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Posts Tagged ‘flu vaccine effectiveness’

Flu Vaccine Benefits Go Beyond Effectiveness of One Strain

December 11, 2017 2 comments
LJ TanGuest post by Litjen (LJ) Tan, MS, PhD; co-chair and co-founder of the National Adult and Influenza Immunization Summit.

 

There seems to be a lot of speculation recently about how effective the influenza (flu) vaccine will be at preventing cases of influenza this season.

We have heard suggestions that the vaccine may only be 10% effective against flu this year, that there may be mismatches in the vaccine compared to the influenza strains that are circulating, and thus, that the vaccine is not worth getting.

To address these concerns I will start with a basic explanation of flu and flu vaccines, and then discuss the factors that play into vaccine effectiveness.

First, let me say that influenza is a serious respiratory infection that is responsible for about 30% of all the respiratory infections during the winter season. When I say serious, I mean that flu can keep you down for a week or more, and you will feel completely miserable. Additionally, each year thousands of people of all ages die from flu in the U.S.; it can be very dangerous. So, that office colleague who said that he was out with the flu yesterday very likely did not have influenza. Not fully understanding the dangers of flu is why some people fail to see the value of flu prevention.  

Flu is caused by multiple strains of influenza viruses that circulate during the winter season; specifically, we have influenza type A (with the H3N2 and H1N1 strains) and influenza type B (there are two type B strains that can circulate and currently 90% appear to be the Yamagata lineage, but since it is still so early in the season and sample sizes are small, this data point may not be statistically significant). Because these strains of flu viruses can switch every season in terms of dominance, and can also mutate, manufacturers need to develop a new influenza vaccine every year and people need to be re-vaccinated each year.

To be clear, the vaccine development process is the same every year, it is just that the starting, or “seed”, vaccine virus that we immunize against has to be identified before it can be used to develop our country’s annual vaccines.

When that seed virus is identified, it is then amplified (or passaged) to develop more seed virus. Then that seed virus is further amplified to create the large quantities of vaccine virus that we ultimately need to prepare an adequate supply of vaccines to protect our population. That amplification of the seed virus, and the making of large amounts of vaccine virus, can occur in eggs, which is the more traditional way, or it can also occur in cell cultures. So there needs to be four seed viruses developed and amplified to create influenza vaccines – an H3N2 seed, an H1N1 seed, and the two B seed viruses.

So why do we keep hearing people say that this year’s flu vaccine may only be 10% effective? Where did that suggestion come from?

When we say that a flu vaccine is 10% effective, what we usually mean is that it was effective in preventing 10% of cases of influenza in those who were vaccinated. This 10% number that you may have heard is actually a data point from Australia, and it’s not against all strains of flu, but specifically against the H3N2 strain that dominated the southern hemisphere this past flu season. If you look at the Australian data for all influenza, the vaccine effectiveness goes up to 33%. Agreed, that’s not great for Australians (although, it’s still better than no protection), but is looking at the Australian data truly reflective of what might happen in the US?

It’s unlikely, and here’s why. Read more…

What Signals the Start of Flu Season?

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One might think that flu season starts with the arrival of vaccine in the local pharmacy or provider’s office.  Others might believe that flu season in the U.S. begins with the first case of lab verified flu.  While flu viruses are most common during the fall and winter months,  influenza activity can begin as early as September or October and last as late as May.

The CDC monitors certain key flu indicators (like outpatient visits of influenza-like illness, lab results and reports of flu hospitalizations and deaths). When these indicators rise and remain elevated for a number of consecutive weeks, than “flu season” is said to have begun.

In preparation for flu season, the Centers for Disease Control and Prevention (CDC) and the National Foundation for Infectious Diseases (NFID) kick off their annual flu vaccine campaign each September with a special press conference which emphasizes the importance of flu vaccination.

The reality is that influenza is difficult to predict. No one knows when it will peak, how many people will suffer or die, or even how effective the flu vaccine will be.

However, what experts do know is that the flu is inevitable, yet preventable.  Every year there is suffering, hospitalizations and even deaths, but much of that could be prevented if more people were protected through annual vaccination.  2017 Flu News LBE

 

Flu is a fickle and unpredictable virus. 

This was the message Dr. Bill Schaffner delivered during the news conference last week.  Since 2010, flu-related hospitalizations in the U.S. typically range from 140,000 to 710,000 each year, killing between 12,000 and 56,000 people each year.  While the exact number may differ drastically from year to year, this just highlights how dangerous and unpredictable influenza is.

Now is the ideal time to get a flu shot. You want to be vaccinated weeks before possible exposure, because it can take about two weeks post-vaccination for your body to build the proper immune response from the vaccine.

Everyone should consider flu vaccination – even healthy individuals.

Flu Fact of the Week

The flu vaccine is recommended for everyone 6 months and older.  It not only helps to reduce the risk of flu illness and serious complications for the person getting vaccinated, but it also helps to reduce the amount of flu circulating in the community.  By reducing the incidence of flu, we can help protect those who might be more susceptible to serious flu illness, such as young infants too young to get vaccinated, pregnant women and older individuals who may be more susceptible to flu infection, and individuals with certain medical conditions, like heart disease, asthma and diabetes, who are at increased risk of complications from flu.

Too often people mistakenly believe that if they are healthy they don’t need a flu vaccine.  Or, they don’t realize how dangerous the flu can be and consider it akin to a bad cold.  However, influenza is a contagious respiratory illness with no cure.  Once the virus takes hold, all we can do is treat the symptoms.  While antiviral drugs are recommended to try to lessen symptoms and shorten the time one is stick by a day or two, the reality is that influenza must run it’s course.  This is why Dr. Northrop could do nothing but watch while his otherwise healthy adult sister succumbed to influenza and died.

Why choose vaccination if it can’t guarantee you won’t get flu?  

We often hear people explain that they won’t get a flu shot because it doesn’t guarantee that they won’t get the flu.  While it is true that the flu vaccine isn’t a 100% guarantee, the annual flu vaccine is  typcially about 40-60% effective.  Therefore, getting your annual flu vaccine means you will reduce your chances of getting the flu by 40% to 60% as compared to someone who does not get vaccinated. It also means that flu vaccination can significantly reduce the risk of flu-associated hospitalization and death (especially among children and older adults).

As an example, last year’s flu vaccine effectiveness was deemed to be approximately 42% effective overall.  While that may not sound overly impressive, it is estimated that flu vaccination last year prevented about 5.4 million cases, 2.7 million flu-related doctor’s visits and 86,000 hospitalizations last season.  But last year only about 46.8% of the U.S. population 6 months and older received a flu vaccine. Now imagine if more people had been vaccinated. The CDC estimates that if overall flu vaccination coverage had been just 5 percentage points higher, another 490,000 illnesses and 7,000 hospitalizations could have been prevented.

What determines flu vaccine effectiveness?  

Read more…

The 60/40 Factor and This Year’s Flu Season: It’s Not Over Yet

March 10, 2017 4 comments

It’s March, and while we may be anxious for the arrival of spring, what we’ve seen instead is a whole lot of people sick with flu.  Surveillance data shows that while the flu may have peaked in some areas of the country, flu activity remains elevated throughout most of the U.S.  Since flu season typically extends into April and May, now is the time to remain vigilant and get vaccinated if that is still something you haven’t managed to do.

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Flu surveillance reports indicate that the flu strains that make up this year’s vaccine are a good match to those circulating across the U.S.  The most dominant strain has been the influenza A (H3N2) strain, and the estimated effectiveness of the vaccine in preventing illness caused by that strain has been 43%. However, we’re also seeing cases of influenza B virus, and the vaccine’s estimated effectiveness against that strain is 73%. This amounts to an overall vaccine protection of about 48%.

While some may question, “Why get a flu shot if it doesn’t guarantee you won’t get the flu?”, the answer is simple. 48% protection is much better than none.

When a vaccinated individual is exposed to flu, they are about half as likely to have to go to the doctor, be hospitalized or even die from the flu as compared to their unvaccinated counterpart.

Sure, the flu vaccine isn’t perfect.  But that doesn’t mean it’s not worth getting.  

Consider the fact that most everyone wears a seat belt when driving in a car, and yet they’ve only been shown to reduce vehicular injury and death by about 50%.  So if you wouldn’t drive your car without wearing a seatbelt, why would you want to skip a flu shot?

Another reason people often use to explain why they haven’t gotten a flu vaccine is because they’ve never had the flu and they don’t consider it to be dangerous.

The 60/40 factor tells us otherwise.

40:  This is the number of children who’ve died from the flu so far this season.  

While no parent every imagines that their child will die from a preventable disease, we know that 40 children across the nation have died from flu so far this season. And sadly, the season is not over yet.  (Update: as of March 13th the number of pediatric deaths has risen to 48). Most years the average is closer to 100 pediatric flu deaths and as high as 49,000 flu-related deaths among adults.

Since pediatric flu deaths must be reported, as flu112315opposed to adult flu deaths, we tend to see news reports throughout the flu season, such as these: 

While we may never know the specifics of each case, what we do know is that the flu is completely unpredictable.  From season to season, we don’t always know exactly which strain will be most prevalent, which will be most dangerous, and who will suffer, be hospitalized or even die as a result of the flu.

The 60/40 factor in regards to pediatric flu deaths: In a previous season, 60% of pediatric deaths occurred among children who were in a high risk category, while 40% had no chronic health problems.

Read more…

Friday Flu Shot: CDC Provides Influenza Update

January 11, 2013 4 comments

Influenza has hit the United States early this year.  I would be surprised if you’re not already aware of this, because there is so much discussion about it these days. With all the conversations there comes a variety of accurate and inaccurate information being spread.  People are making statements about the flu shot, vaccine effectiveness, possible side effects, what constitutes “the flu”, how serious the flu is (or is not), and how many people have died.  This morning, a flu related status update on our Vaccinate Your Baby Facebook page provided a perfect example of this. I read several statements that were completely untrue.  Some people even stated that their doctors were informing them that the flu vaccine was not a good match to the strains that are circulating.  That is just completely inaccurate.

However, as more than 100 comments continued to come in on that particular thread, I turned my attention to an important conference call initiated by the CDC.  This call was scheduled to provide media with an accurate update on this year’s influenza season and it was a wonderful opportunity for people to ask questions of Tom Frieden, M.D., M.P.H., Director, Centers for Disease Control and Prevention and Joseph Bresee, M.D., Chief of the Epidemiology and Prevention Branch, Influenza Division, CDC.

I’m sure we will be reading lots of coverage of this call over the next few days.  However, since I know our readers are interested in keeping up-to-date on immunization related news, below you will find a few of the most prevalent data points released by the CDC today.

Flu Activity: Read more…