High-risk groups: who needs to be most careful
For most healthy adults, flu is a miserable week that resolves on its own. For certain groups, it can escalate quickly into pneumonia, hospitalization, or worse. Knowing which category you're in changes what you should do — and how fast you need to do it.
Why risk varies so much
Flu complications aren't random. They follow predictable patterns driven by age-related immune function, underlying conditions that impair the respiratory or immune system, and physiological states like pregnancy that alter how the body responds to infection. The CDC estimates that over 90% of flu-related deaths occur in people 65 and older, and the vast majority of hospitalizations occur in people with at least one underlying condition.
The key actions for high-risk individuals are the same as for everyone — vaccinate, test early, act on positive results quickly — but the urgency is higher and the threshold for calling a doctor is lower. What a healthy 35-year-old can reasonably manage at home may require medical attention in a 72-year-old with COPD.
Age-related immune decline (immunosenescence) means older adults mount a slower, weaker initial response to flu infection. The virus has more time to replicate before the immune system catches up, leading to more severe illness and higher rates of complications including pneumonia, cardiac events, and exacerbations of underlying conditions.
Vaccination: Get vaccinated as early as possible each fall. Ask specifically for a high-dose or adjuvanted formulation — Fluzone High-Dose Quadrivalent or Fluad Quadrivalent. These are specifically designed for adults 65+ and produce a stronger immune response than standard-dose vaccines. They're covered by Medicare Part B at no cost. Standard-dose vaccines are better than nothing, but high-dose is meaningfully superior for this age group.
If you get flu: Contact your doctor on the first day of symptoms, not when things get worse. Antivirals are generally recommended for all adults 65+ with flu regardless of symptom severity. Don't wait 48 hours — get the prescription the same day you have symptoms.
Young children haven't yet built the immune experience to respond quickly to flu. Their airways are also narrower, making respiratory complications more serious relative to adults. Children under 2 are at highest risk; flu is among the leading causes of pediatric hospitalization each year, and most children who die from flu were otherwise healthy.
Vaccination: Flu vaccine is recommended starting at 6 months. Children receiving their first-ever flu vaccine need two doses spaced four weeks apart — a detail often missed. For healthy children ages 2–17, FluMist nasal spray is an option if they strongly resist shots.
If your child gets flu: Call your pediatrician the same day symptoms appear. Children under 5 (especially under 2) are generally candidates for antiviral treatment. Monitor closely for warning signs: breathing faster than normal, blue-tinged skin or lips, not waking normally, extreme irritability, or inability to drink fluids. These warrant emergency care.
Pregnancy alters immune function, cardiac output, and lung capacity in ways that make flu both more likely to become severe and harder for the body to recover from. Pregnant women with flu have higher rates of hospitalization, premature delivery, and serious respiratory complications than non-pregnant women of the same age.
Vaccination: The flu vaccine is safe at any stage of pregnancy and is strongly recommended. Maternal antibodies cross the placenta, providing the newborn with passive immunity for the first months of life — before infants are old enough to receive their own vaccine. Getting vaccinated in pregnancy is one of the most effective ways to protect a newborn during their most vulnerable window.
If you get flu while pregnant: Contact your OB or midwife the same day. Antivirals are generally recommended for pregnant women with flu — the benefit clearly outweighs the risk at any stage of pregnancy. Fever in pregnancy (especially in the first trimester) carries its own risks to the developing fetus, making fever control with acetaminophen important.
Flu is one of the most common triggers for asthma attacks and COPD exacerbations. Airway inflammation from the viral infection directly worsens underlying respiratory conditions, and the complication can quickly become an emergency requiring hospitalization or mechanical ventilation.
Vaccination: Annual flu vaccination is especially important for people with asthma or COPD. The inactivated flu shot (injection) is recommended — the live attenuated nasal spray (FluMist) is not recommended for people with asthma.
If you get flu: Contact your doctor immediately. Have your rescue inhaler accessible and follow any action plan your pulmonologist or allergist has given you. Any increase in breathing difficulty or change in sputum color warrants prompt evaluation.
Multiple studies have found that flu infection increases the risk of heart attack in the days immediately following illness — by as much as six times in the week after flu diagnosis compared to baseline. The mechanism involves inflammation, increased clotting tendency, and the cardiovascular stress of fever and systemic infection. Flu vaccination has been associated with reduced risk of major cardiac events in people with existing heart disease.
Vaccination: Strongly recommended. Flu vaccination in people with existing cardiovascular disease reduces hospitalization and cardiac event risk. Get vaccinated annually, ideally in September or October.
If you get flu: Low threshold for contacting your cardiologist or primary care doctor. Any chest pain, palpitations, or unusual shortness of breath during or after flu warrants prompt evaluation — don't assume it's "just the flu."
Diabetes impairs immune function and makes it harder to fight off infection. Flu-related illness can destabilize blood sugar control significantly, sometimes requiring hospitalization for glycemic management independent of the infection's severity. Kidney and liver disease impair the body's ability to clear the virus and process medications. Obesity (BMI ≥40) is independently associated with higher flu severity and hospitalization risk.
Vaccination: All of these groups are CDC priority populations for annual flu vaccination. Get vaccinated as early in the season as possible.
If you get flu: Monitor blood glucose more frequently if diabetic. Contact your doctor early — antivirals are generally recommended for all of these groups. Watch for dehydration, which can worsen kidney function and blood sugar control simultaneously.
People receiving chemotherapy, those who have had organ transplants, people living with HIV (especially with low CD4 counts), and others with significantly impaired immune systems face heightened flu risk in multiple ways. Illness tends to be more severe and last longer. Viral shedding — the period of contagiousness — is extended, sometimes for weeks. And symptoms may not follow the typical pattern, making diagnosis harder.
Vaccination: The inactivated flu shot is safe for immunocompromised individuals and is recommended annually. FluMist (live attenuated) is not recommended. Note that vaccine effectiveness may be reduced in people with severely compromised immune systems — vaccination is still recommended, but additional precautions (masking in crowded settings, avoiding known flu contacts) are important alongside it.
If you get flu: Contact your oncologist, transplant team, or infectious disease specialist immediately. Antiviral treatment is strongly recommended and should be started as early as possible. Extended or higher-dose antiviral regimens are sometimes used. Monitor closely for complications — fever, unusual fatigue, or respiratory symptoms that don't follow an expected course all warrant prompt evaluation.
Testing: do it at first symptom, not when things get worse. Calling your doctor: same day, not after 48 hours. Going to urgent care or the ER: any difficulty breathing, chest pain, confusion, or symptoms not following a normal trajectory. The 48-hour antiviral window matters for everyone, but it matters most for people whose illness is most likely to escalate.