You’ve likely already heard the news: the flu is pretty bad this year, with the Centers for Disease Control (CDC) confirming a higher than usual level of illnesses, hospitalizations, and even deaths.
You also probably know that older adults (and certain other groups of people) have a higher risk of falling very ill from the flu, and have the highest death rates from flu.
But what many people don’t know is this: influenza is easily — and often — missed in older adults.
What do I mean by missed? I mean:
- Older adults (or their family members) may not realize an older person has the flu, because many older people don’t develop “typical” influenza symptoms.
- Health professionals often fail to test older people for influenza, even when they are sick enough to be hospitalized. This phenomenon was confirmed in a recently published study.
This is a very serious issue, especially when the flu virus is causing a lot of severe illness, as it is now.
The main problem is this: delayed — or entirely missed — recognition of influenza means that older adults often don’t get treated early — or at all — with anti-influenza drugs such as oseltamivir (brand name Tamiflu).
Particularly for those older adults who have chronic illnesses (especially those affecting the heart or lungs) or are frail, you don’t want to miss that chance to take anti-influenza drugs. They can’t guarantee an older person will avoid a hospitalization or death from influenza, but they do improve one’s chances.
And anti-influenza drugs are most likely to work when they are given within 48 hours of a person falling ill from influenza, with earlier being better.
So when flu activity is widespread, families need to be prepared to recognize potential flu.
And, you should be prepared for the possibility that the health providers might not think to test for influenza, unless you ask about it.
This article will help you learn to do these things. Here’s what I’ll cover:
- What are the usual symptoms of “influenza-like illness”
- Common symptoms of influenza in older adults
- Why older adults may not show typical influenza symptoms
- What we know about older adults & influenza testing
- What the CDC currently recommends, regarding influenza diagnosis and treatment
- What to do, if an older person falls ill during influenza season
You may also want to see this related article, which explains some influenza basics in more detail: Flu Shots for Older Adults: What to Know & Do.
And in case you are wondering: if you have not yet been vaccinated for the flu this season, it’s not too late. The flu is often active well into the spring (e.g. March, April, or even sometimes May). As I note in the article on flu shots, older adults will probably get better protection from the vaccine if they get the high-dose flu shot. Use VaccineFinder.org to find a flu vaccine near you.
Now let’s go into how you can recognize the flu in an older person.
What are the usual symptoms of influenza?
Here’s how the CDC defines “influenza-like illness”:
- Fever, meaning a temperature of 100°F (37.8°C) or greater, and
- Cough and/or sore throat, and
- No other known cause for the symptoms
It’s important to realize that these symptoms, on their own, are “non-specific,” meaning they can easily be caused by an illness other than influenza (such as a bad cold virus, strep throat, or even a bacterial pneumonia).
For this reason, health providers may decide to test a person for influenza, especially the test result might affect the decision to treat with anti-viral medication, or might help contain an outbreak.
“Uncomplicated” influenza is also often associated with other symptoms. The most common ones are nasal congestion and body aches.
Symptoms of influenza in older adults
Many older adults do develop typical symptoms when they fall ill from influenza.
But it’s also quite common for older adults to be sick from the flu and not have fever, cough, or sore throat.
Instead, older adults with the flu often experience the following problems due to influenza:
- Common non-specific signs of illness in aging adults. These include symptoms such as:
- “Dizziness” (a term people often use when they are feeling weak or if they get light-headed when standing)
- Loss of appetite
- Confusion or worse-than-usual mental function (this is called delirium)
- Malaise (which basically means feeling blah or unwell)
- An exacerbation (meaning a worsening) of a chronic heart or lung condition. Examples include:
- An exacerbation of chronic obstructive pulmonary disease, which often means increased shortness of breath, wheezing, and/or increased sputum production
- An episode of worsening heart failure, which often means shortness of breath and/or increased leg swelling
- A worsening of asthma symptoms
In a recently published study on influenza testing in older adults, during flu season, researchers independently tested all adults hospitalized with any type of respiratory diagnosis or shortness of breath for influenza.
They found that: “Among patients with study-confirmed influenza, ‘influenza-like illness’ was also less common in older patients (74% ≥ 65 years; 83% 50-64 years; and 81% 18-49 years).”
In other words, in this real-world study, 26% of hospitalized older adults with proven influenza did not have the typical “influenza-like illness” symptoms of fever plus cough or sore throat.
Why older adults may not show typical influenza symptoms
Here’s a core concept in geriatrics: as people age, they become less likely to have “typical” symptoms when they develop infections and some other types of illnesses.
This is due to two common issues that come up as people age: the aging of the immune system and decreased “physiologic reserve.”
Aging of the immune system
Aging is known to eventually bring on changes to the immune system. Since many common symptoms of illness actually reflect the immune system’s response to an infection, a less vigorous immune system will tend to generate less prominent symptoms.
For instance, fever is a very classic sign that the immune system is at work fighting infection. However, studies have found that older adults are less likely to have fever when they are ill with influenza.
Decreased “physiologic reserve”
The human body is designed to maintain stability and the ability to carry out key functions, even in the presence of stress or illness. This is why even if one is sick, one can usually stand up, think straight, and key organs keep functioning adequately.
To maintain this stability, the body relies on an intricate system of detecting problems and working to correct them quickly. So for instance, if your blood pressure drops, your heart will speed up to help maintain adequate blood flow throughout the body.
The body’s organs are also usually designed to have “extra capacity,” meaning that they usually don’t have to work at their maximum ability, to do their job reasonably well. So your brain usually doesn’t need to have all its neurons active and working well to do the thinking required, and your kidneys are able to keep your blood adequately filtered even if they lose some of their filtering ability.
At its peak resilience and effectiveness (usually when you’re in your mid-twenties), the body has lots of capacity to effectively respond to stressors. All your organs have lots of capacity, and the body’s systems for coordinating and correcting things when there’s a problem work well.
This is called having a lot of “physiologic reserve.” So although it’s possible for a young person to become delirious — or unable to stand — due to illness, it usually takes a very severe illness to do this.
But alas, as we get older, most organs develop some wear or damage, due to aging or chronic diseases. So they don’t have quite as much extra capacity as they used to. And so all those systems for maintaining stability and function in the face of illness become less effective.
Different older adults of the exact same age can have different levels of physiologic reserve; it depends on the person and their state of health.
Still, the overall trend is the same for everyone: as we get older, our bodies and minds become less resilient. Hence when an illness makes us sick and stresses our body, some older adults will show signs of things going a bit “haywire,” rather than just showing the very typical symptoms caused by the illness or our immune response to the illness.
Many of those non-specific signs of illness in older adults — especially weakness and delirium — are caused by having decreased physiologic reserve. Developing a worsening of heart or lung problems also reflects decreased reserve. They are basically signs of the body starting to malfunction because an illness stressor has come up and the body’s systems for maintaining overall function and stability can’t quite keep up.
What we know about older adults & influenza testing
It’s not exactly news or a recent scientific breakthrough, that older adults often exhibit vague symptoms when ill with influenza. And just about every clinician knows that most of the hospitalizations and deaths related to influenza occur in older adults.
Despite this, research has found that clinicians sometimes fail to order influenza testing for sick older adults.
Here is the conclusion of the study published in January 2018 that I have been referencing:
“Adults 65 years and older hospitalized with fever or respiratory symptoms during influenza season are less likely to have a provider-ordered influenza test than younger adults.
Some, but not all, of this disparity is due to a lower likelihood of influenza-like illness presentation.”
What the CDC currently recommends, regarding influenza diagnosis and treatment
Since we’re in the midst of a particularly bad flu year, this past December the CDC issued a special health advisory on the diagnosis and treatment of influenza. (You can read it here.)
Tellingly, the advisory notes that it’s being issued for the following reasons:
- To “remind clinicians that influenza should be high on their list of possible diagnoses for ill patients because influenza activity is increasing nationwide.”
- To “advise clinicians that all hospitalized patients and all high-risk patients (either hospitalized or outpatient) with suspected influenza should be treated as soon as possible with a neuraminidase inhibitor antiviral.” (Emphasis mine.)
Here are some other important points made in the advisory:
- “Evidence from previous influenza seasons suggests that antivirals are underutilized in outpatients and hospitalized patients with influenza who are recommended for treatment.”
- In other words, in the past doctors have often failed to offer antiviral influenza treatment to patients who should’ve gotten it, per the CDC’s recommendations.
- “All hospitalized, severely ill, and high-risk patients with suspected or confirmed influenza should be treated with antivirals.”
- The CDC notes that high-risk individuals who aren’t hospitalized should be offered treatment.
- Adults aged 65 and older are listed as “high-risk,” as are people with chronic pulmonary, cardiovascular, or kidney disease.
- “Antiviral treatment should be started as soon as possible after illness onset and should not be delayed even for a few hours to wait for the results of testing.”
- The CDC notes that “clinical benefit is greatest when antiviral treatment is administered as early as possible after illness onset.”
- Treatment should be started within 48 hours of illness onset. However, the CDC notes that starting treatment after 48 hours may still be beneficial for some people.
- “A history of current season influenza vaccination does not exclude a diagnosis of influenza.”
- The CDC estimates that this year’s seasonal flu vaccine is probably 30% effective against the particular strain of influenza A (H3N2) which seems to be causing most of the severe illness. So a person who has been vaccinated can still become quite sick from the flu.
- “During influenza season especially, high-risk patients should be advised to call their provider promptly if they have symptoms of influenza.”
- The CDC notes that providers may want to provide special phone lines to enable high-risk patients to discuss their symptoms by phone, and says that providers may want to consider providing a prescription for antivirals prior to an office visit.
The CDC advisory also includes a section on different types of influenza tests, and the CDC has a detailed page for clinicians here.
Now about those influenza tests. Probably the most important thing you should know about influenza tests is that they are not created equal, and some of them are known to have a significant “false negative” rate.
Meaning, certain influenza tests are known to have a non-negligible chance of missing people who actually are infected with influenza. (A test can also be falsely negative if the nasal swab is incorrectly done.)
The more accurate influenza tests are “molecular assays,” which test for the actual presence of viral proteins in a person’s nasal secretions.
However, it’s fairly common for healthcare providers to use an older (and cheaper) “rapid influenza diagnostic test (RIDT),” which provides a quick answer but is less accurate, and has a higher false negative rate.
Since the CDC is aware that some commonly used tests can miss influenza, the recent influenza advisory states: “Clinicians should be aware that a negative RIDT result does not exclude a diagnosis of influenza in a patient with suspected influenza when there is influenza activity in the community.”
What to do, if an older person falls ill during influenza season
I have shared a lot of information so far, so let me now try to boil it down to a few key take-aways. I will then share my top suggestions on what to do, for older adults who fall ill during flu season.
- When the flu is widespread, clinicians and families should be quick to suspect that a sick older person might have the flu, even if he or she doesn’t have a fever, a cough, a sore throat, body aches, or any of the other “typical” flu symptoms.
- In an older person, feeling weak or confused may be the only sign of having the flu.
- Influenza can become a life-threatening illness in older adults and other high-risk groups of people. Prompt recognition of possible influenza and prompt treatment with anti-influenza medication is key to reducing the chance of serious illness and death.
- Anti-influenza medications are most effective when started as soon as possible after the onset of illness, and preferably within 48 hours.
- Per the CDC, treatment should not be delayed while waiting for the result of an influenza test.
- The CDC also notes that the “rapid influenza diagnostic test” is not always accurate, and should not be used to rule out the flu if there has been a lot of influenza activity in the area.
- Research suggests that some health care providers may fail to recognize or test for influenza in older adults.
My recommendations on what to do:
- When the flu is widespread, be quick to suspect that a sick older person might have the flu.
- Remember that older adults can get quite sick from the flu even if they don’t have a fever, a cough, a sore throat, body aches, or any of the other “typical” flu symptoms.
- A worsening of a chronic heart or lung condition (especially COPD or heart failure) can be caused by influenza.
- Don’t delay in seeking medical attention, and in asking about anti-virals for influenza.
- Be proactive about asking for influenza testing and anti-virals while any test results are pending.
- Don’t expect the doctors to check for influenza or offer anti-virals. Many will, but some won’t.
- If a rapid influenza test is negative in an older person who is quite sick or has typical flu symptoms, ask about getting a more accurate test done.
Hopefully, the doctors will appreciate your proactive approach and how well-informed you are.
But I’ll be honest with you: you may have to be persistent, especially if the doctor waves off your concern or questions about influenza. (Or worse yet, if they say something like “What medical school did YOU go to?” when you ask extra questions.)
It’s not right that patients and families get pushback, especially when they are asking for care that is in line with guidance from the CDC or another relevant expert group. But it does happen 🙁
I hope this won’t happen to you, but if you think it might, then consider bringing in a copy of the CDC’s recent advisory. And remember, it’s always best to be as polite and appreciative as possible, when persisting and asking health providers to do a little more.
With the help of informed and proactive families, we can help more older adults get the care they need, and so reduce serious illnesses and deaths from the flu.
Questions? Comments? Post them below!
[Many thanks to Bob Barnett of Bottom Line Health, Inc., for alerting me to the recently published article on influenza testing in hospitalized adults.]
Ellen Tripp says
My 76 yr old friend had a bad reaction to Tamiflu (nausea and dizziness I think) and she said the list of possible side effects for the drug is scary. Makes me hesitant to ask for it if needed…
Leslie Kernisan, MD MPH says
Yes, nausea and even vomiting is a known side-effect of Tamiflu, and can affect 10-15% of people. So there is a risk of uncomfortable or distressing side-effects in taking these medications, but the issue should be short-term.
However research suggests that in previous pandemic years, among high-risk people, anti-influenza medications reduced the risk of hospitalization by 62%, and among people sick enough to be hospitalized, medication reduced mortality by 25-62% (with earlier treatment providing more risk reduction).
Neuraminidase inhibitors: who, when, where?
For those older adults (and other high-risk individuals) hesitant to take the medication, it is still a good idea to get promptly evaluated for potential flu. Although the CDC recommends not waiting for the results of an influenza test, a patient could decide to accept a slightly higher risk of having influenza and developing complications, in exchange for waiting for the results of an influenza test and then deciding whether or not to take the medication.
For others desiring more information regarding the benefit of anti-influenza drugs, see here:
Infectious Disease Society of America statement on Neuraminidase inhibitors
Very informative! My mother is 95 years old & was around family members who a couple of days later came down with the flu. Her geriatrician put her on a protective dosage of Tamiflu (only 1 a day instead of 2) as a precaution. She never developed symptoms, but I really appreciated this proactive measure!
Leslie Kernisan, MD MPH says
Yes, it may be considered reasonable to provide prophylactic treatment (it’s technically called “chemoprophylaxis”) to certain high-risk people who have been likely exposed to influenza by a household contact or by fellow residents in a facility. The CDC provides guidance here:
Influenza Antiviral Medications: Summary for Clinicians.
I’m glad your 95 year old mother is doing ok!
Very useful tips. My mother was diagnosed flu A a few years ago when she was 78 and she was prescribed Tamiflu when staying in the public hospital (in Hong Kong). However she developed confusion and delirium (and was diagnosed mild dementia later) when she was staying in the hospital. Last year when visiting a geriatrician, he said Tamiflu would worsen her condition. Not sure if he referred to her dementia when he said “her condition”.
A few weeks ago, my dad, my mom and I, living together, all got fever and cough. My mom and I had fever at 102°F and my dad was a bit lower. Our family doctor diagnosed that we all got flu by his clinical experience and without doing any test. I am quite sure that most family doctors in Hong Kong do not provide such test. Our doctor prescribed some drugs addressing fever, cough, sputum and running nose etc. He also prescribed antibiotics. But is it necessary to take antibiotics in this case? It is criticized that antibiotics are unnecessarily used (misused) nowadays. In my mom’s case, after two rounds of antibiotics (3 days for each round), she lost appetite and energy, which is not good for her as a dementia patient. Fortunately, she is getting better (but rather slowly).
Leslie Kernisan, MD MPH says
Thank you for sharing your story.
Antibiotics do not treat viruses. Now, influenza and other upper respiratory viruses are sometimes associated with a related bacterial pneumonia. If a person does show signs of pneumonia (and it usually takes an x-ray to distinguish true pneumonia from bronchitis), it can be hard to tell if the pneumonia is due to influenza or bacteria. So especially if a person is in the hospital or dangerously ill, it can be reasonable to treat with antibiotics just in case there is a bacterial component.
Otherwise, research generally indicates antibiotics are overused for upper respiratory infections (including bronchitis), most of which are viral and don’t benefit from antibiotics. For more, see: Antibiotics: When you need them—and when you don’t
So, I think you are right to question the antibiotic prescription. Many clinicians are used to prescribing them in part because patients have often demanded them. So the doctor might appreciate your asking if they are really necessary, and what is the indication.
Jim Sharp says
Excellent article. Hopefully lots of physicians and patients will see this info. Thanks for sharing.
Leslie Kernisan, MD MPH says
Glad you find it helpful!
Another very interesting and helpful article, Leslie; thank you. When my 83-year-old mother had flu recently, one of her symptoms was severe vomiting and diarrhea — she literally could not process any food or water (as it seemed to us) and so ended up dehydrated. Fortunately time on a drip in hospital got her rehydrated again. I have heard (on a post on the Elder Orphans website) other elderly folk report severe vomiting and diarrhea as symptoms of recently-experienced flu. Yet your article makes no mention of this. Could we have been misdiagnosing, then, and might this have been the noro virus?! Several weeks later,my Mum is still weak and tires very easily, but she’s slowly getting better.
Leslie Kernisan, MD MPH says
I have heard of influenza being associated with vomiting or diarrhea in children but not in older adults, and cannot find much mention of this in the scholarly literature. According to the UptoDate.com chapter on seasonal influenza: “Gastrointestinal illness, such as vomiting and diarrhea, are usually not part of influenza infections in adults but can occur in 10 to 20 percent of influenza infections in children.”
Gastrointestinal symptoms are, however, a known side-effect of anti-influenza medications such as Tamiflu.
You are right that norovirus is a common viral cause of gastroenteritis, and that is more what I’d be thinking of — along with other common causes of acute gastrointestinal symptoms — if an older person were to have vomiting and diarrhea. I would not attribute those symptoms to the flu unless it was going around and there was a positive test.
I suppose it’s possible to have both influenza and norovirus in quick succession or simultaneously, but have no idea how often it actually happens.
I’m glad your mother is better and hope she continues to recover.
My 65 year old mother went to the emergency room with nausea and vomiting, she tested positive for flu. While uncommon I think this is just the way some older adults bodies react to the flu.
Leslie Kernisan, MD MPH says
So sorry to hear about your mother. Nausea and vomiting due to influenza is more common in children, but I suppose it’s possible for it to happen with adults too. I hope she recovers soon.
Kathleen E Sander says
What about the articles I’ve read lately about the flu shot being so dangerous to older people, like myself ( I’m 78) Last year when I HAD one, i got terribly sick and even developed Pneumonia, it took a couple of months before I felt better. So there’s no way I’m going to subject myself to that again, being as I have a very weak immune system from all the allergies I have.
Leslie Kernisan, MD MPH says
I address the risks and side-effects of the flu shot in the related article, Flu Shots for Older Adults: What to Know & Do.
The expert consensus is that the flu shot is not dangerous to older adults, even though some people do get soreness or feel unwell for a few days after getting vaccinated. The CDC especially recommends that people with weak immune systems be vaccinated and otherwise protect themselves from the flu, because they are the ones most likely to develop serious illnesses and complications from the flu.
Of course, if you feel the flu shot really doesn’t agree with you, it’s not unreasonable to decline it, but it’s good to be aware that from the CDC’s perspective, there is no serious scientific evidence yet that the flu shot is “dangerous to older people.” For each individual person, the absolute likelihood of avoiding serious illness due to the flu shot is not very big. You can focus on other ways to avoid exposure to influenza virus (ask family to be vaccinated, wear a mask around people who might have the flu, etc). And of course, if you get symptoms that might be the flu, seek medical care early.
Alicia Butcher Ehrhardt says
I had the flu. I’m 68. I have a flu shot every year. But I also have CFS – and by the time I realized my symptoms were flu, and not ‘the usual’ I live with, I was well past the window for taking antivirals. I’d never had the flu before – and didn’t realize the temperature swings were worse than usual, and loss of appetite was a good indicator.
I credit the shot with minimizing the effects, but it took me a long time to get over the whole thing (3 weeks), and it raised my BP and my heart rate went from a normoal 66 to 100 for several days (very uncomfortable if you’re not used to it).
I only mention the above because, due to the chronic illness, I overreact to every medication I try, and probably would have had all the extra side effects. It’s a tightrope – plus going to the doctor or urgent care when all I wanted was to rest more than usual (and stay hydrated) wastes so much energy. Older patients with weak immune systems such as I am also tend to pick things up easier – I got mine by accompanying my husband to an eye doctor appointment because he wanted a second pair of ears.
Leslie Kernisan, MD MPH says
Things are definitely challenging if one is particularly sensitive to medications. Good luck with the “tightrope”!
shangkar ganesh chandiram says
Dear Doctor Leslie,
my mother about 60 years old. for the past 4 years she have non stop flu. even she took medication but it only cure for sometimes and after certain period she started keep snizzing. sometimes more 3 hangerchief get wet per a day.
she cannot stand with cold or car air cond. even sometimes the doctor inject her also still the problem persist. she is diabetic person at glucose level at 9. she also taking BP tablets and other pain killer for her knee problem.
what is the test suitable for her? pls advise. Thanks.
Leslie Kernisan, MD MPH says
So, it’s not possible to have the flu non-stop for 4 years. Since you mention sneezing and handkerchiefs, I’m guessing you mean that she’s had some kind of nasal congestion symptoms for a while.
Unfortunately, it’s not possible for me to know what might be causing this. I would recommend asking her doctors to explain what they think is causing her symptoms; can’t imagine they think it’s due to influenza. You could also consider getting a second opinion or consulting a specialist, perhaps one specialized in otolaryngology (the “ears, nose, throat” specialists). It might be something related to her nose or sinuses or perhaps even allergies. Good luck!
LINDA LEVINE says
I am 75 I have had flu like symptoms for 3 weeks . I live alone and care for myself. I am on infusions of Remicade for Crohn’s Disease which makes my immune system more compromised. I went to my GP 1 weeks ago and she put me on a puffer and antibiotics tablets for five days.No follow-up appointment was given. It didn’t help and I was feeling progressively worse . I stayed in bed and talked to no one yesterday since talking seemed to worsen my cough. I slept off and on for 24 hours. My weight has dropped several pounds. We are still waiting for the extra strong flu shot here in Toronto….meanwhile this is my second bout of the flu….I am getting very little satisfaction from my doctor so as much as I don’t want to be sitting in the emerg. dept. of a hospital, as I fear more flu exposure, I feel I have no other option…When your a senior I have found doctors don’t seem to care as much as they figure you’re old anyway….
Leslie Kernisan, MD MPH says
Sorry that you’ve been feeling unwell. Your symptoms do sound worrisome, so it’s too bad that you don’t feel satisfied with your doctors.
One thing that sometimes helps people in your situation is to recruit a friend or family member to be your “medical companion” and accompany you to your doctor’s visits. This does mean a little less privacy but it can be a huge help to have an extra set of eyes and ears in the visit. Some people also hire professional patient advocates to accompany them and advocate for them.
Hope things get better for you soon and that you find a way to get the care you need from your health providers.
Jason J Chen says
I am 62, catching cold much less often than decades ago. Not sure whether it’s due to reduced immune response or increased specific immune response. I like your article. Best, Jason
Nicole Didyk, MD says
Hi Jason, and I’m so glad you like the article. Glad to hear you are staying well, whatever the reason.
Rachel (do not print last name) says
I am turning 70 in 2 months. I am in good health. I took the flu shot, but I came down with the flu anyway. I have strep at the same time. I’m on amoxicillin, anti-nausea, tamiflu. tylenol…My fever has been 103+. Nausea, swollen glands, severe body aches, palpitations, lots of pus in my throat, diziness, absolutely no appetite…I have never been so sick in my life. I went to an urgent center yeaterday because I couldn’t take it any more.I take the flu shot every year and never got the flu. And I heard that if you do come down with the flu even though you had the shot, it will be a milder case. No! That’s not what happened!
Nicole Didyk, MD says
Hi Rachel, I am so sorry to hear about your illness. Unfortunately, the flu shot doesn’t work 100% of the time (more like 40-60% in older adults). Here is an article about the flu shot that you may find interesting.
Mary A Albrecht says
Husband is 93…..tested positive for A flu at minute clinic a week ago today. Started on Tamiflu which ended yesterday. He had had flu vaccine this fall and also has had pneumonia shots in previous years.
No overt symptoms but major fatigue which seems more today that yesterday. Comments?
Nicole Didyk, MD says
Hi Mary. Sorry to hear that your husband is not feeling well. As Dr K explains, the flu vaccine is not 100% effective at preventing the flu, so unfortunately, a number of individuals who get the shot will still get the flu.
The flu is a serious illness which can lead to complications like pneumonia, deconditioning (from having a lower activity level while feeling unwell) and dehydration. If a person is not feeling better after the flu has run its course, it may be reasonable to see the doctor again to rule out these issues.