KidsMD Health Topics

Flu (Influenza) and H1N1

  • Overview

    Influenza, commonly know as the flu, is a highly contagious viral infection of the upper respiratory system, which includes the nose, bronchial tubes, and lungs. Because the H1N1 strain of the virus is new, your child is unlikely to have any immunity from it.

    • Between 5 and 20 percent of the U.S. population is thought to contract influenza each year
    • Symptoms include fever, muscle aches, sore throat, and a nonproductive cough.
    • Many who contract influenza will be sick for only a few days, but some have a much more serious illness and may need to be hospitalized.
    • In extreme cases, influenza can lead to pneumonia and/or death.

    How Boston Children's Hospital is helping

    At Children’s, statisticians and software developers have created HealthMap, a free Internet tool that collects data from different online sources and combines them to create a global map of different infectious disease outbreaks, categorized by disease type and location. Now, HealthMap includes the latest information on the geography of H1N1 flu outbreaks. This tool, now available as an app for iPhone and Android, has recently been updated to give users additional information on where to find flu vaccine clinics in Massachusetts.

  • What causes influenza?

    An influenza virus is generally passed from person-to-person by airborne transmission. This means your child can contract the flu by coming in contact with airborne viruses from an affected person by way of sneezing and coughing. The virus can also live for a short time on objects such as doorknobs, pens/pencils, keyboards, telephone receivers, and eating or drinking utensils, for example.

    People are generally the most contagious with the flu 24 hours before they start having symptoms; that is why it is hard to prevent the spread of the flu, especially among children, because they do not always know they are sick. The risk of infecting others usually ends around the seventh day of the infection.

    Different strains of flu

    Influenza viruses are divided into three types designated as A, B, and C. 

    • Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Efforts to control the impact of influenza are focused on types A and B.
    • Influenza type C usually causes either a very mild respiratory illness or no symptoms at all. It does not cause epidemics and does not have the severe public health impact that influenza types A and B do.
    • Novel H1N1 (referred to as "swine flu" early on) is a new influenza virus causing illness in people. This new virus was first detected in people in the United States in April 2009. For the latest information on H1N1, please visit the Boston Public Health Commission, the Massachusetts Department of Public Health and the Centers for Disease Control.

    Influenza viruses continually mutate or change, which enables the virus to evade the immune system of your child. People are susceptible to influenza infection throughout their lives. The process works as follows: 

    • A person infected with influenza virus develops antibodies against that virus.
    • The virus mutates or changes.
    • The "older" antibodies no longer recognizes the "newer" virus.
    • Reinfection occurs.

    The older antibody can, however, provide partial protection against reinfection. Currently, three different seasonal influenza viruses circulate worldwide: two type A viruses and one type B. Immunizations given each year to protect against the flu contain the influenza virus strain from each type that is expected to cause the flu within that year.

    Is the H1N1 flu more severe than seasonal flu?

    With seasonal flu, we know that seasons vary in terms of timing, duration and severity.

    • Seasonal influenza can cause mild to severe illness, and at times can lead to death.
    • Each year, in the United States, on average 36,000 people die from flu-related complications and more than 200,000 people are hospitalized from flu-related causes.
    • Of those hospitalized, 20,000 are children younger than 5 years old.
    • Over 90% of deaths and about 60 percent of hospitalization occur in people older than 65.

    When the novel H1N1 outbreak was first detected in mid-April 2009, CDC began working with states to collect information regarding the novel H1N1 flu outbreak.

    • Novel H1N1 flu has caused greater disease burden in people younger than 25 years of age than older people.
    • At this time, there are few cases and few deaths reported in people older than 64 years old, which is unusual when compared with seasonal flu.
    • Pregnancy and other previously recognized high risk medical conditions from seasonal influenza appear to be associated with increased risk of complications from this novel H1N1. These underlying conditions include asthma, diabetes, suppressed immune systems, heart disease, kidney disease, neurocognitive and neuromuscular disorders and pregnancy.

    What are the symptoms of influenza?

    Each child may experience symptoms differently, but common symptoms include:

    How is a cold different from the flu?

    A cold and the flu (influenza) are two different illnesses. A cold is relatively harmless and usually clears up by itself after a period of time, although sometimes it may lead to a secondary infection, such as an ear infection. However, the flu can lead to complications, such as pneumonia and even death. What may seem like a cold, could, in fact, be the flu. Be aware of these differences:

    Cold Symptoms Flu Symptoms
    Low or no fever High fever
    Sometimes a headache Always a headache
    Stuffy, runny nose Clear nose or stuffy nose
    Sneezing Sometimes sneezing
    Mild, hacking cough Cough, often becoming severe
    Slight aches and pains Often severe aches and pains
    Mild fatigue Several weeks of fatigue
    Sore throat Sometimes a sore throat
    Normal energy level Extreme exhaustion


    Social networks have tremendous potential to do good in the world. By leveraging existing social connections, people can spread positive health behaviors and attitudes amongst their friends and loved ones.

    Ben Reis, PhD, of the Children's Hospital Informatics Program

    Flu vaccinations

    The flu makes children and adults very ill, causing significant loss of school time and work time, and for children who have chronic diseases like asthma, it can be fatal. The larger percentage of people in the population that get vaccinated, the safer it is for everybody.

    Joanne Cox, MD, the medical director of Children's Hospital Primary Care Center

  • Most people recover from influenza within a week, but may be left feeling exhausted for as long as three to four weeks. Consult your physician in the event of more serious complications.

    Signs you need to take your child to the hospital immediately

    In children, emergency warning signs that need urgent medical attention include

    • Fast breathing or trouble breathing
    • Bluish or gray skin color
    • Not drinking enough fluids
    • Severe or persistent vomiting
    • Not waking up or not interacting
    • Being so irritable that the child does not want to be held
    • Flu-like symptoms improve but then return with fever and worse cough

    What do I do if I or my child has H1N1?

    If you live in areas where people have been identified with novel H1N1 flu and become ill with influenza-like symptoms, including fever, body aches, runny or stuffy nose, sore throat, nausea, or vomiting or diarrhea, you should stay home and avoid contact with other people.

    • CDC recommends that you stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. (Your fever should be gone without the use of a fever-reducing medicine.)
    • Stay away from others as much as possible to keep from making others sick.
    • Staying at home means that you should not leave your home except to seek medical care.
    • Avoiding normal activities, including work, school, travel, shopping, social events, and public gatherings.

    If you have severe illness or you are at high risk for flu complications, contact your health care provider or seek medical care. Your health care provider will determine whether flu testing or treatment is needed.

    CDC recommends the use of oseltamivir or zanamivir for the treatment and/or prevention of infection with the flu virus.

    • Antiviral drugs are prescription medicines (pills, liquid or an inhaled powder) that fight against the flu by keeping flu viruses from reproducing in your body.
    • If you get sick, antiviral drugs can make your illness milder and make you feel better faster.
    • They may also prevent serious flu complications.
    • During the current pandemic, the priority use for influenza antiviral drugs is to treat severe influenza illness (for example hospitalized patients) and people who are sick who have a condition that places them at high risk for serious flu-related complications.
    • In Nov. 2006, the Food and Drug Administration has warned that people who take oseltamivir should watch out for erratic behavior as a possible side effect.

    Aside from antiviral medications your doctor may prescribe, it is important to get plenty of bed rest and stay hydrated.

  • Doctors in Children’s Division of Infectious Diseases have been studying the importance of hand hygiene in preventing the spread of both respiratory and stomach viruses. Good hygiene practices have to include education on handwashing and alcohol-based hand sanitizers.

    Children’s Hospital Boston leads study about H1N1

    Usually influenzas are only fatal for people with weaker immune systems, such as infants and the elderly. During the 2009 H1N1 outbreak, several healthy children died from the disease. The study lead by Boston Children's Hospital concluded that Staphylococcus aureus (MRSA) was a contributing factor. Moreover, this suggests that co-infections can be fatal in even healthy children. Read more about theinfluenza study.


    Flu rates decline among two-to-four year olds
    Anne Gatewood Hoen and John Brownstein of Children’s Hospital Boston found that flu rates dropped 34 percent among two-to four year olds following vaccination policies in the United States, suggesting the policy was successful in reducing flu cases. Read more about this research in the Children’s newsroom.
    Antibody may protect against multiple flu types
    Stephen C. Harrison, PhD, chief of the Division of Molecular Medicine at Children’s Hospital Boston discovered an antibody, called CH65, which may provide protection against multiple variations of the influenza virus. Learn more about the CH65 antibody in the Children’s newsroom.


    Flu and asthma
    Dale Umetsu, MD, PhD, of Children’s Division of Immunology led research suggesting that targeting a compound called IL-33 may break the link between flu and asthma. IL-33 is produced while somebody has a flu, and activates natural helper cells which can induce asthma. This research may lead a path to therapy that will target the IL-33 so when patients catch the flu, it won’t trigger asthma. Learn more about this research in the Children’s newsroom.


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