LS: Speaking of Science Column October 06, 2008

Flu virus mutates every year, so the vaccine changes

Each fall, the push starts to vaccinate all high-risk people against influenza. Influenza is a virus that causes severe cough, fever, sore throat and muscle pain.

It is deadly, killing 250,000 to 500,000 people a year worldwide. Despite these alarming numbers, the vaccine prevents disease in 70 percent to 90 percent of healthy adults.

But why do we need to be vaccinated every year? Why are there shortages of vaccine some years?

Why do they say some years the vaccine isn’t as effective as others?

Influenza and the production of the influenza vaccine every year is an amazing process.

First of all: What are immunizations and how do they work? This is a long story, but to put it simply, when our body is exposed to bacteria, viruses and other foreign materials, it recognizes them as foreign and produces specific antibodies. Antibodies are proteins that attach to the alien protein on one end and to a white blood cell or other immune cell on the other.

Once recognized, the body quickly disposes of the infectious agent.

The next time that intruder comes around, the body remembers it and the antibody response is rapid enough to prevent infection. An immunization is an efficient way to use the body’s natural defenses to prevent illness.

The challenge with the influenza virus is that it changes or mutates every year. This is called “antigenic drift.” This “drift” makes vaccine production challenging because every year the virus changes just enough so that the body cannot recognize it. Influenza vaccine development is a year-round process.

The development of an effective vaccine starts in February in the Northern Hemisphere.

In the middle of the “flu season,” members of the World Health Organization’s Global Influenza Surveillance Network are busy tracking that year’s infection. There are two main types of Influenza, A and B, and many subtypes.

Tests are done during the influenza outbreak to determine the most common or worse subtypes within the main types. Representatives from the 94 countries in the network then meet to decide which three flu subtypes will be the most virulent.

Last year, they had 10,000 active subtypes to choose from. When the subtypes in the vaccine don’t completely match those causing illness during flu season, there is a “mismatch.” Even in “mismatch” years, the vaccine provides partial protection, and in one of those years, 2003–2004, the vaccine still prevented 90 percent of flu hospitalizations.

Production begins. The vaccine is developed over the spring using chicken eggs. The shell of a 10-day-old egg is cracked, and flu virus is injected into the fluid that surrounds the chick embryo. The egg is then resealed, and two days later the virus is harvested and purified.

The virus is broken up, and only the proteins necessary to stimulate the body to produce antibodies are put into the vaccine.

During the summer, the virus is tested and made ready for distribution in August. The timing of the process is opposite in the Southern Hemisphere, where the seasons are opposite of ours.

Any problems during this six-month process will result in a shortage of vaccine. The shot-distributed immunization does not contain whole virus, so you can’t “get the flu” from the vaccine, but your arm may ache for a few days. There is a nasal spray vaccine that has live virus in it, but the virus is very weak, so that it can’t cause infection.

What is in store for the future? Right now research is being conducted on a universal influenza vaccine. This vaccine will be to a different protein, the M2 protein, which has not changed much in the last hundred years.

The viruses can be grown in large vats, obviating the need for the chick eggs, and the antibody response may be good for many years. The vaccine also can be stockpiled and released on short notice.

The best news about the vaccine is that is prevents bird flu also. We will still need to get two to three annual shots initially, but then it will be a shot every five to 10 years.

That vaccine is still a few years off but holds promise for a universal vaccine that will nearly eliminate the need for such a large distribution of shots that exists now.

With resistance among bacteria and viruses developing faster than new medicines to treat them, immunizations are our key to preventing diseases, further protecting against disease and death in our daily lives.


Dr. Barbara Zind is a pediatrician with Western Colorado Pediatrics and a volunteer at the Math & Science Center. Dan Preston is a senior at Fruita Monument High School.


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