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Name: Morgan
Status: student
Grade: 9-12
Location: WA
Country: USA
Date: Fall 2013

Question: How do scientists know how to make a flu vaccine if viruses can be different every year?

Hi Morgan,

Thanks for the question. For North America, usually the flu season is in winter. However, when it is summer in North America, it is winter in South America. By isolating and studying the flu viruses that are present in South America during their winter, scientists can determine which flu strains require vaccine development. So, flu vaccines are made from data collected during the winter in South America.

I hope this helps. Please let me know if you have more questions. Thanks Jeff

It's a very complicated process. Viruses usually begin in Asia and travel west around the world over the year. Scientists monitor and share information as to which viruses seem to be the most prevalent from year to year. Even though there may be many different strains, they must pick the 3 that appear to be the ones that will make the most people sick. They have about 9 months to predict and choose which strains will be put into the coming year's vaccine. Last year they were very happy with the ones they chose and said there was "good match" between the strains that were circulating in the US and the ones they predicted, yet the match was about 60%. This means that even if you got the vaccine, you could still get influenza if you caught one of the strains that wasn't in the vaccine.

Hope that answers your question.



The attached pdf file from this URL explains pretty clearly the process for developing flu vaccines.

Sincere regards, Mike Stewart

Basically, its all educated guesswork. Scientists consider three candidate viruses that are most likely to be problematic during the flu season and develop a vaccine cocktail (trivalent vaccine) that confers protection to all three. Admittedly, the tendency of the influenza virus to mutate makes it difficult to stay one step ahead.

Dr. Tim Durham Assistant Professor of Agronomy and Agricultural Science Ferrum College


This is an excellent question. As you know, the influenza virus comes in many different strains and thus a vaccine must be tailored for the strain that you are likely to catch in a given year.

To figure out which flu strains are most likely to be spread throughout the world each flu season, the World Health Organization, in conjunction with national organizations like the Center for Disease Control and Prevention, conduct detailed studies on flu virus trends and release recommendations, normally around February, of the strains that should be vaccinated against for the next flu season. The reason they release these recommendations so early (flu season doesn't start until the following autumn) is because making the large number of vaccines necessary takes quite a bit of time.

As you can imagine, it's hard to guess - even with a lot of sophisticated science - which flu viruses will be prevalent half a year in the future. Sometimes the guesses are better than other times. To help avoid making a lot of vaccine with little benefit, most flu vaccines are actually a combination of several vaccines against different flu strains, all of which are likely to be common strains in the year's flu season. Additionally, research by the CDC has indicated that even if the flu vaccine is not raised against the specific strain that become common, it can still provide some immune protection if the strains are closely related. Thus, even if the WHO recommendations aren't perfect, getting vaccinated will still provide you with some protection against the flu.

S. Unterman Ph.D.

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