(This post is part of a series of guest writings by Dr. Mark McColl answering reader questions. Please read my vaccine history and Dr. McColl’s introduction before continuing.)
What’s the deal with the flu shot- who actually needs it, how effective is it?
The flu shot effectiveness is variable depending on several different factors not the least of which is the patient’s immune system. Some people genetically lack certain factors of their immune system that inhibit the body’s ability to develop appropriate protection. Age plays a big factor also. The elderly respond dramatically less well than similarly healthy younger adults. Other factors include things like dose, prior exposures or vaccinations, and timing of vaccination relative to the exposure.
Influenza as a virus mutates very quickly. Within a season it can mutate either a small amount or a large amount. This rearranging of the genetic material can occur with other strains of influenza that generally infect other animals. Given these continual changes the flu vaccine has to be reformulated with the predicted dominant strains each season. Sometimes the strains that pass through your community are the ones that were in the vaccine. In fact, lots of the time this is the case. Protection in this scenario is very good. You may have somewhere around an 80% chance (again, my professional opinion and not a documented study) of not acquiring the infection were you to be exposed. I will say that I’ve never had a patient who had been vaccinated die from an influenza infection. I can’t say that about those that were unvaccinated. In the end, I’m much more interested in stopping preventable causes of death than stopping non-fatal respiratory tract infections.
As to who needs it, I think everyone does. If your community were to vaccinate about 80% of the people against influenza there would probably be no influenza related deaths. Right now more people in your town die from influenza than die in car accidents.
One thing to mention about influenza is the recent concern for ‘bird flu’ and the recent epidemic of ‘swine flu’. The reason these are so problematic has to do with the different genes that can be rearranged in these viruses. In an oversimplified fashion, influenza has a gene that controls how infective it is and a gene that regulates how fatal it is. The ‘swine flu’ strain had a very powerful version of the infective gene but the fatal gene was relatively weak. About 90-95% of people exposed to the ‘swine flu’ were infected. It was fatal, but not nearly as fatal as the ‘bird flu.’ Avian influenza, or the ‘bird flu’, has a mortality rate of about 99%. Meaning that almost 100% of people who acquire the infection die. It’s infective gene is thankfully weak and in requires a pretty large exposure of the bird’s blood or secretions to be infective. Bird handlers and butchers who tend to be exposed to the blood and inhale small particles of blood seem to be the ones most infected.
Now, the important tidbit to this story is the fact that most influenza strains can infect more than one species of animal and more than one strain can infect the same animal at one time. That’s a lot of how the virus mutates so quickly every year. Imagine some poor unsuspecting pig who comes down with ‘swine flu’. His owner decided he needed a good companion so he introduced a large group of chickens. One of these chickens has ‘bird flu’ and transmits that to the pig. Now inside the pig these viral strains are rearranging. Many mutations are less effective at survival and die off but some are stronger. The farmer comes along with his own case of ‘human flu’ and infects the pig population by sneezing all of over them. This doomed pig now has three influenza viruses running amok inside. As he is handled by the farmer’s son during the daily chores he transmits a new strain of ‘bird-swine-human flu’ to the boy. This poor boy is contagious and spreading the disease for several days at school before the first fever. His infection has the infective gene of the ‘swine flu’ (90% of the people exposed get it) and the fatality gene of the ‘bird flu’ (ie, 99% of infected people die from it). What kind of world epidemic will come from this? How many in his school and community will die from it? The international health community is waiting for just such an event to occur. It isn’t an issue of ‘if’ but ‘when’.
Is it true that the flu vaccine has been linked to guillain-barre syndrome?
Yes but rarely. Do you know where rheumatic heart disease comes from? The bacteria that causes strep throat (group A streptococcus) is covered with different foreign proteins. Many of which can be a good source for the body to identify and develop antibodies toward. When these antibodies are released into the blood stream they go looking for the proteins they were designed to destroy. They don’t intuitively know that the tonsils are the most likely location. They have been instructed to search everywhere from the toes to the nose. One of these bacterial proteins looks an awful lot like a protein found on the mitral valve of the human heart. Sometimes they look so much like each other that the antibodies designed to destroy foreign invaders mistakes the mitral valve as the enemy and attacks it. If strep throat is treated with antibiotics within nine days of onset of symptoms this is prevented.
When a person is vaccinated the body takes those proteins and begins to develop antibodies toward them. That way if the person is exposed to the actual infection and those proteins are seen again, it will be prepared. The response and clearance time are much quicker and, in general, will save the person’s life. If one of these antibodies finds a similar looking protein on a nerve it can damage the nerve and cause all manner of problems including potentially Guillian-Barre’ syndrome. Incidentally, a common bacterial gastrointestinal infection called Campylobacteri jejuni causes a similar cross reaction of antibodies and nerve damage to cause Guillian-Barre’ syndrome.
The association with Guillian-Barre’ and influenza vaccination occurred in 1976 where that season’s strain increased the risk of Guillian-Barre’ to 1 per 100,000 people receiving the vaccine. Since then there has been no association with Guillian-Barre’ and influenza vaccination.
At what point does the risk of the vaccine outweigh the risk of the disease?
The risk of the vaccines outweigh the risk of the disease rarely. A few examples would be in patients who have had a prior serious reaction to a particular vaccine. Those with allergies to components of the vaccine. Those with known seriously weakened immune systems such as particular immunodeficiencies or systemic steroid/chemotherapy use may need to exclude certain vaccines. Some vaccines haven’t been well studied in pregnancy so should be avoided until certain trimesters or until after delivery.
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