• Introduction:

    Influenza (flu) is a contagious disease that can be serious. Every year, millions of people get sick, hundreds of thousands are hospitalized, and thousands to tens of thousands of people die from flu. The flu reports are created by Public Health’s epidemiology program and are designed to provide current and historical information about the flu in our community. These reports are used by Public Health programs, healthcare providers, local governments, and community partners to help inform their decision-making process when it comes to improving health outcomes.

Influenza (flu) Reports

Influenza (flu) is a contagious disease that can be serious. Every year, millions of people get sick, hundreds of thousands are hospitalized, and thousands to tens of thousands of people die from flu. The flu reports are created by Public Health’s epidemiology program and are designed to provide current and historical information about the flu in our community. These reports are used by Public Health programs, healthcare providers, local governments, and community partners to help inform their decision-making process when it comes to improving health outcomes.

Taking Temperature

Vaccination is the Best Way to Protect Yourself

Getting a flu shot not only helps protect you, it also helps protect others who may be at risk of complications from the flu,” said Public Health’s Medical Director, Becky Thomas, MD. “People with weakened immune systems, the elderly and the young are particularly at risk of flu complications.”

After two years with reduced flu numbers due to COVID precautions, Montgomery County is experiencing very high number of influenza cases and hospitalizations. This year's available flu vaccines appear well matched for the circulating flu strains. Protect yourself and others by getting vaccinated against influenza.

What is Influenza (Flu)?

Flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to death. The best way to prevent flu is by getting a flu vaccine each year.

Flu Symptoms

Influenza (flu) can cause mild to severe illness, and at times can lead to death. Flu is different from a cold. Flu usually comes 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.
*It’s important to note that not everyone with flu will have a fever.

How Flu Spreads

Most experts believe that flu viruses spread mainly by tiny droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose or possibly their eyes.

How Many People Get Sick with Flu Every Year?

A 2018 CDC study published in Clinical Infectious Diseases looked at the percentage of the U.S. population who were sickened by flu using two different methods and compared the findings. Both methods had similar findings, which suggested that on average, about 8% of the U.S. population gets sick from flu each season, with a range of between 3% and 11%, depending on the season.

Who is most likely to be infected with influenza?

The same CID study found that children are most likely to get sick from flu and that people 65 and older are least likely to get sick from influenza. Median incidence values (or attack rate) by age group were 9.3% for children 0-17 years, 8.8% for adults 18-64 years, and 3.9% for adults 65 years and older. This means that children younger than 18 are more than twice as likely to develop a symptomatic flu infection than adults 65 and older.

How is seasonal incidence of influenza estimated?

Influenza virus infection is so common that the number of people infected each season can only be estimated. These statistical estimations are based on CDC-measured flu hospitalization rates that are adjusted to produce an estimate of the total number of influenza infections in the United States for a given flu season.

The estimates for the number of infections are then divided by the census population to estimate the seasonal incidence (or attack rate) of influenza.

Does seasonal incidence of influenza change based on the severity of flu season?

Yes. The proportion of people who get sick from flu varies. A paper published in CID found that between 3% and 11% of the U.S. population gets infected and develops flu symptoms each year. The 3% estimate is from the 2011-2012 season, which was an H1N1-predominant season classified as being of low severity. The estimated incidence of flu illness during two seasons was around 11%; 2012-2013 was an H3N2-predominant season classified as being of moderate severity, while 2014-2015 was an H3N2 predominant season classified as being of high severity.

Flu FAQ

Influenza (flu) Frequently Asked Questions

ALL persons 6 months of age and older should be vaccinated. Persons especially at risk include the elderly, those with chronic illness, infants, and pregnant women. Health care workers, caregivers of high-risk individuals, and persons with contact with infants younger than 6 months are also strongly encouraged to be vaccinated.

Public Health offers preservative free quadrivalent and high-dose influenza vaccine.

No! The flu is far more dangerous, even in healthy people.

Although many people with influenza have mild illness, every year some people become very sick and need to be hospitalized, or even die. Getting a flu vaccine is the best protection against the flu and these serious complications.

No! The flu vaccine cannot give you the flu.

Flu vaccines may cause mild muscle aches and a low fever. These discomforts are brief and are signs that the vaccine is teaching your body how to protect itself against the flu. If you are exposed to the flu after vaccination, your body will be better prepared to fight the virus, and you will be less likely to become very sick and be hospitalized.

One of the following may have happened:

  • A different virus may be going around. The flu vaccine protects against common types of the flu. It does not protect against other infections like COVID-19.
  • You may have become sick with the flu before the vaccine had time to work. It takes about two weeks to be fully protected from the flu after vaccination.
  • No vaccine is 100% effective. However, if you do get the flu after vaccination, you are less likely to become seriously ill.

Yes! Protection from last year’s vaccine wears off with time, so you will need another dose of vaccine to protect yourself this year.

Flu viruses also change over time. The vaccine you receive this year will provide the best protection against the most likely types of flu viruses you may be exposed to in the community.

Yes! Flu vaccines have been around for over 50 years.

The production and safety of flu vaccines are closely monitored by the CDC and the FDA. According to the CDC, hundreds of millions of flu vaccines have been given safely.

Yes! The flu vaccine can be administered during the same visit as COVID-19 vaccines or boosters.

Different injection sites will be used to administer the vaccines. The flu vaccine will provide protection against the flu virus, and the COVID vaccine will provide protection against the virus that causes COVID-19 infections.

No! Flu seasons are unpredictable.

They can begin in early fall and last into spring. It’s never too late to protect yourself, your family and friends, and your community!

Table 1. Estimates of the Incidence of Symptomatic Influenza by Season and Age-Group, United States, 2010–2016

SeasonPredominant Virus(es)Season SeverityIncidence, %, by Age Group
0-4 yrs5-17 yrs18-49 yrs50-64 yrs≥65 yrsAll Ages
2010-11 A/H3N2, A/H1N1pdm09 Moderate 14.1 8.4 5.3 8.1 4.3 6.8
2011-12 A/H3N2 Low 4.8 3.6 2.5 3.1 2.3 3.0
2012-13 A/H3N2 Moderate 18.6 12.7 8.9 14.3 9.9 11.3
2013-14 A/H1N1pdm09 Moderate 12.4 7.2 9.2 13.0 3.4 9.0
2014-15 A/H3N2 High 150 12.7 7.8 12.9 12.4 10.8
2015-16 A/H1N1pdm09 Moderate 11.1 7.4 7.1 11.0 3.5 7.6
Median     13.2 7.9 7.4 12.0 3.9 8.3

Period of Contagiousness

You may be able to spread flu to someone else before you know you are sick, as well as while you are sick.

  • People with flu are most contagious in the first 3-4 days after their illness begins.
  • Some otherwise healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick.
  • Some people, especially young children, and people with weakened immune systems, might be able to infect others for an even longer time.

Onset of Symptoms

The time from when a person is exposed and infected with flu to when symptoms begin is about 2 days but can range from about 1 to 4 days.

Complications of Flu

Complications of flu can include bacterial pneumonia, ear infections, sinus infections and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.

People at High Risk from Flu

Anyone can get flu (even healthy people), and serious problems related to flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and children younger than 5 years.

Preventing Seasonal Flu

The first and most important step in preventing flu is to get a flu vaccine each year. Flu vaccine has been shown to reduce flu related illnesses and the risk of serious flu complications that can result in hospitalization or even death. CDC also recommends everyday preventive actions (like staying away from people who are sick, covering coughs and sneezes and frequent handwashing) to help slow the spread of germs that cause respiratory (nose, throat, and lungs) illnesses, like flu.

Diagnosing Flu

It is very difficult to distinguish flu from other viral or bacterial respiratory illnesses based on symptoms alone. There are tests available to diagnose flu.

Treating Flu

There are influenza antiviral drugs that can be used to treat flu illness.