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Flu (Seasonal Influenza)

Learn about the flu (seasonal influenza) and how to protect yourself and your family this flu season.

The Flu (seasonal influenza) is a contagious illness caused by the influenza virus. Flu symptoms can range from mild to severe and include fever, cough, muscle aches, headache, runny nose, sore throat, and general weakness. The onset of these symptoms may be sudden. Most flu activity occurs from from October through March each year. The easiest way to protect you and your family from flu is by getting the flu vaccine.

The basics

How does the flu spread?

The viruses that cause flu live in the nose and throat. They spray into the air when an infected person sneezes, coughs, or talks. People nearby then breathe in the virus. Flu symptoms usually start 1 to 4 days after a person breathes in the virus, but it can take longer. Most people can spread the flu virus 1 day before their symptoms begin until about a week afterward.​

Who is at higher risk for severe illness?

Young children and people 65 years and older are at high risk for developing severe illness from the flu. Individuals with health conditions are also at higher risk for serious illness from the flu. These medical conditions include asthma, diabetes, and heart disease. 

How long does the flu season last?

Most influenza activity in Boston occurs from October to March each year.

How serious is the flu?

Influenza is unpredictable and can be severe. Between 1976 and 2006, CDC estimates from 3,000 to 49,000 people died each year from influenza.


How can I prevent the flu?

There are many ways you can help prevent the spread of germs.

  • Getting vaccinated is the best protection against influenza. To find a local vaccination site, contact your health care provider. Most options are completely covered by health insurance. For this winter season (2023-2024), the Boston Public Health Commission is hosting free, walk-in flu vaccination clinics for people of all ages at the Bruce C. Bolling Municipal Building clinic in Nubian Square and City Hall. Walk-ins are welcome, no appointments or proof of insurance are needed. Clinic hours are posted online.
  • Cover your mouth and nose with a tissue when you cough or sneeze. If you don't have a tissue, cough or sneeze into your upper sleeve.
  • Wash your hands often with soap and water or use an alcohol-based hand gel.
  • Keep your hands away from your eyes, nose, and mouth.
  • Clean surfaces in your home regularly with a household cleaner.
  • Avoid close contact with people who are sick when possible.
  • If you become sick, stay home. A person with the flu should stay home for 24 hours after their fever has gone away without using medicine. For most people, this will be at least 4 days.
Who should get a flu vaccine?

Everyone 6 months and older should get vaccinated for the flu. Vaccinating is the best way to protect yourself and those around you. Certain people are at greater risk for serious illness if they get influenza. High risk people include the elderly, young children, and pregnant women. Health conditions such as asthma, diabetes, and heart disease also put people at higher risk for serious illness from the flu. Individuals that are not high risk can still pass the virus to others who are high risk. The flu vaccine provides individual and community protection against the flu.


The flu vaccine is available from primary care providers and at many pharmacies. Most health insurance plans cover the cost of a flu vaccine.

Free, walk in flu vaccine clinics 

Bruce C. Bolling Municipal Building

2302 Washington St, Roxbury, MA 02119

  • Thursdays through Saturdays: 12p.m. - 6 p.m.

Boston City Hall

1 City Hall Square, Boston, MA 02201; Room 115

  • Mondays: 7 a.m. - 1 p.m.
  • Wednesdays: 12 p.m. - 5 p.m.
Questions about the flu Vaccine?

It's normal to have questions about vaccines. Read our Frequently Asked Questions and find out more about some common flu vaccine myths.


If you do not have health insurance, or if co-pays are a barrier, call the Mayor’s Health Line at 617-534-5050 or toll free at 800-847-0710

Flu Data

Flu Data
Week Number of Reported Influenza Cases among Boston Residents
10/01/2022 - 10/07/2022   19
10/08/2022 - 10/14/2022   21
10/15/2022 - 10/21/2022   28
10/22/2022 - 10/28/2022   52
10/29/2022 - 11/04/2022   106
11/05/2022 - 11/11/2022   129
11/12/2022 - 11/18/2022  239
11/19/2022 - 11/25/2022  361
11/26/2022 - 12/02/2022


12/03-2022 - 12/09/2022 944
12/10/2022 - 12/16/2022 916
12/17/2022 - 12/23/2022 753
12/24/2022 - 12/30/2022 448
12/31/2022 - 01/06/2023 260
01/07/2023 - 1/13/2023 117
1/14/2023 - 1/20/2023 81
1/21/2023 - 1/27/2023 58
1/28/2023 - 2/03/2023 26
2/04/2023 - 2/10/2023 27
2/11/2023 - 2/17/2023 22
2/18/2023 - 2/24/2023 19
2/25/2023 - 3/3/2023 17
3/4/2023 - 3/10/2023 19
3/11/2023 - 3/17/2023 7
3/18/2023 - 3/24/2023 12
3/25/2023 - 3/31/2023 23
4/01/2023 - 4/07/2023 15

Case numbers are updated as of April 11, 2023

Reported Influenza Cases Among Boston Residents, 2021 and 2022. Data Displayed in chart above.


Info for businesses and employers

During flu season, businesses and employers play a key role. Businesses have to protect employee health and safety and without any negative economic impact. Take steps to limit the spread of influenza, and keep your employees and community healthy.

Develop a Business Continuity Plan

Identify your office’s essential functions and the individuals who perform them. Train enough people to  perform essential functions and allow for potential absenteeism.

Review and Update Sick Leave Policies
  • Employees with the flu should stay home until they have been fever free without fever reducing medicines for 24 hours. For most this will be at least 4 days
  • Employees with sick minors should stay home with them if necessary
Reduce the Spread of Infection

Encourage good infection control practices in the workplace. Display posters about proper hand washing, respiratory hygiene, and cough etiquette. Everyone should cover their nose and mouth with a tissue when they cough or sneeze. Throw the tissue in the trash after using it.  

  • Encourage hand washing. Provide enough facilities for hand washing
  • Put alcohol-based hand sanitizer in common areas such as lobbies, corridors, and restrooms. Hand sanitizers should have at least a 60% alcohol base
  • Provide tissues, disinfectants, and disposable towels for employees to clean their work surfaces
  • Provide appropriate disposal receptacles for employees
  • Allow sick employees to stay home so they don’t spread infection to others
  • Encourage annual vaccination against influenza. Consider holding an influenza vaccination clinic at the worksite.
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