Overview
Get answers to commonly asked questions about influenza viruses and vaccination from UCSF's Occupational Health Services (OHS).
About the flu
Flu season occurs annually from fall to spring, marked by the widespread transmission of influenza viruses. Receiving a flu shot is the most effective way to protect against the flu, significantly reducing the risk of infection and its complications. The vaccine is updated yearly to match circulating strains and is recommended for everyone over six months old, particularly vulnerable groups like the elderly, young children, and those with chronic health conditions. Besides individual protection, widespread vaccination helps achieve community immunity, reducing the overall prevalence of the flu and easing the burden on healthcare systems.
For more detailed information, visit the Centers for Disease Control (CDC) Flu Information page.
Q&A
The flu, or influenza, is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and, at times, can lead to death.
Yes, the flu can lead to serious complications, especially for young children, elderly people, pregnant women, and people with certain chronic health conditions.
The flu is caused by influenza viruses that infect the nose, throat, and sometimes the lungs. The virus spreads mainly by droplets when people with the virus cough, sneeze, or talk. It’s also possible to be infected by touching surfaces or objects with flu virus and then touching your mouth, nose, or eyes.
Fever or feeling feverish/chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue (tiredness), vomiting and diarrhea (more common in children).
The flu often comes on suddenly with high fever, body aches, fatigue, and more severe respiratory symptoms, while a cold typically develops gradually with milder symptoms.
If you think you have the flu, stay home to avoid spreading the virus. Rest, stay hydrated, and use over-the-counter medications to manage symptoms. If you are in a high-risk group, have severe symptoms or have any concerns, contact your healthcare provider.
If you have severe symptoms such as difficulty breathing, chest pain, sudden dizziness, or if you are in a high-risk group or have any concerns, you should seek medical attention.
Annual flu vaccination, good health habits such as avoiding close contact with sick people, covering coughs and sneezes, and washing hands often, and antiviral drugs if prescribed by a doctor.
While the effectiveness of the flu vaccine can vary from year to year, it still significantly reduces your risk of getting the flu. If you do get sick, having the flu shot can make your illness milder and reduce the risk of serious complications and hospitalization.
Yes, it is recommended to get the flu shot every year because the flu virus changes constantly. Each year, the vaccine is updated to protect against the most current strains. Annual vaccination ensures the best possible protection and helps protect those around you, especially high-risk populations such as infants, the elderly, and those with weakened immune systems. Getting vaccinated decreases, the likelihood of spreading the flu to others.
No, the flu vaccine cannot cause the flu. Some people may experience mild side effects like a sore arm or low-grade fever, but these are not the flu.
Serious side effects from the flu shot are extremely rare. Severe allergic reactions can occur but are very uncommon. If you have a history of severe allergies, discuss this with your healthcare provider before getting the flu shot. Most people experience only mild side effects, such as arm soreness at the injection site, mild fever, or muscle aches. These mild side effects usually go away within a few days.
Getting the flu can be dangerous and lead to severe complications, including hospitalization and death. The flu shot is recommended because it provides immunity without the risk of serious illness.
Yes, it is still recommended to get the flu shot. Even if you’ve never had the flu, new strains of the virus emerge putting you at risk. Vaccination helps protect you and others in your community.
Some people believe the flu shot is bad due to misconceptions and fears, such as:
- Belief that the flu shot can give you the flu (it cannot, as it contains inactivated virus or a protein from the virus)
- Concerns about vaccine safety and side effects
- Mistrust of pharmaceutical companies or healthcare systems
- Belief that natural immunity is better than vaccination
If you have concerns about getting the flu shot, talk to your healthcare provider. They can provide you with information, address your concerns, and help you make an informed decision based on your health needs and risks.
Yes, there are alternatives. Ask your healthcare provider about the nasal spray flu vaccine, which is needle-free and approved for use in healthy people between the ages of 2 and 49.
You can get a flu vaccine at local pharmacies like CVS and Walgreens, healthcare providers, and community clinics. There is often free flu vaccination clinics organized by the The San Francisco Dept. Of Public Health (SFDPH) and community organizations. Check local health department announcements and websites for the latest information.
Monitor updates from the SFDPH website and the California Department of Public Health. You can also sign up for health alerts from these organizations. Reliable information can also be found on the CDC website, and local healthcare providers' websites.