Influenza and Colds: Symptoms, Strains, and Treatment
Author: Disabled World (DW)
Updated/Revised Date: 2 Nov 2026
Table of Contents:
Synopsis - Definition - About This Section - FAQs - Publications - Subtopics
Synopsis
Learn how influenza and colds differ, their common symptoms and virus strains, plus vaccination and treatment options to help prevent and relieve illness.
At a Glance
- 1 - Only influenza A viruses are known to have caused pandemics.
- 2 - Influenza D viruses mainly affect cattle and are not known to infect people.
- 3 - Since 2010, flu has led to between 120,000 and 710,000 hospitalizations a year in the United States.
- 4 - CDC recommends four FDA-approved antiviral drugs to treat the flu, including oseltamivir and baloxavir.
Topic Definition
- Influenza
Influenza is a contagious respiratory infection caused by RNA viruses of the family Orthomyxoviridae, mainly affecting the nose, throat, bronchi, and sometimes the lungs. It usually comes on suddenly with high fever, chills, muscle aches, headache, sore throat, and a dry cough, and most people recover within about a week. The viruses spread through the air by coughs and sneezes, as well as through contact with contaminated surfaces or body fluids. While many cases are mild, influenza can become serious or even fatal for older adults, newborns, and people with chronic health conditions, which is why annual vaccination remains one of the most reliable ways to reduce the risk.
Overview
What is Influenza?
Influenza, or the flu, is a contagious respiratory infection caused by influenza viruses, which are RNA viruses of the family Orthomyxoviridae. It occurs in all parts of the world. There are around a billion cases of seasonal influenza each year worldwide, including 3 to 5 million cases of severe illness, and the flu causes 290,000 to 650,000 respiratory deaths a year [World Health Organization, 2025].
The flu usually starts suddenly with fever, a dry cough, headache, muscle and joint pain, a strong feeling of being unwell, sore throat, and runny nose. Most people recover within about a week without medical care, but the flu can cause severe illness or death, especially in young children, older adults, pregnant women, and people with chronic medical conditions or weakened immune systems.
The Common Cold
A cold is a viral infection of the upper respiratory tract. More than 200 viruses can cause colds, and rhinoviruses are the most frequent cause in the United States. Adults have an average of two to three colds a year, and children often have more. Colds usually last less than a week and can cause a runny or stuffy nose, sneezing, sore throat, cough, headache, mild body aches, and sometimes a low fever [Centers for Disease Control and Prevention, 2026].
There is no cure for a cold. Rest, fluids, and over-the-counter medicines can ease the symptoms, but antibiotics do not work against cold viruses. Washing hands often, not touching the eyes, nose, and mouth with unwashed hands, and keeping away from people who are sick help prevent colds.
Read about the differences between colds and influenza including related symptoms.
Types of Influenza Viruses
There are four types of influenza viruses: A, B, C, and D. Influenza A and B viruses circulate in people and cause seasonal epidemics. Influenza A viruses are divided into subtypes by the proteins on their surface, and the subtypes now circulating in people are A(H1N1) and A(H3N2). Only type A viruses are known to have caused pandemics. Influenza C is found less often and usually causes mild infections, and influenza D mainly affects cattle and is not known to infect people [World Health Organization, 2025].
Seasonal flu is different from flu viruses that mainly infect animals, such as avian flu and canine flu. In 2009 a new A(H1N1) virus, widely known as swine flu, caused a pandemic and then replaced the A(H1N1) virus that had circulated before.
How the Flu Spreads
The flu spreads easily, especially in crowded places such as schools and nursing homes. When an infected person coughs or sneezes, droplets containing the virus are released into the air and can infect people nearby, and the virus can also spread on hands. Symptoms begin about 2 days after infection, with a range of 1 to 4 days. In temperate climates, flu epidemics occur mainly in winter, while in tropical regions the flu can occur all year.
Flu Symptoms and Complications
Common symptoms of the flu include:
- Sudden fever
- Cough, usually dry, which can be severe and last 2 weeks or more
- Headache
- Muscle and joint pain
- Severe malaise (feeling very unwell)
- Sore throat
- Runny nose
Some people, more often children, also have vomiting and diarrhea. The flu can lead to pneumonia and sepsis and can make chronic conditions such as asthma, lung disease, and heart failure worse. In industrialized countries, most deaths linked to the flu occur among people aged 65 or older.
The Flu in the United States
CDC estimates that since 2010, except for the 2020 to 2021 season, flu has caused between 9.4 million and 51 million illnesses and between 120,000 and 710,000 hospitalizations in the United States each year [Centers for Disease Control and Prevention, n.d.-b].
Flu Vaccination
Vaccination is the best way to prevent the flu. Flu vaccines have been used safely for more than 60 years, and because immunity fades over time and the viruses keep changing, a new vaccine is needed every year. CDC recommends a yearly flu vaccine for everyone 6 months of age and older, with rare exceptions. The World Health Organization especially recommends yearly vaccination for:
- Pregnant women
- Children aged 6 months to 5 years
- People over age 65
- People with chronic medical conditions
- Health workers
Vaccines are updated regularly to match the viruses expected to circulate. Inactivated and recombinant flu vaccines are given as shots, and a live attenuated vaccine is given as a nasal spray. The vaccine may work less well in older people, but it still makes the illness milder and lowers the chance of complications and death.
Treating the Flu
Most people with the flu recover on their own with rest, plenty of fluids, and medicine for fever, and people with mild illness should stay home to avoid infecting others. People at high risk or with severe symptoms should be treated with antiviral medicine as soon as possible. CDC recommends four FDA-approved antiviral drugs: oseltamivir (Tamiflu), zanamivir (Relenza), peramivir (Rapivab), and baloxavir marboxil (Xofluza). Started soon after symptoms begin, they can shorten the illness by about a day and help reduce some complications [Centers for Disease Control and Prevention, n.d.-c].
Flu Facts and Statistics
- Ninety-nine percent of deaths in children under 5 with flu-related lower respiratory tract infections occur in developing countries.
- Percent of children 6 months to 17 years vaccinated against flu in the 2024 to 2025 season: 50.2%
- Percent of adults 18 years and over vaccinated against flu in the 2024 to 2025 season: 41.9%
Sources: World Health Organization; CDC FluVaxView, 2024 to 2025 influenza season.
Frequently Asked Questions
Can you have the flu without a fever?
Yes, some people, especially older adults, can have influenza without a noticeable fever while still experiencing cough, fatigue, and body aches.
How long is a person with the flu contagious?
Most adults can spread influenza from about one day before symptoms begin until roughly five to seven days after becoming sick.
Is it safe to exercise while I have the flu?
Rest is generally recommended during influenza, and strenuous exercise should be avoided until the fever and body aches have fully resolved.
Can I get the flu shot if I have a mild cold?
A mild cold without a fever is usually not a reason to delay the flu shot, but you should check with your health provider if you feel unwell.
Why do I still get the flu even after vaccination?
The vaccine reduces risk and severity, but circulating strains can differ from those in the vaccine, so some vaccinated people still get infected.
Does cold weather itself cause the flu?
Cold weather does not directly cause the flu, but people gather indoors more often in winter, which helps the virus spread between individuals.
When should I see a doctor about flu symptoms?
You should seek care if you have trouble breathing, chest pain, a persistent high fever, or symptoms that improve and then suddenly return worse.
What is the difference between a cold and the flu?
Colds usually come on slowly with a runny nose and sore throat, while flu tends to start suddenly with fever, body aches, and exhaustion. Flu is more likely to cause serious complications such as pneumonia.
References
- Centers for Disease Control and Prevention. (2026). About common cold.
- Centers for Disease Control and Prevention. (n.d.-b). Facts about estimated flu burden.
- Centers for Disease Control and Prevention. (n.d.-c). Treating flu with antiviral drugs.
- World Health Organization. (2025). Influenza (seasonal) [Fact sheet].
Curated and edited by Ian C. Langtree, Founder and Editor-in-Chief, Disabled World. This section is maintained by the Disabled World editorial team. Last updated: