2017-2018 Flu Season FAQ

Posted on: 14th November, 2017

New Flu Information for 2017-2018

Getting an annual flu vaccine is the first and best way to protect yourself and your family from the flu. Flu vaccination can reduce flu illnesses, doctors’ visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations. In 2017, a study in Pediatrics was the first of its kind to show that flu vaccination also significantly reduced a child’s risk of dying from influenza. The more people who get vaccinated, the more people will be protected from flu, including older people, very young children, pregnant women, and people with certain long-term health conditions who are more vulnerable to serious flu complications. This page summarizes information for the 2017-2018 flu season.

What’s new this flu season?

A few things are new this season:

  • The recommendation to not use the nasal spray flu vaccine (LAIV) was renewed for the 2017-2018 season. Only injectable flu shots are recommended for use again this season.
  • Flu vaccines have been updated to better match circulating viruses (the influenza A(H1N1) component was updated).
  • Pregnant women may receive any licensed, recommended, and age-appropriate flu vaccine.
  • quadrivalent recombinant flu vaccine (“Flublok Quadrivalent” RIV) is newly available this season. (Last season, only trivalent recombinant flu vaccine was available.)
  • A quadrivalent inactivated flu vaccine, “Afluria Quadrivalent” IIV, was licensed last season after the annual recommendations were published.
  • The age recommendation for “Flulaval Quadrivalent” has been changed from 3 years old and older to 6 months and older to be consistent with FDA-approved labeling.
  • The trivalent formulation of Afluria is recommended for people 5 years and older (from 9 years and older) in order to match the Food and Drug Administration package insert.
  • For the first time, a cell-grown H3N2 vaccine reference virus was used to produce the H3N2 component of the cell-based vaccine, Flucelvax. (The remaining Flucelvax vaccine components were manufactured using egg-grown reference viruses.) For more information, see the questions: “Why is it significant that a cell-grown vaccine reference virus (H3N2) was used to produce flu vaccine?” and “Is flu vaccine made using a cell-grown reference virus and cell-based technology more effective than vaccine made using an egg-grown reference virus and egg-based technology?

What flu vaccines are recommended this season?

This season, only injectable flu vaccines (flu shots) are recommended. Some flu shots protect against three flu viruses and some protect against four flu viruses.

Options this season include:

Live attenuated influenza vaccine (LAIV) – or the nasal spray vaccine – is not recommended for use during the 2017-2018 season because of concerns about its effectiveness.

There is a table showing all the flu vaccines that are FDA-approved for use in the United States during the 2017-2018 season.

What viruses will the 2017-2018 flu vaccines protect against?

There are many different flu viruses and they are constantly changing. The composition of U.S. flu vaccines is reviewed annually and updated as needed to match circulating flu viruses. Flu vaccines protect against the three or four viruses (depending on vaccine) that research suggests will be most common. For 2017-2018, three-component vaccines are recommended to contain:

  • an A/Michigan/45/2015 (H1N1)pdm09-like virus (updated)
  • an A/Hong Kong/4801/2014 (H3N2)-like virus
  • a B/Brisbane/60/2008-like (B/Victoria lineage) virus

Quadrivalent (four-component) vaccines, which protect against a second lineage of B viruses, are recommended to be produced using the same viruses recommended for the trivalent vaccines, as well as a B/Phuket/3073/2013-like (B/Yamagata lineage) virus.

When should I get vaccinated?

You should get a flu vaccine now, if you haven’t gotten one already this season. It’s best to get vaccinated before flu begins spreading in your community. It takes about two weeks after vaccination for antibodies to develop in the body that protect against flu. CDC recommends that people get a flu vaccine by the end of October, if possible.  Getting vaccinated later, however, can still be beneficial and vaccination should continue to be offered throughout the flu season, even into January or later.

Children who need two doses of vaccine to be protected should start the vaccination process sooner, because the two doses must be given at least four weeks apart.

Can I get a flu vaccine if I am allergic to eggs?

The recommendations for people with egg allergies are the same as last season.

  • People who have experienced only hives after exposure to egg can get any licensed flu vaccine that is otherwise appropriate for their age and health.
  • People who have symptoms other than hives after exposure to eggs, such as angioedema, respiratory distress, lightheadedness, or recurrent emesis; or who have needed epinephrine or another emergency medical intervention, also can get any licensed flu vaccine that is otherwise appropriate for their age and health, but the vaccine should be given in a medical setting and be supervised by a health care provider who is able to recognize and manage severe allergic conditions. (Settings include hospitals, clinics, health departments, and physician offices). People with egg allergies no longer have to wait 30 minutes after receiving their vaccine.

Why is it significant that a cell-grown vaccine reference virus (H3N2) was used to produce flu vaccine?

Cell-grown reference viruses do not have the changes that are present in egg-grown reference viruses, so they should be more similar to circulating “wild-type” viruses. Vaccine effectiveness depends in part on the match between the vaccine virus and circulating flu viruses.

Is flu vaccine made using a cell-grown reference virus and cell-based technology more effective than vaccine made using an egg-grown reference virus and egg-based technology?

While the use of cell-grown reference viruses and cell-based technology may offer the potential for better protection over traditional, egg-based flu vaccines because they result in vaccine viruses that are more similar to flu viruses in circulation, there are no data yet to support this. There is no preferential recommendation for one injectable flu vaccine over another.

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Flu Activity

What sort of flu season is expected this year?

It’s not possible to predict what this flu season will be like. While flu spreads every year, the timing, severity, and length of the season varies from one year to another.

Will new flu viruses circulate this season?

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.

Will the United States have a flu epidemic?

The United States experiences epidemics of seasonal flu each year. This time of year is called “flu season.” In the United States, flu viruses are most common during the fall and winter months. Influenza activity often begins to increase in October and November. Most of the time flu activity peaks between December and February and can last as late as May. CDC monitors certain key flu indicators (for example, outpatient visits of influenza-like illness (ILI), the results of laboratory testing and reports of flu hospitalizations and deaths). When these indicators rise and remain elevated for a number of consecutive weeks, “flu season” is said to have begun. Usually ILI increases first, followed by an increase in flu-associated hospitalizations, which is then followed by increases in flu-associated deaths.

For the most current influenza surveillance information, please see FluView at Weekly U.S. Influenza Surveillance Report.

When will flu activity begin and when will it peak?

The timing of flu is very unpredictable and can vary in different parts of the country and from season to season. Seasonal flu viruses can be detected year-round; however, seasonal flu activity often begins as early as October and November and can continue to occur as late as May. Flu activity most commonly peaks in the United States between December and February.

How many people get sick with flu every year?

The exact number of flu illnesses that occur each season is not known because flu is not a reportable disease and not everyone who gets sick with the flu seeks medical care or gets tested. CDC conducts surveillance of flu activity year round through several surveillance systems, such as the Outpatient Influenza-like Illness Surveillance Network (ILINet), which collects information on outpatient illness, and FluSurv-Net, which collects information on hospitalizations.  For more information, see CDC’s Overview of Influenza Surveillance in the United States page. However, to estimate the true burden of flu illness in the United States, including total flu cases, CDC uses mathematical modeling in combination with data from these traditional flu surveillance systems. CDC estimates that flu has resulted in between 9.2 million and 35.6 million illnesses each year in the United States since 2010.  For more information on these estimates, see CDC’s Disease Burden of Influenza page.

How many people are hospitalized from flu every year?

CDC estimates the total number of flu-associated hospitalizations in the United States. While CDC’s flu surveillance systems, such as FluSurv-NET, monitor rates of flu-associated hospitalizations in the United States, flu surveillance has limitations because most surveillance systems only capture portions of the U.S. population and in some cases can under-report severe illness, including flu hospitalizations. That is why CDC also uses mathematical modeling to fill in the picture of the disease burden. Since 2010, CDC estimates that flu has resulted in between 140,000 and 710,000 hospitalizations each year.  For more information, see CDC’s Disease Burden of Influenza page.

How many people die from flu each year?

While flu deaths in children must be reported to CDC, flu deaths in adults are not nationally notifiable. CDC uses mortality data collected by the National Center for Health Statistics to monitor relative levels of flu-associated deaths. This system tracks the proportion of death certificates processed that list pneumonia or influenza as the underlying or contributing cause of death of the total deaths reported. This system provides an overall indication of whether flu-associated deaths are elevated, but does 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.”

As it does for the numbers of flu cases, doctor’s visits and hospitalizations, CDC also estimates deaths in the United States using mathematical modeling. CDC estimates that from 2010-2011 to 2013-2014, influenza-associated deaths in the United States ranged from a low of 12,000 (during 2011-2012) to a high of 56,000 (during 2012-2013). Death certificate data and weekly influenza virus surveillance information was used to estimate how many flu-related deaths occurred among people whose underlying cause of death on their death certificate included respiratory or circulatory causes. For more information, see Estimating Seasonal Influenza-Associated Deaths in the United States and CDC’s Disease Burden of Influenza page.

Why is it difficult to know exactly how many people die from 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 flu associated deaths include the following:

  • the sheer volume of deaths to be counted;
  • the lack of testing (not everyone that dies with an influenza-like illness is tested for influenza);
  • and the different coding of deaths (influenza-associated deaths often are 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

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Protective Actions

What should I do to protect myself from flu this season?

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.

In addition to getting a seasonal flu vaccine, 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. In addition, there are prescription medications called antiviral drugs that can be used to treat influenza illness. Visit What you Should Know About Flu Antiviral Drugs for more information.

What should I do to protect my loved ones from flu this season?

Encourage your loved ones to get vaccinated. Vaccination is especially important for people at high risk for developing flu complications, and their close contacts. Also, if you have a loved one who is at high risk of flu complications and they develop flu symptoms, encourage them to get a medical evaluation for possible treatment with flu antiviral drugs. These drugs work best if given within 48 hours of when symptoms start. CDC recommends that people who are at high risk for serious flu complications and who get flu symptoms during flu season be treated with flu antiviral drugs as quickly as possible. People who are not at high risk for serious flu complications may also be treated with flu antiviral drugs, especially if treatment can begin within 48 hours.

Do some children require two doses of flu vaccine?

Yes. Some children 6 months through 8 years of age will require two doses of flu vaccine for adequate protection from flu. Children in this age group who are getting vaccinated for the first time will need two doses of flu vaccine, spaced at least 28 days apart. Children who have only received one dose in their lifetime also need two doses. Your child’s doctor or other health care professional can tell you if your child needs two doses of flu vaccine. Visit Children, the Flu, and the Flu Vaccine for more information.

What can I do to protect children who are too young to get vaccinated?

Children younger than 6 months old are at high 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 old, you should get a flu vaccine to help protect them from flu. See Advice for Caregivers of Young Children for more information. Everyone else who is around the baby also should be vaccinated. Also, studies have shown that flu vaccination of the mother during pregnancy can protect the baby after birth from flu infection for several months.

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 flu to others.

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Vaccine and Vaccination

How much flu vaccine will be available this season?

Flu vaccine is produced by private manufacturers, so supply depends on manufacturers. For the 2017-2018 season, manufacturers projected they would provide between 151 million and 166 million doses of injectable vaccine for the U.S. market. (Projections may change as the season progresses.) Flu vaccine supply updates will be provided as they become available at Seasonal Influenza Vaccine & Total Doses Distributed.

Will live attenuated intranasal influenza vaccine (LAIV) be available this season even though it is not recommended for use?

FluMist® Quadrivalent is still an FDA-licensed product. As such, there may be some supply of FluMist® Quadrivalent on the U.S. market during the 2017-2018 season. It is important for clinicians and the public to be aware that because of concerns about this vaccine’s effectiveness, CDC recommends that this vaccine not be used during the 2017-2018 influenza season.

What flu vaccine should I get instead of the nasal spray vaccine?

People who usually get the nasal spray vaccine (trade name FluMist Quadrivalent®) should get a licensed and recommended injectable flu vaccine (a flu shot) during 2017-2018. There are many different formulations of injectable flu vaccines approved for use in different people. There is a table showing all the influenza vaccines that are FDA-approved for use in the United States during the 2017-2018 season

My child usually gets the nasal spray vaccine. Can I skip getting them vaccinated since nasal spray flu vaccine is not recommended?

It is really important that you still get your child vaccinated against influenza this season. CDC, the American Academy of Pediatrics and other partners support an annual flu vaccine for children, including the use of injectable vaccines during 2017-2018. Influenza can be a serious illness for children and children (especially school-aged children) are more likely to get sick with flu. Millions of children get sick with flu every season. A typical flu illness can mean missing a week or more of school, and thousands of children are hospitalized due to flu every flu season. Once infected, children then spread flu to others. A flu shot can keep your child from getting sick with flu. Vaccinating your child also protects people around them (like grandparents, babies or anyone with long-term health problems) who are more vulnerable to flu. The nasal spray flu vaccine (trade name FluMist®) is not recommended this season because of concerns that it may not work well. More information about flu vaccination for children this season is available in “Flu Information for Parents with Young Children.”

When should I get vaccinated?

Getting vaccinated before flu activity begins helps protect you once the flu season starts in your community. It takes about two weeks after vaccination for the body’s immune response to fully respond and for you to be protected so make plans to get vaccinated. CDC recommends that people get a flu vaccine by the end of October, if possible. However, getting vaccinated later can still be beneficial. CDC recommends ongoing flu vaccination as long as influenza viruses are circulating, even into January or later. Children aged 6 months through 8 years old who need two doses of vaccine should get 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 28 days apart.

Where can I get a flu vaccine?

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.

What is flu vaccination using a jet injector?

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.

What is adjuvanted flu vaccine?

The U.S. Food and Drug Administration (FDA) licensed a new seasonal influenza (flu) vaccine containing adjuvant for adults 65 years of age and older. An adjuvant is an ingredient added to a vaccine to create a stronger immune response to vaccination. FLUAD™[155 KB, 13 pages] was licensed in November 2015 and will be available during the 2017-2018 flu season. It contains the MF59 adjuvant, an oil-in-water emulsion of squalene oil. FLUAD™ is the first adjuvanted seasonal flu vaccine marketed in the United States. For more information visit: FLUAD™ Flu Vaccine With Adjuvant.

How effective will flu vaccines be this season?

Influenza vaccine effectiveness (VE) can vary from year to year among different age and risk groups and even by vaccine type. How well the vaccine works can depend in part on the match between the vaccine virus used to produce the vaccine and the circulating viruses that season. It’s not possible to predict what viruses will be most predominant during the upcoming season. CDC monitors circulating viruses throughout the year and provides new and updated information about their similarity to the flu vaccine viruses as it becomes available. Information is published weekly in FluView and summarized at intervals in the Morbidity and Mortality Weekly Report (MMWR). Vaccine effectiveness estimates are also provided when they become available. While vaccine effectiveness can vary, recent studies show vaccine reduces the risk of flu illness by about 40% to 60% among the overall population during seasons when most circulating flu viruses are like the vaccine viruses. Similar reductions against hospitalization have been observed too. For more information about previous vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work?.

Will this season’s flu vaccine be a good match for circulating viruses?

It’s not possible to predict with certainty if the flu vaccine will be a good match for circulating flu viruses. The flu vaccine is made to protect against the flu viruses that research and surveillance indicate will likely be most common during the season. However, experts must pick which flu viruses to include in the flu vaccine many months in advance in order for flu vaccines to be produced and delivered on time. Also 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. Another factor that can impact vaccine effectiveness, especially against influenza A(H3N2) viruses, are changes that can occur in vaccine viruses as they are grown in eggs, which is the production method for most current flu vaccines. Because of these factors, there is always the possibility of a less than optimal match between circulating flu viruses and the viruses in the flu 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 flu vaccine and circulating flu viruses.

One of the ways that helps CDC evaluate the match between flu vaccine viruses and circulating flu viruses is with a lab process called ‘genetic and antigenic characterization’. Results of genetic and antigenic characterization testing are published weekly in CDC’s FluView.

How long does a flu vaccine protect me from getting the flu?

Multiple studies conducted over different seasons and across flu 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.

Getting vaccinated each year provides the best protection against the flu 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 flu vaccine have not changed for the current season.

Can the flu vaccine provide protection even if the flu vaccine is not a “good” match?

Yes, antibodies made in response to vaccination with one flu virus can sometimes provide protection against different but related flu viruses. A less than ideal match may result in reduced vaccine effectiveness against the flu virus that is different from what is in the flu vaccine, but it can still provide some protection against flu 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 flu vaccine may protect against the other flu 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.

Can I get vaccinated and still get the flu?

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.

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If You Get Sick

What happens in the body when someone has the flu?

Influenza viruses usually infect the respiratory tract (i.e., the airways of the nose, throat and lungs). As the infection increases, the body’s immune system responds to fight the virus infection. This results in inflammation that can trigger respiratory symptoms such as cough and sore throat. The immune system response can also trigger fever and cause muscle or body aches. When infected persons cough, they can spread influenza viruses in respiratory droplets to someone next to them; persons can also become infected through contact with infectious secretions or contaminated surfaces. Most people who become sick will recover in a few days to less than two weeks, but some people may become more severely ill.  Following flu infection, secondary ear and sinus infections can occur. For example, some people may develop pneumonia. This can happen to anyone, but may be more likely to happen to people who have certain chronic medical conditions, or in elderly persons.

What should I do if I get sick with the flu?

Most people with the flu have mild illness and do not need medical care or antiviral drugs. If you get sick with flu symptoms, in most cases, you should stay home and avoid contact with other people except to get medical care.

If, however, you have symptoms of flu and are in a high risk group, or are very sick or worried about your illness, contact your health care provider (doctor, physician assistant, etc.). There are drugs your doctor may prescribe for treating the flu called “antivirals.” These drugs can make you better faster and also may prevent serious complications.

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 5 years, adults 65 years of age and older, pregnant women, people with certain long-term medical conditions, and residents of nursing homes and other long-term care facilities) and people who are very sick with flu (such as those hospitalized because of flu) should get antiviral drugs. 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. Three FDA-approved antiviral medications are recommended for use during the 2017-2018 flu season: oseltamivir (available in generic versions and under the trade name Tamiflu®), zanamivir (Relenza®), and peramivir (Rapivab®). More information about antiviral drugs can be found at Treatment – Antiviral Drugs.

See “The Flu: What To Do If You Get Sick” for more information.

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Surveillance

How does CDC track flu activity?

The Epidemiology and Prevention Branch in the Influenza Division at CDC collects, compiles and analyzes information on flu activity year round in the United States and produces FluView, a weekly influenza surveillance report, and FluView Interactive, which allows for more in-depth exploration of influenza surveillance data. The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state, local, and territorial health departments, public health and clinical laboratories, vital statistics offices, healthcare providers, clinics, and emergency departments. Information in five categories is collected from eight different data sources that allow CDC to:

  • Find out when and where influenza activity is occurring
  • Track influenza-related illness
  • Determine what influenza viruses are circulating
  • Detect changes in influenza viruses
  • Measure the impact influenza is having on hospitalizations and deaths in the United States

For more information, visit “Overview of Influenza Surveillance in the United States”.

What will CDC do to monitor flu vaccine effectiveness for the 2017-2018 season?

CDC collaborates with partners each season to assess how well the seasonal flu vaccines are working. During the 2017-2018 season, CDC is planning multiple studies on the effectiveness of flu shots. These studies measure vaccine effectiveness in preventing laboratory-confirmed influenza among persons 6 months of age and older. A summary of CDC’s latest vaccine effectiveness estimates is available at Seasonal Influenza Vaccine Effectiveness, 2005-2016.

What is CDC doing to monitor antiviral resistance in the United States during the 2017-2018 season?

Antiviral resistance means that a virus has changed in such a way that antiviral drugs are less effective or not effective at all in treating or preventing illnesses with that virus. CDC will continue to collect and monitor flu viruses for changes through an established network of domestic and global surveillance systems. CDC also 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.