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Whenever a nip of cold is in the air, and coughs and sneezes ring out in public places, you know it’s flu season again. If you live with diabetes, you’re probably being prodded to go get a flu shot and related vaccines.

People with diabetes (PWDs) face a higher risk of severe illness any infection, including influenza. That’s why it is so important that those with diabetes get their flu shot each season — especially during pandemic times when COVID-19 remains a public health threat in particular for people with chronic conditions.

This article will explain more about why PWDs should consider the flu shot each season, when the best time for that vaccination may be, and what possible impacts it may have on blood sugars and diabetes management.

The Centers for Disease Control and Prevention (CDC) recommends that everyone with diabetes get a flu shot. This includes type 1 and type 2 diabetes, LADA (latent autoimmune diagnosis in adults), and gestational diabetes during pregnancy.

Likewise, the American Diabetes Association (ADA) also recommends annual flu shots for all PWDs and their families, as do the other diabetes organizations and medical professional groups.

Contracting the flu can weaken the immune system, leading to fluctuating and higher glucose levels — which puts PWDs at elevated risk for severe infection as well as a higher risk for COVID-19, and its effects on the body. Studies since 2020 have shown largely that PWDs are more likely — even 3 times more likely — to see more severe COVID-19 illness, compared to those without diabetes.

According to the CDC, about 30% of the adults hospitalized with flu in recent seasons lived with a type of diabetes. This 2017 study states that PWDs are at increased risk for developing severe complications from the flu, and this 2022 research points out that’s even more pronounced for adults 65 years and older who face more severe flu illness if they live with diabetes.

That is why a shot is recommended every year because there’s a different strain of flu circulating every year.

Defining influenza

Flu is a highly contagious respiratory illness caused by a family of quickly evolving influenza viruses.

What makes flu challenging is that it’s caused by a virus, making it difficult to treat. Diseases caused by bacteria can be treated more easily with antibiotics, but our antiviral tools are more limited. Truly, the best way to fight the flu is to avoid getting it in the first place.

Just before COVID-19 started, the CDC’s annual figures show an estimated 35 million flu illnesses during the 2019-2020 season. That includes 380,000 hospitalizations for the flu, 16 million related medical visits, and 20,000 flu-related deaths.

The 2021 season was unusually low because of COVID-19. Many people’s pandemic-related preventive measures (face masks, social distancing, different routines) helped lower flu rates. However, many public health experts and the CDC have warned that the 2022-2023 flu season could return with a vengeance.

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Marina Basina MD, an endocrinologist at Stanford Medlain, said it’s important for everyone with diabetes to get a flu shot because of the higher risk of severe illness and its implications on diabetes management.

“If a person with diabetes gets the flu, it becomes much more difficult to manage blood sugars,” she told Healthline. “Any infection will elevate blood sugars and increase variability in the readings and resistance to insulin.”

She added that flu symptoms can also lead to low blood sugars and dangerous diabetes ketoacidosis (DKA) even when blood sugars are not significantly elevated.

Timing may vary each season.

But the CDC points out that flu viruses are most common in the United States during the fall and winter months. Influenza activity often begins to increase in October and November. Most of the time, it peaks between December and February — though flu season can go into early May.

The CDC reported that the flu season from Oct. 1, 2018, to May 4, 2019, was actually the longest-stretching one in a decade at that time, starting strong early on before abating and then followed by another strain of flu kicking in later in the season.

Of course, with COVID-19, the 2020 and 2021 seasons saw unusually low flu rates because of the increased pandemic precautions and more people getting flu shots.

Many public health experts believe that the 2022-23 flu season will bring more cases of the flu than the United States has seen in recent years.

As background, there are several different types of influenza vaccine:

  • Inactivated influenza vaccine (IIV): This is considered the traditional flu shot, usually given as a shot in the upper arm.
  • Elderly flu shot: For the older crowd, there are high dose shots, as well as one formulated with an adjuvant, an ingredient that boosts the immune system response to the vaccine.
  • Recombinant flu vaccine: This vaccine has a short shelf life, so you’re not as likely to see it.
  • Nose-snort flu vaccine: It’s an alternative called LAIV, which stands for live attenuated influenza, approved for nonpregnant people 2 to 49 years old without certain underlying medical conditions. Diabetes isn’t specifically listed as one of those underlying conditions, although the list includes “people with weakened immune systems” — which certainly does include PWDs.
  • Xofluza: Approved by the FDA in the 2018-2019 flu season, this new medication was the first flu antiviral OK’d in almost 20 years. It’s for those 12 years and older who’ve only been showing flu-like symptoms for a maximum of 48 hours. For the 2019-20 flu season, the FDA expanded the indication for use of Xofluzo to those 12 years or older who are at high risk of developing flu-related complications, such as those with diabetes.

Despite all of the info above, the CDC advises that PWDs should get injectable dead-virus fluvaccinations, thanks to the “long-established safety record” for this kind of vaccination in people with diabetes.

It might.

Your arm often aches right after getting a flu shot, because that special vaccine liquid has gone right into your muscle. Until it’s fully absorbed, any kind of pain can cause your blood sugar to spike.

The body’s immune system may be reacting to the vaccine. This initial burst of immune system response causes inflammation from the antigen reaction, and that can trigger a blood sugar spike the same way illnesses do.

The flu can cause your body to release the stress hormones adrenalin or cortisol, which reduce the effectiveness of insulin, meaning you might see higher glucose levels as a result.

There is little actual research on how flu shots can lead to higher blood sugars.

According to the national vaccine safety monitoring database called the Vaccine Adverse Effect Reporting System, there have been more than 361 reports of hyperglycemia after a flu shot. This 2022 study included 34 adults with diabetes during the 2018 to 2020 flu seasons, examining their blood sugars in the first 24 hours after they’d gotten a flu shot. Higher blood sugars were found in the first day after the flu shot and returned to pre-vaccination levels by the second day.

Aside from that research, only one other case report highlights higher blood sugars after the flu shot. This 2018 research analysis article mentions a 41-year-old man with type 2 diabetes, who reported “feeling fatigued and groggy” within 2 hours of a flu shot and having a blood sugar of 264 milligrams per deciliter (mg/dL) about 6 hours later.

That person’s healthcare team could not pinpoint a specific reason for the glucose rise, nor did they indicate it was caused directly by the flu shot itself.

Analyzing that example, the study authors stated: “The purpose of this case report is to alert healthcare professionals about this potential effect, which is not described in vaccine package inserts or commonly used drug databases. We agree with the vaccination recommendations for people with diabetes and believe that the benefit outweighs the risk of transient, acute hyperglycemia. Patient knowledge and involvement remain the cornerstones of diabetes management. Therefore, it is important to educate patients and alleviate concerns that may arise during their routine (blood sugar management), while emphasizing the importance of vaccines.”

The study authors continued, “We do not recommend changes in pharmacotherapy or SMBG frequency after vaccination because such changes would place an unnecessary burden on patients. Our hope is that future research may shed more light on this phenomenon and enhance understanding vaccination in people with diabetes for both patients and healthcare professionals.”

If your blood sugars rise after a flu shot

This is what most diabetes doctors and endocrinologists advise relating to glucose level changes after a flu shot:

  • Correct any elevated blood sugars with fast-acting insulin or (for those using an insulin pump) an increased background basal rate.
  • Avoid increasing any long-acting blood sugar control medications, as there’s no predicting how long the elevated blood sugar from the flu shot might last.
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Both the flu and the common cold result from viruses, but the flu packs much more of a punch. You may have similar symptoms at times, but some are more distinct for the flu or a common cold.

Official flu symptoms may include:

  • body aches (these tend to be a key warning sign for most people that they have the flu, rather than a cold)
  • fever
  • cough
  • sore throat
  • runny or stuffy nose
  • headache
  • chills
  • fatigue
  • vomiting
  • diarrhea

Meanwhile, for a common cold, symptoms may include:

  • gradual onset of symptoms
  • sneezing
  • stuffy or runny nose
  • cough or chest discomfort
  • slight aches
  • fatigue or weakness
  • sore throat

Remember that any cold or illness striking someone with diabetes can cause your blood sugars to spike.

The result can be dangerous diabetes ketoacidosis (DKA), which can rise to the level of a medical emergency. Testing for ketones is important. This can be done using an at-home urine testing kit widely available at drug stores without a prescription.

For those who’ve not been diagnosed with diabetes, it’s also important to remember that flu-like symptoms frequently appear as a telltale sign of newly onset diabetes — especially type 1 diabetes. It can get deadly, very quickly. So make sure to know the warning signs of diabetes and be ready to handle this whether it’s actually the flu or not.

The CDC recommends getting the flu vaccine before flu begins spreading in your community. This is because it takes about 2 weeks after vaccination for the flu shot to start working in the body.

So it makes the most sense to get vaccinated early in fall before flu season kicks into full swing. Specifically, the CDC recommends that people get a flu vaccine by the end of October.

Some years, the flu may begin early and then ebb for a while before another strain kicks in. Getting vaccinated later, however, can still be beneficial and vaccination typically continues to be offered throughout flu season, even into January or later.

Children who need two doses of vaccine to be protected should start the vaccination process sooner because the two doses must be given at least 4 weeks apart.

You should still get a flu shot even if you’ve already experienced illness from influenza that season.

Because the vaccine protects against several “circulating” strains, it offers you protection against any other strains of flu you might get in the coming months. Without the shot, you could come down with another strain and be sick twice in a year.

If you do get sick, make sure you consult your doctor or healthcare team whether you’ve had a flu shot or not.

PWDs are candidates for antiviral drugs, which are most effective if started within 48 hours of the onset of symptoms. They won’t make you feel better overnight, but they can shorten the length of a bout of flu and greatly reduce the risk of serious complications.

Does the flu shot cause type 1 diabetes?

No, it does not. Scientists do not know what specifically causes type 1 diabetes (T1D), but there is no evidence that flu shots, nor any routine childhood immunizations to protect against other diseases (measles, polio, etc), cause this autoimmune condition. Here are just a handful of studies proving that lack of a link:

  • A 2016 meta-analysis of 23 previous studies found no link between routine vaccinations and an increased risk of developing T1D.
  • A 2021 study looking at medical data for more than 500,000 children in the United States found no connection between the recommended timing for childhood immunizations and the risk of developing T1D.
  • In Norway, a research group compared people younger than 30 who received the vaccine to protect against the “swine” flu with those who did not get the vaccine. The risk of T1D did not increase after being vaccinated.
  • A long-term study published in 2018 involved children in Sweden and Finland, who were identified as having a higher genetic risk for T1D. Researchers found no difference in that diabetes development between the kids who did and did not receive the vaccine for swine flu in 2009.

Can the flu or other illnesses trigger type 1 diabetes?

While researchers do not know what exactly causes T1D, major illnesses like the flu are believed to play a role in the development of this autoimmune condition. It doesn’t exactly “cause” the T1D, but speeds up the onset. Many researchers are studying the effects of viruses on T1D development, including whether COVID-19’s effects influence the onset of this autoimmune condition.

How does the flu shot help people with diabetes?

While the clear benefit of a flu shot is to protect against the flu, some research shows other benefits for people with diabetes who get this annual vaccine.

In this 2020 nationwide study involving more than 240,000 people with diabetes, the researchers determined that the influenza vaccination was tied to a reduced risk of heart attack, stroke, cardiovascular death, and death overall from all causes. In fact, the flu shot may improve overall health outcomes, including diabetes-related complications often heightened as a result of someone having the flu, the research concluded.

People with diabetes face a higher risk of severe illness from any infection, including influenza. That’s why it is so important that those with diabetes get their flu shot each season. The Centers for Disease Control and Prevention, along with all diabetes organizations, advise a flu shot each year, and it’s recommended for everyone by the end of October.