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Understanding primary immunodeficiency (PI)
Understanding PI
The more you understand about primary immunodeficiency (PI), the better you can live with the disease or support others in your life with PI. Learn more about PI, including the various diagnoses and treatment options.
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Living with PI
Living with PI
Living with primary immunodeficiency (PI) can be challenging, but you’re not alone—many people with PI lead full and active lives. With the right support and resources, you can, too.
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Get involved
Get involved
Be a hero for those with PI. Change lives by promoting primary immunodeficiency (PI) awareness and taking action in your community through advocacy, donating, volunteering, or fundraising.
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Advancing research and clinical care
Advancing research and clinical care
Whether you’re a clinician, researcher, or an individual with primary immunodeficiency (PI), IDF has resources to help you advance the field. Get details on surveys, grants, and clinical trials.
What is the flu?
Influenza, commonly known as "the flu," is a respiratory disease that usually comes on suddenly, with symptoms that vary from person to person. These symptoms may include aching muscles, sore throat, a dry cough, a runny or stuffy nose, fatigue, headache, a burning sensation in the chest, eye pain, sensitivity to light, and fever and/or chills (note that people with primary immunodeficiency (PI) may not spike a fever).
Although many people think of the flu as harmless, from 2010-2020, the U.S. Centers for Disease Control and Prevention (CDC) estimates that between 12,000-52,000 people died of flu-related complications each year.
Colds, COVID-19, and the flu have overlapping symptoms but are different respiratory illnesses with different treatments, so it’s important to be tested if you feel sick. Note that it is also possible to get multiple respiratory illnesses at the same time.
Does PI put you at high risk for flu complications?
Except for those with interferon pathway deficiencies, people with PI, also known as inborn errors of immunity (IEI), are not necessarily at higher risk of developing complications from the flu unless they meet other high-risk criteria, such as:
- Being 5 years old or younger (especially younger than 2 years old).
- Being 65 years old or older.
- Have asthma, diabetes, or chronic lung, heart, kidney, liver, metabolic, or blood conditions, including conditions that may be complications of PI.
- Have had a stroke.
- Have a secondary immunodeficiency caused by disease (e.g., HIV or blood cancer) or medication (e.g., immunosuppressive therapy).
- Are pregnant.
The flu's most common complication is bacterial pneumonia, with other complications including viral pneumonia, myocarditis (inflammation of the heart muscle), and worsening of lung diseases. See a healthcare provider right away if you have:
- Difficulty breathing, shortness of breath, or rapid, shallow breathing.
- Blue-ish lips or nail beds.
- Rapid pulse.
- Chest or abdomen pain or pressure.
- Seizures.
- Signs of dehydration (not passing urine).
- A persistent cough, especially if you’re coughing up colored phlegm or mucus (yellow/green).
- Severe muscle pain, weakness, or unsteadiness.
Reye's syndrome is another flu complication that primarily affects children and causes severe vomiting and confusion. To decrease the chance of developing Reye’s syndrome, infants, children, and teenagers should not be given aspirin for fever reduction or pain relief.
What causes the flu and how does it spread?
The flu is caused by influenza viruses. The two main types that infect people, influenza A and influenza B, are genetically different. Influenza A can cause moderate to severe illness in all age groups and infects many species, including pigs, birds, and horses. Influenza B usually causes milder disease and primarily affects children. Both influenza A and influenza B strains cause seasonal outbreaks, typically during the fall and winter months in the U.S. Visit the CDC for this year’s flu season report.
Influenza A strains can also cause flu pandemics, like the 1918 flu and the swine flu in 2009. Pandemics happen when a new influenza A subtype, typically from animals, spreads in human populations that have not ‘seen’ the subtype before and have no immunity to it. Pandemic strains typically go on to become seasonal strains once the human population develops some immunity to them.
Influenza spreads through tiny airborne droplets created by coughing, sneezing, or talking, which can be inhaled or land on mucus membranes in the nose, mouth, or eyes. The flu can also be transmitted orally by kissing or by touching a surface contaminated with the virus and then touching your face. People with PI are equally at risk of contracting the flu as those without PI.
People with the flu are most contagious 1-2 days before symptoms appear and for 4-5 days after. The flu's incubation period is 1-4 days. While most people recover in a few days, some experience severe illness.
How do you avoid the flu?
Get your yearly flu shot
An annual influenza vaccine, or flu shot, is the most effective way to avoid getting seriously ill with the flu. Each year, the Advisory Committee on Immunization Practices (ACIP) at the CDC updates its recommendations for seasonal influenza vaccination. Because the vaccine changes every year to match circulating influenza virus strains, everyone 6 months of age or older needs a flu vaccine every year.
Why should everyone be immunized? First, some people with PI may develop at least some antibodies or a T cell response, which is important for any viral infection, to the vaccine. Immunoglobulin (Ig) replacement therapy products (IVIG or SCIG) typically do not have protective levels of antibodies against current flu strains because manufacturing takes six months or more from the initial plasma donation. Second, household members of people with PI should get vaccinated to create a "protective cocoon" around the person with PI and decrease their exposure to the influenza virus.
For the 2024-2025 season, all flu vaccines are trivalent, which means they protect against three different influenza virus strains, two influenza A strains and one influenza B strain.
There are multiple types of flu vaccines available and selecting the right type is important. The inactivated or recombinant flu vaccine types are best for people with PI and their household members. People with PI and their household members should not receive the live attenuated flu vaccine (trade name FluMist).
Additional recommendations from ACIP include:
- People ages 65 or older should receive the high-dose inactivated (trade name FluZone High-Dose), adjuvanted inactivated (trade name Fluad), or recombinant vaccine (trade name Flubok) because these formulations provide greater protection in older individuals.
- There is some evidence that the adjuvanted inactivated vaccine protects older individuals with risk factors for severe flu better than the high-dose inactivated vaccine, although ACIP does not recommend one over the other.
- Solid organ transplant recipients aged 18-64 who are receiving immunosuppressive medication may receive either high-dose inactivated (FluZone High-Dose) or adjuvanted inactivated (Fluad) influenza vaccines off label, although ACIP does not preferentially recommend them over other options.
- Children 8 years old or younger who have either never been vaccinated for the flu or have only received one previous flu vaccine dose should be vaccinated with two doses of flu vaccine spaced four weeks apart.
- Additional safety measures are no longer recommended for people who are allergic to eggs, regardless of the severity of previous allergic reactions. People with egg allergy may receive any vaccine (egg-based or non-egg-based) that is appropriate for their age and health status.
The flu vaccine is safe and does not cause the flu, and individuals on Ig replacement therapy do not need to coordinate vaccine timing with their treatment. The vaccine is available from late summer, and the CDC recommends getting vaccinated in September or October for the best protection through flu season.
Boost indoor airflow
Respiratory viruses like influenza spread through the air, so crowded, indoor spaces with poor airflow increase the possibility of a sick person infecting others. Simple actions you can take include:
- Opening windows and doors.
- Setting HVAC system fans to run continuously.
- Using high-filtration HVAC filters and replacing them often.
- Using air purifiers/cleaners that meet certain criteria.
Stop the spread
Remember that flu vaccines are a crucial tool during respiratory virus season, but you should take advantage of other tools, too:
- Regularly wash your hands with soap and water for 20 seconds, especially after coughing or sneezing. Hand sanitizer may not be as effective in killing the flu virus.
- Keep physical distance from individuals who are sick.
- Use a well-fitted mask over your nose and mouth to avoid inhaling droplets that can spread respiratory viruses like influenza and COVID-19. During the 2020-2021 and 2021-2022 flu seasons, not many people got the flu because they were wearing masks for COVID-19 prevention, demonstrating that masks are effective against the transmission of both flu and COVID-19.
- Try not to touch your nose, mouth, or eyes, as germs can spread this way.
- During flu season, those with PI should consider avoiding crowded indoor areas such as shopping malls.
- When coughing or sneezing, cover your nose and mouth with a sleeve, elbow, or tissue. Dispose of the tissue after use.
- Stay home from work or school for 3-4 days after experiencing flu symptoms.
What to do if you get the flu
People with PI should discuss plans with their healthcare provider about dealing with the flu before the season begins, including:
- How and where will you get tested for influenza or other, similar respiratory viruses like COVID-19?
- What antiviral medication does your healthcare provider recommend and how will you get it?
- What symptoms should you pay particular attention to?
In case of illness, those with PI should immediately contact their healthcare provider to get tested for influenza and start antiviral treatment, which is most effective within 48 hours of symptoms appearing.
There are several FDA-authorized or approved at-home antigen tests designed to detect influenza A and B, as well as SARS-CoV-2 (the virus that causes COVID-19). Note that antigen tests vary in accuracy and can give 'false negative' results, which means the test may not detect the virus even if you do have the flu or COVID-19. If you take an at-home test and it is negative, follow the manufacturer's instructions for retesting and consider getting a more sensitive PCR test (sometimes called a NAAT or molecular test). These tests are typically available at pharmacies, urgent care centers, and healthcare provider offices.
COVID-19 and PI
Learn more about COVID-19, how to protect yourself, and what to do if you get sick.
Latest infectious disease resources
This page contains general medical and/or legal information that cannot be applied safely to any individual case. Medical and/or legal knowledge and practice can change rapidly. Therefore, this page should not be used as a substitute for professional medical and/or legal advice. Additionally, links to other resources and websites are shared for informational purposes only and should not be considered an endorsement by the Immune Deficiency Foundation.
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