What is the flu? 

Influenza (or commonly known as the flu) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. Some people, such as older people, young children, and people with certain health conditions, are at higher risk of serious flu complications.  There are two main types of influenza viruses: Types A and B. The influenza A and B viruses that routinely spread in people are responsible for seasonal flu epidemics each year. 

What are the signs and symptoms of the flu? 

Flu symptoms usually come on suddenly. People who have flu often feel some or all of these symptoms: 

  • Fever or feeling feverish/chills 
  • Cough 
  • Sore throat 
  • Runny or stuffy nose 
  • Muscle or body aches 
  • Headaches 
  • Fatigue (tiredness) 
  • Some people may have vomiting and diarrhea, though this is more common in children than adults. 

How is the flu spread? 

People with the flu are most contagious in the first three to four days after their illness begins.  Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children and some people with weakened immune systems may pass the virus for longer than 7 days. 

Symptoms can begin from 1 to 4 days after the virus enters the body. That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Some people can be infected with a flu virus but have no symptoms. During this time, those people may still spread the virus to others. 

Is there more than one type of flu shot available? 

Yes. There are different flu vaccine manufacturers and multiple flu vaccines that are licensed and recommended for use in the United States. 

New for this season: For people 65 years and older, there are three flu vaccines that are preferentially recommended over standard-dose. These are Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant flu vaccine and Fluad Quadrivalent adjuvanted flu vaccine. 

All flu vaccines for the 2022-2023 season are quadrivalent vaccines, designed to protect against four different flu viruses, including two influenza A viruses and two influenza B viruses. 

Why do some people not feel well after getting a flu shot? 

Flu vaccine side effects are generally mild and go away on their own within a few days. Some side effects that may occur from a flu shot include soreness, redness, and/or swelling where the shot was given, headache, fever, nausea, muscle aches, and fatigue. The flu shot, like other injections, can occasionally cause fainting. 

Healthy habits to help protect against the flu:

  • Avoid close contact. 
  • Stay home when you are sick. 
  • Cover your mouth and nose. 
  • Clean your hands. 
  • Avoid touching your eyes, nose, or mouth. 
  • Practice other good health habits. 

What should I do if I get sick? 

Take antiviral drugs, if prescribed by a health care provider 

Take everyday precautions to protect others while sick 

  • While sick, limit contact with others as much as possible to keep from infecting them. 
  • Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it. 
  • Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub. 
  • Clean and disinfect surfaces and objects that may be contaminated with germs like flu. 
  • Stay home until you are better 

 What antiviral drugs are recommended this flu season? 

  • Oseltamivir phosphate (trade name Tamiflu®) is available as a pill or liquid suspension and is FDA approved for early treatment of flu in people 14 days and older. Patient should take Oseltamivir within 48 hours of flu symptom onset. Duration is 5 days. It’s best to take Tamiflu with food; there is less chance of stomach upset if you take it with a light snack or a meal. The most common side effects reported by people using oseltamivir phosphate in clinical trials included nausea and vomiting.  
  • Baloxavir marboxil (trade name Xofluza®) is a pill given as a single dose by mouth and is approved for early treatment of flu in children aged 5 years to less than 12 years who do not have any chronic medical conditions, and for all people aged 12 years and older. CDC does not recommend use of baloxavir in pregnant people, breastfeeding people, and outpatients with complicated or progressive illness, severely immunosuppressed people, or hospitalized patients because of the lack of information on use of baloxavir for these groups to date. The most common side effects reported by people using baloxavir in clinical trials included diarrhea, bronchitis, nausea, sinusitis, and headache. 


Written by:

Thanh Lo 

PharmD Candidate, 2023 

Temple University of Pharmacy 



Influenza (flu). Centers for Disease Control and Prevention. https://www.cdc.gov/flu/index.htm. Published August 26, 2022. Accessed September 19, 2022.  

Tamiflu® (oseltamivir phosphate): Dosing for flu (influenza) treatment. tamiflu. https://www.tamiflu.com/taking-tamiflu.html. Accessed September 19, 2022.