What You Should Know for the 2015-2016 Influenza Season
It’s not possible to predict what this flu season will be like. Flu seasons are unpredictable in a number of ways. While flu spreads every year, the timing, severity, and length of the season varies from one year to another.
Flu viruses are constantly changing so it's not unusual for new flu viruses to appear each year. For more information about how flu viruses change, visit How the Flu Virus Can Change.
The United States experiences epidemics of seasonal flu each year. This time of year is called "flu season." In the United States, flu season occurs in the winter; flu outbreaks can happen as early as October and can last as late as May. CDC says the flu season begins when certain key flu indicators (for example, levels of influenza-like illness (ILI), hospitalization and deaths) rise and remain elevated for a number of consecutive weeks. Usually ILI increases first, followed by an increase in hospitalizations, which is then followed by increases in flu-associated deaths.
The timing of flu is very unpredictable and can vary in different parts of the country and from season to season. Most seasonal flu activity typically occurs between October and May. Flu activity most commonly peaks in the United States between December and February.
CDC recommends a yearly flu vaccine for everyone 6 months of age and older as the first and most important step in protecting against this serious disease. People should begin getting vaccinated soon after flu vaccine becomes available, ideally by October, to ensure that as many people as possible are protected before flu season begins. However, as long as flu viruses are circulating in the community, it’s not too late to get vaccinated.
In addition to getting a seasonal flu vaccine if you have not already gotten vaccinated, you can take everyday preventive actions like staying away from sick people and washing your hands to reduce the spread of germs. If you are sick with flu, stay home from work or school to prevent spreading flu to others.
Antiviral drugs are prescription drugs that can be used to treat flu illness. People at high risk of serious flu complications (such as children younger than 2 years, adults 65 and older, pregnant women, and people with certain medical conditions) and people who are very sick with flu (such as those hospitalized because of flu) should get antiviral drugs. Some other people can be treated with antivirals at their health care professional’s discretion. Treating high risk people or people who are very sick with flu with antiviral drugs is very important. Studies show that prompt treatment with antiviral drugs can prevent serious flu complications. Prompt treatment can mean the difference between having a milder illness versus very serious illness that could result in a hospital stay.
Treatment with antivirals works best when begun within 48 hours of getting sick, but can still be beneficial when given later in the course of illness. Antiviral drugs are effective across all age-and risk groups. Studies show that antiviral drugs are under-prescribed for people who are at high risk of complications who get flu. This season, three FDA-approved influenza antiviral drugs are recommended for use in the United States: oseltamivir, zanamivir and peramivir.
Encourage your loved ones to get vaccinated. Vaccination is especially important for people at high risk for serious flu complications, and their close contacts. Also, if you have a loved one who is at high risk of flu complications and who develops flu symptoms, encourage him or her to get a medical evaluation. He or she might need treatment with influenza antiviral drugs. CDC recommends that people who are at high risk for serious flu complications who get the flu be treated with influenza antiviral drugs as quickly as possible. People who are not at high risk for serious flu complications who get the flu may be treated with influenza antiviral drugs at their doctor’s discretion. Children between 6 months and 8 years of age may need two doses of flu vaccine to be fully protected from flu. The two doses should be given at least 4 weeks apart. Your child’s doctor or other health care professional can tell you whether your child needs two doses. If your child does need two doses of vaccine to be fully protected, it is a good idea to begin the vaccination process sooner rather than later. Visit Children, the Flu, and the Flu Vaccine for more information.
Children younger than 6 months are at higher risk of serious flu complications, but are too young to get a flu vaccine. Because of this, safeguarding them from flu is especially important. If you live with or care for an infant younger than 6 months of age, you should get a flu vaccine to help protect them from flu. See Advice for Caregivers of Young Children for more information.
In addition to getting vaccinated, you and your loved ones can take everyday preventive actions like staying away from sick people and washing your hands to reduce the spread of germs. If you are sick with flu, stay home from work or school to prevent spreading influenza to others.
CDC recommends that people get vaccinated against flu soon after vaccine becomes available, preferably by October.
It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against the flu.
Doctors and nurses are encouraged to begin vaccinating their patients soon after vaccine becomes available, preferably by October so as not to miss opportunities to vaccinate. Those children aged 6 months through 8 years who need two doses of vaccine should receive the first dose as soon as possible to allow time to get the second dose before the start of flu season. The two doses should be given at least four weeks apart.
A number of different private sector vaccine manufacturers produce flu vaccine for use in the United States. This season both trivalent (three component) and quadrivalent (four component) influenza vaccines will be available. Different routes of administration are available for flu vaccines, including intramuscular, intradermal, jet injector and nasal spray vaccine.
- Intramuscular (IM) vaccines will be available in both trivalent and quadrivalent formulations. (High dose vaccines, which are IM vaccines, will all be trivalent this season.)
- For people who are 18 through 64 years old, a jet injector can be used for delivery of one particular trivalent flu vaccine (AFLURIA® by bioCSL Inc.).
- Nasal spray vaccines will all be quadrivalent this season.
- Intradermal vaccine will all be quadrivalent.
Flu vaccine is produced by private manufacturers, so supply depends on manufacturers. For this season, manufacturers have projected they will provide between 164.5 and 173.5 million doses of vaccine for the U.S. market. (Projections may change as the season progresses.)
The timing of vaccine availability depends on when production is completed. If everything goes as indicated by manufacturers, shipments may begin as early as July or August and continue throughout September and October until all of the vaccine is distributed.
Flu vaccines are offered by many doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even by some schools.
Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or work.
Visit the HealthMap Vaccine Finder to locate where you can get a flu vaccine.
Recommendations on the control and prevention of influenza are published annually, in late summer or early fall. Recommendations for the 2015-2016 season will be made available in a Morbidity and Mortality Weekly Report (MMWR). During the 2014-2015 flu season, CDC recommended use of the nasal spray vaccine (LAIV) for healthy* children 2 through 8 years of age, when it was immediately available and if the child had no contraindications or precautions to that vaccine. For more information, see Nasal Spray Flu Vaccine in Children 2 through 8 Years Old or the 2014-2015 MMWR Influenza Vaccine Recommendations. However, on February 26, 2015, the Advisory Committee on Immunization Practices (ACIP) did not renew the preferential recommendation for LAIV for the 2015-2016 season. The ACIP recommendations must be approved by the CDC Director at which point they are published in the MMWR and become CDC policy. More information on this vote is available at the CDC Newsroom.
(*“Healthy” in this instance refers to children 2 years through 8 years old who do not have an underlying medical condition that predisposes them to influenza complications.)
Visit What’s New on this Site to sign up and receive updates from the CDC Influenza site.
Flu vaccines are designed to protect against the main flu viruses that research suggests will be the most common during the upcoming season. Three kinds of flu viruses commonly circulate among people today: influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses.
All of the 2015-2016 influenza vaccine is made to protect against the following three viruses:
- an A/California/7/2009 (H1N1)pdm09-like virus
- an A/Switzerland/9715293/2013 (H3N2)-like virus
- a B/Phuket/3073/2013-like virus. (This is a B/Yamagata lineage virus)
Some of the 2015-2016 flu vaccine is quadrivalent vaccine and also protects against an additional B virus (B/Brisbane/60/2008-like virus). This is a B/Victoria lineage virus.
Vaccines that give protection against three viruses are called trivalent vaccines. Vaccines that give protection against four viruses are called quadrivalent vaccines.
More information about influenza vaccines is available at Preventing Seasonal Flu With Vaccination.
On August 14, 2014, the U.S. Food and Drug Administration (FDA) approved use of one jet injector device (the PharmaJet Stratis 0.5ml Needle-free Jet Injector) for delivery of one particular flu vaccine (AFLURIA® by bioCSL Inc.) in people 18 through 64 years of age. A jet injector is a medical device used for vaccination that uses a high-pressure, narrow stream of fluid to penetrate the skin instead of a hypodermic needle. For more information, see Flu Vaccination by Jet Injector.
Influenza vaccine effectiveness (VE) can vary from year to year and among different age and risk groups. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work?
Multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time. The decline in antibodies is influenced by several factors, including the antigen used in the vaccine, the age of the person being vaccinated, and the person's general health (for example, certain chronic health conditions may have an impact on immunity). When most healthy people with regular immune systems are vaccinated, their bodies produce antibodies and they are protected throughout the flu season, even as antibody levels decline over time. Older people and others with weakened immune systems may not generate the same amount of antibodies after vaccination; further, their antibody levels may drop more quickly when compared to young, healthy people.
For everyone, getting vaccinated each year provides the best protection against influenza throughout flu season. It’s important to get a flu vaccine every season, even if you got vaccinated the season before and the viruses in the vaccine have not changed for the current season.
It's not possible to predict with certainty if the vaccine will be a good match for circulating viruses. The vaccine is made to protect against the flu viruses that research indicates will likely be most common during the season. However, experts must pick which viruses to include in the vaccine many months in advance in order for vaccine to be produced and delivered on time. And flu viruses change constantly (called drift) – they can change from one season to the next or they can even change within the course of one flu season. Because of these factors, there is always the possibility of a less than optimal match between circulating viruses and the viruses in the vaccine.
Over the course of the flu season, CDC studies samples of circulating flu viruses to evaluate how close a match there is between viruses used to make the vaccine and circulating viruses.
One of the ways that helps CDC evaluate the match between vaccine viruses and circulating viruses is with a lab process called ‘antigenic characterization.’ Results of antigenic characterization testing are published weekly in CDC’s FluView.
Yes, antibodies made in response to vaccination with one flu virus can sometimes provide protection against different but related viruses. A less than ideal match may result in reduced vaccine effectiveness against the virus that is different from what is in the vaccine, but it can still provide some protection against influenza illness.
In addition, it's important to remember that the flu vaccine contains three or four flu viruses (depending on the type of vaccine you receive) so that even when there is a less than ideal match or lower effectiveness against one virus, the vaccine may protect against the other viruses.
For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend flu vaccination for everyone 6 months and older. Vaccination is particularly important for people at high risk for serious flu complications, and their close contacts.
Yes. It’s possible to get sick with the flu even if you have been vaccinated (although you won’t know for sure unless you get a flu test). This is possible for the following reasons:
- You may be exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with flu before the vaccine begins to protect you. (About 2 weeks after vaccination, antibodies that provide protection develop in the body.)
- You may be exposed to a flu virus that is not included in the seasonal flu vaccine. There are many different flu viruses that circulate every year. The flu vaccine is made to protect against the three or four flu viruses that research suggests will be most common.
- Unfortunately, some people can become infected with a flu virus the flu vaccine is designed to protect against, despite getting vaccinated. Protection provided by flu vaccination can vary widely, based in part on health and age factors of the person getting vaccinated. In general, the flu vaccine works best among healthy younger adults and older children. Some older people and people with certain chronic illnesses may develop less immunity after vaccination. Flu vaccination is not a perfect tool, but it is the best way to protect against flu infection.
CDC collaborates with other partners each season to assess how well the seasonal vaccines are working. During the 2015-2016 season, CDC is planning multiple studies on the effectiveness of both the flu shot and the nasal-spray flu vaccine. These studies measure vaccine effectiveness in preventing laboratory-confirmed influenza among persons 6 months of age and older. CDC's seasonal influenza vaccine effectiveness estimates since 2005 are listed on the CDC website.
Information about flu vaccine supply is available here: Seasonal Influenza Vaccine & Total Doses Distributed
Yes. If you get sick, there are drugs that can treat flu illness. They are called antiviral drugs and they can make your illness milder and make you feel better faster. They also can prevent serious flu-related complications, like pneumonia. For more information about antiviral drugs, visit Treatment (Antiviral Drugs).
Antiviral resistance means that a flu virus has changed in such a way that antiviral drugs are less effective. Samples of flu viruses collected from around the United States and worldwide are studied at CDC to determine if they are becoming resistant to any of the FDA-approved influenza antiviral drugs.
CDC is continuing to collect and monitor flu viruses for changes through an established network of domestic and global surveillance systems. Additionally, CDC is working with the state public health departments and the World Health Organization to collect additional information on antiviral resistance in the United States and worldwide. The information collected will assist in making informed recommendations regarding use of antiviral drugs to treat influenza.
Unlike flu deaths in children, flu deaths in adults are not nationally reportable, and therefore, CDC cannot say how many adults die from flu each year. However, CDC has two flu surveillance systems that are used to monitor relative levels of flu-associated deaths. One is the “122 Cities Mortality Reporting System” and the other is mortality data collected by the National Center for Health Statistics. Both of these systems track the proportion of death certificates processed that list pneumonia or influenza (P&I) as the underlying or contributing cause of death of the total deaths reported. These systems provide an overall indication of whether flu-associated deaths are elevated, but do not provide an exact number of how many people died from flu. For more information, see Overview of Influenza Surveillance in the United States, “Mortality Surveillance.”
CDC also uses modeling studies to estimate numbers of flu-related deaths, but these studies apply only to past seasons and are not done each year. For more information, see Estimating Seasonal Influenza-Associated Deaths in the United States: CDC Study Confirms Variability of Flu.
There are several factors that make it difficult to determine accurate numbers of deaths caused by flu regardless of reporting. Some of the challenges in counting influenza-associated deaths include the following: the sheer volume of deaths to be counted; not everyone that dies with an influenza-like illness is tested for influenza; and influenza-associated deaths are often a result of complications secondary to underlying medical problems, and this may be difficult to sort out. For more information, see Estimating Seasonal Influenza-Associated Deaths in the United States: CDC Study Confirms Variability of Flu.
Influenza is a respiratory disease that is spread primarily from person to person through coughs and sneezes. Ebola virus is not a respiratory disease and is only spread through direct contact with blood or body fluids of a person who is sick with Ebola.
Seasonal influenza and Ebola virus infection can cause some similar symptoms. However, of these viruses, your symptoms are most likely caused by seasonal influenza. Influenza is very common. Millions of people are infected, hundreds of thousands are hospitalized and thousands die from flu each year. In the United States, fall and winter is the time for flu. While the exact timing and duration of flu seasons vary, outbreaks often begin in October and can last as late as May. Most of the time flu activity peaks between December and February. Information about current levels of U.S. flu activity is available in CDC’s weekly FluView report.
In the United States, infections with Ebola virus have been exceedingly uncommon. There is widespread transmission of Ebola virus disease in West Africa.
It is usually not possible to determine whether a patient has seasonal influenza or Ebola infection based on symptoms alone. However, there are tests to detect seasonal influenza and Ebola infection. Your doctor will determine if you should be tested for these illnesses based on your symptoms, clinical presentation and recent travel or exposure history. (For information regarding the signs and symptoms of Ebola, and whether you may need to be tested, please review the Ebola case definitions.)
Seasonal influenza and MERS can cause similar respiratory symptoms. However, of these viruses, your symptoms are most likely caused by seasonal influenza. In the United States, fall and winter is the time for flu. While the exact timing and duration of flu seasons vary, flu outbreaks often begin in October and can last as late as May. Most of the time flu activity peaks between December and February. Information about current levels of flu activity is available in CDC’s weekly FluView report.
MERS is not common in the United States. However, in 2014, two people who recently traveled from Saudi Arabia to the United States had MERS. All MERS cases have been linked to countries in or near the Arabian Peninsula.
It is not possible to determine whether a patient has seasonal influenza, or MERS, or an illness due to another pathogen based on symptoms alone. However, there are tests to detect seasonal influenza and MERS. Your doctor will determine if you should be tested for any of these illnesses based on your symptoms, clinical presentation and recent travel history. (For information regarding the signs and symptoms of MERS, and whether you may need to be tested, please review the MERS case definitions.)