating.
The RSV vaccine is recommended for a more limited group of individuals, particularly those ages 75 and older, as well as people with certain underlying conditions or who are immunocompromised. That vaccine has demonstrated very good efficacy over the past few years. [Note: The RSV vaccine is not currently an annual vaccine, per the CDC.]
What’s the difference between the new mRNA flu vaccine and the traditional vaccine?
Anna Durbin: Essentially, the mRNA vaccine enters your cells and instructs them to make the flu protein against which your body produces antibodies. The cells make that protein and then present it to your immune system, exposing the immune system to the protein, or antigen.
Current traditional flu vaccines, by contrast, contain proteins that stimulate an immune response. Unlike mRNA vaccines, they don’t enter the cells in the same way to stimulate the broadest possible immune response. Traditional vaccines generate a good antibody response but may not stimulate other parts of the immune system as effectively as mRNA vaccines do.
Which is more effective?
AD: We don’t have data from the current flu season yet. However, the clinical trials used to support the mRNA vaccine’s approval showed that, in people ages 50 and older, it performed better than traditional vaccines.
One important consideration is that adults ages 65 and older receive a higher dose of the traditional flu vaccines than younger people. The mRNA vaccine was not directly compared in clinical trials with those high-dose vaccines in people ages 65 and older. However, we know that the antibody responses generated by the mRNA flu vaccine in people ages 65 and older were at least as good as those generated by traditional flu vaccines.
Until we get good real-world efficacy data from the flu season, we won’t know for sure.
How is the mRNA vaccine different from a public health standpoint?
AD: The advantage of an mRNA influenza vaccine is that it can be produced very quickly. For instance, if a new strain emerges over the summer, the [fall] vaccine [for that year] could potentially be changed to match it.
Right now, the FDA holds a meeting every March to select which strains will be included in the influenza vaccine. That meeting happens so early because it takes a long time to produce traditional influenza vaccines.
The hope with an mRNA vaccine is that we might be able to hold another meeting in July or August and update the vaccine if the circulating strains have changed.
We’re not there yet. The agency is discussing and exploring that possibility, and I think a lot will depend on the evidence generated by this new mRNA influenza vaccine.
How can a person tell whether they have the flu, COVID, a cold, or something else?
AP: Usually, you can distinguish a cold from something more significant or serious by the effect it has on your ability to breathe and by the severity of your cough. If you have difficulty breathing, that can mean the infection is spreading deeper into your lungs. In that case, it may not be a common cold but one of the other respiratory viruses.
There are some useful at-home testing kits that can help determine whether you're infected with influenza, RSV, or COVID-19. Knowing which virus you have is particularly important if you’re in a high-risk group for severe illness.
Antiviral treatments are available for influenza and COVID-19, and they have been shown to reduce the duration of symptoms and the likelihood of developing severe illness. The key is that you need to start these antivirals soon after symptoms begin.
Be proactive. Keep some at-home tests available, and if you test positive for one of these viruses, contact your pharmacy to make sure you can get the appropriate antiviral medication and begin taking it as soon as possible.
What should immunocompromised people and adults ages 65 and older do this fall?
AD: Immunocompromised people and adults older than 65 should get vaccinated.
We also know from many studies that adults over 65 often get infected by their grandchildren and other children. Get young children vaccinated against influenza, not only for older adults’ protection but also because influenza can cause serious complications in children, including death.
How long after vaccination does it take for protection to develop?
AP: It takes about two weeks for influenza vaccine protection to reach its maximum level. That protection then lasts for several weeks to several months after vaccination.
Getting vaccinated before influenza becomes widespread will provide the greatest protection against disease.
What is the most important thing for primary care physicians to know about this flu season?
AD: Influenza can be a very serious illness. The CDC reported almost 5,000 laboratory-confirmed influenza hospitalizations nationwide during the week ending October 17. This is the highest early-season hospitalization rate for mid-October since the 2010–2011 flu season. [The following week, ending October 24, that number rose to 6,100 hospitalizations nationwide, according to the CDC.]
I think it’s really important, particularly for older adults who are at greater risk of severe influenza, to get vaccinated.
What I tell my patients, and what I encourage other physicians to tell their patients, is that a flu vaccine is the best way to protect yourself against influenza, and to get vaccinated as soon as possible.
Fewer people are getting the flu vaccine, or they are getting it later in the season. What is the impact of this?
AD: We do think that, overall, fewer people are getting vaccinated against various diseases, which increases the risk of infection. Unfortunately, when fewer people get vaccinated, influenza can spread more easily, resulting in more infections and potentially serious consequences for people’s health.
There are a lot of questions people have about vaccines, and there’s been a lot of misinformation circulating. I encourage people to talk with their physicians.
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