Tag: flu

How Effective Is the Flu Vaccine?

The flu vaccine works.

How well does it work?

It depends…

How Effective Is the Flu Vaccine?

What does it depend on?

“The vaccine effectiveness of seasonal influenza vaccines is a measure of how well the seasonal influenza vaccine prevents influenza virus infection in the general population during a given influenza season.”

WHO on Vaccine effectiveness estimates for seasonal influenza vaccines

Is the flu virus that is going around the same strain that was picked to be in the flu vaccine?

Once upon a time, we didn't have flu vaccines to help keep us healthy.
Once upon a time, we didn’t have flu vaccines to help keep us healthy.

Has the flu virus drifted, even if it is the same strain that is in the flu vaccine, becoming different enough that your protective flu antibodies won’t recognize it?

Is the H3N2 strain of flu virus the predominate strain during the flu season? H3N2 predominant flu seasons are thought to be worse than others.

In general, the flu vaccine is going to be less effective in a season where there is a poor match between the circulating strain of flu virus that is getting people sick and the strain that is in the flu vaccine, especially if it is an H3N2 strain that has drifted.

That’s why, since the 2004-05 season, the average flu vaccine effectiveness has been about 41%.

How Effective Is This Year’s Flu Vaccine?

It’s probably also why, every year, we seem to hear the same questions:

  • Should I get a flu vaccine? – yes, definitely
  • Will we have enough flu vaccines? – while historically there have been some delays and shortages, we have a very good supply of flu vaccine this year, between 151 to 166 million doses
  • How effective is this year’s flu vaccine???

Unfortunately, we really won’t know the answer to that last question until this year’s flu season really gets going.

What about reports that the flu vaccine effectiveness will be as low as 10% this year?

It is important to note that those reports are not based on flu activity in the United States and it has been a long time since we have seen flu vaccine effectiveness that low – the 2004-05 flu season. That was the year that because of a drifted A(H3N2) virus, “only 5% of viruses from study participants were well matched to vaccine strains.”

The 10% number is instead based on reports of Australia’s flu season, in which early estimates found that the A(H3N2) component of the flu vaccine was only 10% effective. Importantly, the overall vaccine effectiveness was much higher. Including other strains, the flu vaccine in Australia was at least 33% effective this past year.

“In the temperate regions of the Southern Hemisphere, influenza activity typically occurs during April – September.”

CDC on Influenza Prevention: Information for Travelers

Couldn’t we see a drifted A(H3N2) virus this year?

Sure, especially since an A(H3N2) virus will likely be the dominant strain, but so far “data indicate that currently circulating viruses have not undergone significant antigenic drift.”

“It is difficult to predict which influenza viruses will predominate in the 2017–18 influenza season; however, in recent past seasons in which A(H3N2) viruses predominated, hospitalizations and deaths were more common, and the effectiveness of the vaccine was lower.”

CDC on Update: Influenza Activity — United States, October 1–November 25, 2017

Again, it is too early to predict how effective the flu vaccine will be, but based on an undrifted H3N2 virus that is matched to the vaccine, you might expect an effectiveness between 30 to 40%.

It might be less if theories about egg-adapted mutations are true and are a factor this year.

“…some currently circulating A(H3N2) viruses are less similar to egg-adapted viruses used for production of the majority of U.S. influenza vaccines.”

CDC on Update: Influenza Activity — United States, October 1–November 25, 2017

It is also important to keep in mind that vaccine effectiveness numbers from Australia and the United States don’t always match up.

For example, in 2009, Australia reported an interim flu vaccine effectiveness of just 9%, but in the United States, the flu vaccine ended up being 56% effective! On the other hand, in 2014, the flu vaccine worked fairly well in Australia, but vaccine effectiveness was found to be just 19% in the United States.

Vaccine Effectiveness by Year
Australia United States
2007 60% 2007-08 37%
2008 NE 2008-09 41%
2009 7% 2009-10 56%
2010 73% 2010-11 60%
2011 48% 2011-12 47%
2012 44% 2012-13 49%
2013 55% 2013-14 52%
2014  50% 2014-15 19%
2015  ?% 2015-16 48%
2016  ?% 2016-17 42%
2017 33% 2017-18 ?%

What does all of this mean?

Not much.

“This season’s flu vaccine includes the same H3N2 vaccine component as last season, and most circulating H3N2 viruses that have been tested in the United States this season are still similar to the H3N2 vaccine virus. Based on this data, CDC believes U.S. VE estimates from last season are likely to be a better predictor of the flu vaccine benefits to expect this season against circulating H3N2 viruses in the United States. This is assuming minimal change to circulating H3N2 viruses. However, because it is early in the season, CDC flu experts cannot predict which flu viruses will predominate. Estimates of the flu vaccine’s effectiveness against circulating flu viruses in the United States will be available later in the season.”

CDC on Frequently Asked Flu Questions 2017-2018 Influenza Season

The reports about what happened in Australia should not have made headlines beyond Australia.

As you should get your family vaccinated if you haven’t yet.

The Flu Vaccine Works

Getting a flu vaccine has many benefits with few risks and can:

  • reduce your chances of getting the flu
  • reduce the chances that your newborn gets the flu if you get your flu shot while pregnant
  • lead to milder symptoms if you do get the flu
  • reduce your risk of being hospitalized
  • reduce your risk of dying from the flu

And while it isn’t perfect, getting a flu vaccine is certainly better than remaining unprotected and simply taking your chances that you won’t get the flu and complications from the flu.

What to Know About Flu Vaccine Effectiveness

Although the effectiveness of the flu vaccine varies from year to year, depending on how well matched the vaccine is to circulating flu virus strains, which strains are dominant, and whether they have drifted, it is always a good idea to get vaccinated and protected.

More on Flu Vaccine Effectiveness

This Year’s Flu Season

Breaking News: Flu season has started. (see below)

Flu activity continues to increase across the United States.
Flu activity continues to increase across the United States.

While flu season typically peaks in February, it is very important to understand that there are few things that are typical about the flu.

Since 1982, while we have been twice as likely to see a flu activity peak in February than other winter months, we have been just as likely to get that peak in December, January, or March. That makes it important to get your flu vaccine as soon as you can.

You really never know if it is going to be an early, average, or late flu season.

Flu Facts

While there will likely be some surprises this flu season – there always are – there are some things that you can unfortunately count on.

Among these flu facts include that:

  • there have been over 1,600 pediatric flu deaths since the 2003-04 flu season, including 110 flu deaths last year
  • about 113 kids die of the flu each year – most of them unvaccinated
  • antiviral flu medicines, such as Tamiflu, while recommended to treat high-risk people, including kids under 2 to 5 years of age, have very modest benefits at best (they don’t do all that much, are expensive, don’t taste good, and can have side effects, etc.)
  • a flu vaccine is the best way to decrease your child’s chances of getting the flu

And even in a mild flu season, a lot of kids get sick with the flu.

This Year’s Flu Season

When does flu season start?

In general, flu season starts when you begin to see people around you with signs and symptoms of the flu, including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, and fatigue, etc. To be more accurate, you can also look at reports for flu activity in your area, especially the weekly reports from the CDC. Those flu reports can also help you determine when flu season ends.

As of early December, the CDC again reported that “flu activity increased  slightly in the United States.”

Are we in store for an early flu season this year? It sure seems that way.

The CDC has also recently reported that:

  • seven states are already reporting widespread flu activity – Arkansas, Georgia, Louisiana, Massachusetts, Mississippi, Oklahoma, and Virginia
  • 18 states are now reporting regional flu activity  – Alabama, Alaska, Arizona, California, Colorado, Connecticut, Florida, Illinois, Kentucky, Maine, Missouri, New Hampshire, New York, North Dakota, Ohio, South Carolina, Texas, and Washington
  • 18 states are still reporting local flu activity – Hawaii, Idaho, Indiana, Kansas, Maryland, Michigan, Minnesota, Montana, Nebraska, New Jersey, New Mexico, North Carolina, Oregon, Pennsylvania, South Dakota, Tennessee, Wisconsin, and Wyoming
  • only 7 states are still reporting sporadic flu activity – Delaware, Iowa, Nevada, Rhode Island, Utah, Vermont, and West Virginia
  • no states have no flu activity anymore
  • between 151 to 166 million doses of flu vaccine will be available this year, including 130 million doses of thimerosal-free or preservative-free flu shots, so the great majority of flu shots will not contain mercury!
  • we still won’t have a nasal spray flu vaccine in the US this year, even though it is working well in other countries
  • although it is too early to tell how well the flu vaccine will work, it is good news that “The majority of the influenza viruses collected from the United States during October 1 through December 2, 2017 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2017–18 Northern Hemisphere influenza vaccine viruses.”
  • there has already been seven pediatric flu deaths this year, including two new pediatric deaths this past week

Have you and your family gotten been vaccinated and protected against the flu yet?

“CDC recommends that everyone 6 months and older get an injectable flu vaccine as soon as possible.”

CDC Influenza Situation Update

If not, this a great time to get a flu vaccine.

Recent Flu Seasons

Are H3N2 predominant flu seasons really worse than others?

  • 2003-04 flu season – 152 pediatric flu deaths (H3N2-predominant)
  • 2004-05 flu season – 47 pediatric flu deaths
  • 2005-06 flu season – 46 pediatric flu deaths
  • 2006-07 flu season – 77 pediatric flu deaths
  • 2007-08 flu season – 88 pediatric flu deaths (H3N2-predominant)
  • 2008-09 flu season – 137 pediatric flu deaths
  • 2009-10 flu season – 289 pediatric flu deaths (swine flu pandemic)
  • 2010-11 flu season – 123 pediatric flu deaths
  • 2011-12 flu season – 37 pediatric flu deaths
  • 2012-13 flu season – 171 pediatric flu deaths (H3N2-predominant)
  • 2013-14 flu season – 111 pediatric flu deaths
  • 2014-15 flu season – 148 pediatric flu deaths (H3N2-predominant)
  • 2015-16 flu season – 92 pediatric flu deaths
  • 2016-17 flu season – 110 pediatric flu deaths (H3N2-predominant)

In addition to high levels of pediatric flu deaths, the CDC reports that the four flu seasons that were H3N2-predominant in recent years were “the four seasons with the highest flu-associated mortality levels in the past decade.”

For More Information on the 2017-18 Flu Season

Updated December 10, 2017

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