Tag: flu shot

Is Flu Season Starting Already?

It seems like every year we get early reports of the start of flu season.

Why?

Because a few people had positive flu tests somewhere…

Is Flu Season Starting Already?

While there are many things about the flu that are unpredictable, including when flu season will start, peak, and end, there are some things that have become rather routine.

One of the things that we have come to expect every year is folks declaring an early start to flu season.

Not surprisingly, they are usually wrong.

A few positive flu tests doesn't mean that flu season is starting early.
A few positive flu tests doesn’t mean that flu season is starting early.

So why do some folks test positive in August or September if it isn’t because flu season is starting?

“During periods when influenza activity is low and there is low influenza virus circulation among persons in the community, the positive predictive value of influenza tests is low (that is, the chance that a positive result indicates that the patient has influenza is low – consider potential for a false positive result), and the negative predictive value is high (the chance that a negative result indicates that the patient does not have influenza is high – likely true negative result ).”

CDC on the Algorithm to assist in the interpretation of influenza testing results and clinical decision-making during periods when influenza viruses are NOT circulating in the community

When flu activity is low, such as it is during the summer or early fall before flu season has really started, you have a higher chance for a false positive flu test. So even though you have cold or flu symptoms and a positive rapid flu test, you might not really have the flu. The test is falsely positive. It’s wrong.

“Influenza prevalence varies between and within seasons. On the basis of our estimates, rapid tests are of limited use when prevalence is <10%”

Grijalva et al on Accuracy and Interpretation of Rapid Influenza Tests in Children

While other, more accurate flu tests are available, they are more expensive and take longer to process and get results. And since the diagnosis of the flu is often made clinically anyway, classic flu signs and symptoms during flu season, you typically don’t need a flu test unless being admitted to the hospital or if the results will really change how you are being treated.

So how do you know when flu season has started? You will see an uptick on flu activity maps. Hopefully you will have gotten your flu vaccine by then.

While flu season usually starts in October, it is the peak that we are usually more concerned about. That’s when you are most likely to be exposed to someone and get the flu.

When does flu season usually peak?

It depends, but usually sometime between December and March, typically in February. Getting back to how unpredictable flu season can be, there have been a few times that flu season has peaked as early as October though.

How can you reduce your chances of having a false positive flu test?

That’s easy. Don’t get a flu test unless flu activity is high in your area and you have classic signs and symptoms of the flu.

More on the Start of Flu Season

Why Do You Need to Get a Flu Vaccine Each Year?

A yearly flu vaccine is the best way to protect yourself and your family against the flu.

But why do you need to get a flu vaccine each and every year?

Why Do You Need to Get a Flu Vaccine Each Year?

Hopefully we will one day have a universal flu vaccine that covers all flu strains and offers longer lasting protection.

Most folks know we don’t have that flu vaccine yet…

“A flu vaccine is needed every season for two reasons. First, the body’s immune response from vaccination declines over time, so an annual vaccine is needed for optimal protection. Second, because flu viruses are constantly changing, the formulation of the flu vaccine is reviewed each year and updated as needed to keep up with changing flu viruses. For the best protection, everyone 6 months and older should get vaccinated annually.”

CDC on Key Facts About Seasonal Flu Vaccine

So because the protection from the flu vaccine wanes or wears off relatively quickly, even if the flu vaccine strains don’t change from one year to the next, you should get a new flu vaccine.

How long does the protection from the flu vaccine last?

“An analysis from the 2011–12 through 2013–14 seasons noted protection ranging from 54% to 67% during days 0 through 180 postvaccination.”

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices—United States, 2018–19 Influenza Season

The flu vaccines takes about two weeks to become effective and should then last for at least six months – long enough to get  you through the average flu season.

“A number of observational studies and a post hoc analysis from a randomized controlled trial have reported decreases in vaccine effectiveness (VE) within a single influenza season, with increasing time postvaccination. Waning effects have not been observed consistently across age groups, virus subtypes, and seasons; and observed declines in protection could be at least in part attributable to bias, unmeasured confounding, or the late season emergence of antigenic drift variants that are less well-matched to the vaccine strain. Some studies suggest this occurs to a greater degree with A(H3N2) viruses than with A(H1N1) or B viruses . This effect might also vary with recipient age; in some studies waning was more pronounced among older adults and younger children. Rates of decline in VE have also varied.”

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices—United States, 2018–19 Influenza Season

That means it should last past the peak of the average flu season, which is typically between December and March.

And in most young, healthy people, the protection likely lasts even longer.

Make sure you are vaccinated well before flu season starts.
Make sure you are vaccinated well before flu season peaks, which since 1982 has occurred as early as October and as late as March, but is most common in February.

Still, there is some concern that the protection from the flu vaccine can wear off during a flu season, especially if you are very young, very old, or have chronic medical problems, and you get your flu vaccine early and you get exposed late – in April or May.

Of course, that’s not a good reason to delay getting a flu vaccine though, as waiting too long might leave you unprotected if flu peaks early, in October or November.

What to Know About Why You Need the Flu Vaccine Every Year

Since the flu vaccine strains can change and protection doesn’t last from season to season, get a flu vaccine each year. It’s the best way to protect yourself and your family against the flu.

More on Why You Need the Flu Vaccine Every Year

Do They Really Just Guess at Which Strain to Put in the Flu Vaccine?

Every year we hear experts telling us to get vaccinated against the flu.

And more often than not, we hear critics telling us that the flu vaccine isn’t going to work that well because it isn’t a good match.

Is that because they just guess at which flu strains to put into the flu vaccine each year, as some folks say?

Do They Really Just Guess at Which Strain to Put in the Flu Vaccine?

Of course they don’t guess at which vaccine strain to put in the flu vaccine!

“Flu viruses are constantly changing, so the vaccine composition is reviewed each year and updated as needed based on which influenza viruses are making people sick, the extent to which those viruses are spreading, and how well the previous season’s vaccine protects against those viruses.”

CDC on Selecting Viruses for the Seasonal Influenza Vaccine

There are over 100 flu centers in over 100 countries that are involved in testing thousands of flu virus samples each year. Representative samples from these centers then go to the five major World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza.

The directors of these centers review these samples and other available information and make a recommendation on which vaccine strains to include in the flu vaccine for the next flu season. Each country then considers this recommendation and decides which flu strains to include in their flu vaccine.

“The influenza viruses in the seasonal flu vaccine are selected each year based on surveillance data indicating which viruses are circulating and forecasts about which viruses are the most likely to circulate during the coming season.”

CDC on Selecting Viruses for the Seasonal Influenza Vaccine

Although they don’t have a crystal ball and so can’t know exactly which flu strains will be making us sick each flu season, it is hardly a wild guess.

How often are they right?

“During seasons when most circulating influenza viruses are closely related to the viruses in the influenza vaccine, the vaccine effectiveness estimate has ranged from 50-60% among the overall population.”

WHO on Vaccine effectiveness estimates for seasonal influenza vaccines

Actually, they are right in most years! So if it is a guess, than the folks who choose which strains to include in the flu vaccine are very good guessers!

Except for a few years when their was a poor match, the flu season is typically between 37 to 60% effective.
Except for a few years when their was a poor match, the flu season is typically between 37 to 60% effective.

There have actually only been a few times in recent years when we have had mismatched flu strains. And in one of those years, they picked the right strain, but then the strain changed or drifted before the start of flu season.

“One hundred fifty-six (22%) of the 709 influenza A(H3N2) isolates were characterized as antigenically similar to A/Wyoming/3/2003, which is the A/Fujian/411/2002-like (H3N2) component of the 2004-05 influenza vaccine, and 553 (78%) were characterized as A/California/7/2004-like.”

2004-05 U.S. Influenza Season Summary

Not surprisingly, flu vaccine effectiveness goes way down during a mismatch year. During the 2004-05 flu season, for example, the overall vaccine effectiveness of the flu vaccine was just 10%.

Of course, in most years, flu vaccine is typically much more effective than that.

How effective will flu vaccines be this season?

Will this year’s flu vaccine be a good match?

We won’t know until flu season is well under way, not that you should wait for an answer to get your flu vaccine. The benefits of the flu vaccine extend beyond preventing the flu, so it is a good idea to get vaccinated even in a year when there might not be a good match.

More on Selecting Flu Vaccine Strains