Flu

The flu (influen­za) is a con­ta­gious ill­ness that tends to come on sud­den­ly with fever, body aches, fatigue, and cough. It affects all ages and is usu­al­ly worse than a cold. Most peo­ple recov­er in a week with rest and flu­ids, but the flu can be seri­ous, so antivi­ral med­i­cine and an annu­al flu shot help, espe­cial­ly for high­er-risk groups.

Find a pri­ma­ry care provider or pediatrician

Find an Imme­di­ate Care Cen­ter near you

What is the flu?

The flu, short for influen­za, is a con­ta­gious res­pi­ra­to­ry ill­ness caused by influen­za virus­es. It spreads eas­i­ly from per­son to per­son and tends to cir­cu­late in fall and win­ter. Unlike a com­mon cold, which comes on slow­ly and stays mild, the flu usu­al­ly hits sud­den­ly and can knock you flat with fever, aches, and exhaustion.

One of the most com­mon ques­tions is whether it is the flu or just a cold. Here is how they usu­al­ly compare:

Clue	Flu	Cold
How it starts	Sud­den­ly, over a few hours	Grad­u­al­ly, over a day or two
Fever	Com­mon, often higher	Rare, usu­al­ly mild
Body aches	Com­mon, often severe	Mild if any
Fatigue	Com­mon, can be extreme	Mild
Cough, sore throat	Com­mon	Com­mon
Run­ny nose, sneezing	Some­times	Com­mon

Scroll to view more

COVID-19 can look a lot like the flu, so when it mat­ters, a quick test can tell them apart.

What are the symp­toms of the flu?

Flu symp­toms often come on fast and can include:

• Fever or feel­ing fever­ish, and chills (though not every­one with flu has a fever)
• Cough and sore throat
• Run­ny or stuffy nose
• Mus­cle or body aches
• Headache
• Fatigue, which can be extreme
• In chil­dren espe­cial­ly, vom­it­ing and diarrhea

Adults and old­er kids often describe a sud­den hit-by-a-truck feel­ing. In babies and young chil­dren, the flu may show up as fever, fussi­ness, poor feed­ing, and being unusu­al­ly sleepy or hard to com­fort. Most peo­ple start feel­ing bet­ter with­in about a week, though a cough and tired­ness can linger.

When should I get care?

Most healthy peo­ple recov­er from the flu at home, but some should reach out ear­ly, and cer­tain symp­toms are emer­gen­cies. Act­ing ear­ly mat­ters, because antivi­ral med­i­cine works best when start­ed with­in about two days of get­ting sick.

Call your provider or pedi­a­tri­cian ear­ly, espe­cial­ly if high­er risk

Reach out soon, ide­al­ly in the first day or two, if you or your child is at high­er risk for flu com­pli­ca­tions or if symp­toms are severe. High­er-risk groups include young chil­dren (espe­cial­ly under 5), adults 65 and old­er, preg­nant peo­ple, and any­one with a con­di­tion like asth­ma, dia­betes, or heart or lung dis­ease. A provider can decide whether antivi­ral med­i­cine makes sense. Video and imme­di­ate care vis­its make this easy.

Find a pri­ma­ry care provider or pediatrician

Start a video vis­it or vis­it imme­di­ate care

Get emer­gency care

Some flu symp­toms are emer­gen­cies. Call 911 or go to the near­est ER for any of these:

What caus­es the flu and how does it spread?

The flu is caused by influen­za virus­es, main­ly types A and B, which change a bit every year (which is why the vac­cine is updat­ed annu­al­ly). It spreads through droplets when an infect­ed per­son coughs, sneezes, or talks, and by touch­ing a con­t­a­m­i­nat­ed sur­face and then your face. Peo­ple are usu­al­ly con­ta­gious from about a day before symp­toms start through five to sev­en days after, and chil­dren can spread it longer. That is why stay­ing home while sick, and until fever-free for 24 hours with­out fever med­i­cine, helps pro­tect others.

How is the flu treated?

For most peo­ple, the flu is treat­ed with rest and good home care while the body fights it off. Antibi­otics do not work on the flu because it is caused by a virus, not bacteria.

Home care

• Rest and plen­ty of fluids
• Aceta­minophen or ibupro­fen for fever and aches (nev­er give aspirin to chil­dren or teens)
• For chil­dren, dose fever med­i­cine by weight and fol­low the age guid­ance, and ask your pedi­a­tri­cian about babies
• Stay­ing home to recov­er and avoid spread­ing it

Antivi­ral medicine

Pre­scrip­tion antivi­ral med­i­cines (such as oseltamivir) can short­en the flu and low­er the risk of com­pli­ca­tions, but they work best when start­ed with­in about 48 hours of symp­toms. They are espe­cial­ly rec­om­mend­ed for peo­ple at high­er risk and for severe ill­ness, and they can be used in children.

Can the flu be prevented?

The best pro­tec­tion is an annu­al flu vac­cine, rec­om­mend­ed for near­ly every­one 6 months and old­er, includ­ing chil­dren and preg­nant peo­ple. It is updat­ed each year to match cir­cu­lat­ing strains, and while no vac­cine is per­fect, it makes the flu less like­ly and usu­al­ly milder if you do catch it. Every­day habits help too:

• Get the flu shot each fall
• Wash hands often and cov­er coughs and sneezes
• Avoid close con­tact with peo­ple who are sick
• Stay home when you are sick to pro­tect others

Vac­ci­nat­ing every­one in the house­hold, includ­ing kids, also helps pro­tect babies too young for the shot and fam­i­ly mem­bers at high­er risk.

Who treats the flu?

The flu is usu­al­ly man­aged at home or by a pri­ma­ry care provider or pedi­a­tri­cian. Pedi­atric, inter­nal med­i­cine, and fam­i­ly med­i­cine providers, with the nurse prac­ti­tion­ers and physi­cian assis­tants on their teams, can con­firm the flu, decide whether antivi­ral med­i­cine is right, treat symp­toms, and advise on when to wor­ry. Imme­di­ate care vis­its are con­ve­nient when you need to be seen quickly.

Some sit­u­a­tions call for more:

• Pedi­atrics, for infants, chil­dren, and teens
• Inter­nal med­i­cine and fam­i­ly med­i­cine, for adults and whole-fam­i­ly care
• Pul­monolo­gy, when the flu leads to a breath­ing com­pli­ca­tion like pneu­mo­nia, or for peo­ple with chron­ic lung conditions
• The ER, for emer­gency warn­ing signs at any age

Your provider coor­di­nates care and brings in a spe­cial­ist or refers to the hos­pi­tal when the flu becomes severe.

Fre­quent­ly asked questions

Is it the flu or a cold?

The biggest clues are speed and sever­i­ty. The flu usu­al­ly comes on sud­den­ly with fever, body aches, and exhaus­tion, while a cold builds slow­ly and stays milder, most­ly a run­ny nose and sneez­ing. Colds rarely cause a high fever or knock you off your feet the way the flu does. COVID-19 can look sim­i­lar to the flu, so a test is the sure way to tell when it matters.

How long is the flu contagious?

Peo­ple with the flu are usu­al­ly con­ta­gious from about a day before symp­toms start until five to sev­en days after, and chil­dren and peo­ple with weak­ened immune sys­tems can spread it longer. A good rule is to stay home until you have been fever-free for 24 hours with­out using fever-reduc­ing medicine.

When should I wor­ry about my child’s flu?

Get emer­gency care if your child is breath­ing fast or hard, has bluish lips, is not drink­ing or has no wet dia­pers or tears, is too sleepy to wake or inter­act, or has a fever that will not come down or that improves then returns worse. Any fever in a baby under 2 months needs care right away. When in doubt, call your pediatrician.

Does the flu shot give you the flu?

No. The flu shot can­not give you the flu; it con­tains an inac­ti­vat­ed virus or no live virus at all. Some peo­ple feel a lit­tle achy or run a low fever for a day as the immune sys­tem responds, which is not the flu. The vac­cine is the best way to low­er your risk and is rec­om­mend­ed for near­ly every­one 6 months and older.

Where can I get care or a flu shot in Chicagoland?

Duly Health and Care offers pedi­atric and adult pri­ma­ry care, fam­i­ly med­i­cine, video vis­its, and imme­di­ate care across the Chica­go sub­urbs, so you can get checked for the flu, ask about antivi­ral med­i­cine, or get your annu­al flu shot, for the whole fam­i­ly. For emer­gency warn­ing signs, seek care right away.

Care at Duly Health and Care

The flu is com­mon and usu­al­ly pass­es with rest, but it can hit hard, and know­ing when it is more than a bad week makes all the dif­fer­ence. Duly pedi­atric and pri­ma­ry care providers can con­firm the flu, decide whether antivi­ral med­i­cine would help (it works best start­ed ear­ly), treat symp­toms, and tell you what to watch for, often through a quick video or imme­di­ate care vis­it. They can also keep your fam­i­ly pro­tect­ed with the annu­al flu shot.

With pedi­atric and adult pri­ma­ry care, fam­i­ly med­i­cine, and pul­monolo­gy exper­tise across the Chica­go sub­urbs, plus video and imme­di­ate care, help is easy to reach when the flu hits.

Find a provider or pediatrician

Sched­ule a video vis­it or vis­it imme­di­ate care

Med­ical­ly reviewed by Brett Hurli­man, MD · Last reviewed June 2026