How does the flu vaccine work, since viruses can't be "killed"?

2601>Growing up I was always taught that it would never be possible for scientists to come up with a flu vaccine because flu is caused by a virus, which is not a living thing. Because of that, they would not be able to "kill" it and put it in a vaccine that would trigger the immune response without making you sick. So how do the flu vaccines work and are they really effective?
Reply:It is a bit debatable whether viruses are alive or not. They are not capable of independent existence, but they do have similar components, ( DNA or RNA), to living organisms.





There are basically two types of vaccine, live attenuated vaccines and 'killed' vaccines. The live vaccines are a weaker strain of the disease virus that share surface antigens and so stimulate the immune system without causing disease. A 'killed' vaccine is a virus that has been denatured so that it can no longer cause disease but still has the antigens necessary to stimulate the immune response. Basically you can damage the DNA without destroying to coat antigens needed for a vaccine.





I believe the main problem with the flu vaccine is the ability of the flu virus to mutate it's surface antigens and therefore escape detection by an immune system primed to respond to different antigens.





I just checked, both 'live' and 'killed' flu vaccines are available.
Reply:First of all, yes, the flu vaccine really works. But what does this mean? It means that someone who takes the vaccine is LESS LIKELY to get sick during flu season than someone who does not take the vaccine. It's not 100% effective.





You have to remember, now, that we are talking POPULATION averages. There are always INDIVIDUALS that get sick from the flu that have taken the vaccine. This does NOT mean that the vaccine is ineffective. It just means that some people can naturally resist the flu better than others, with or without the shot. If you measured EVERYONE who gets the vaccine versus EVERYONE who does not, you will see a difference, it "works". That is why we spend millions of dollars each year on improving the vaccine each year with the latest strains.





So how does it work? You are right in saying that technically a virus is not "alive" (although Lysol claims to "kill" certain viruses--check the label). A virus DOES reproduce, but it CANNOT do this on its own. A virus is a simple protein capsule with some amino acids in it. To reproduce, it must invade living cells and take over a cell's function.





OK, now here comes the part I'm not sure of. The body fights off illness with white blood cells. For certain diseases, once you get better, the body can "recognize" a bacteria, and immunity is built up, which is why you can only get chickenpox once. Perhaps the flu vaccine introduces a small amount of flu viruses into the body, hoping to trigger a "recognition" response. Now, if the white blood cells can prevent them from ENTERING THE CELLS, the virus cannot reproduce. If the white blood cells can either bond with or disable the virus, they can be excreted from the body without the virus causing harm.





You can see that I'm not a biologist, but it would probably go something like that.
Reply:Regardless if they are live or killed vaccines, the flu vaccine 'primes' your immune system by giving the immune system a 'look' at what the flu kind of looks like, and the adaptive immune system builds up antibodies, so if you happen to get hit with the flu, it can neutralize the virus. The vaccines are highly weakened, so it is easy for the immune system to handle. They call this 'attenuation'.





They are effective if the current circulating flu is the same as the vaccine or very close to it. If not, then you can get the flu, but if you're lucky, you'll get a milder form.





For what its worth, if you did get the flu within the last 10-years, and there has not been a major change is the type of flu circulating, you are fairly well protected already. Current studies say that you can get protection from 8-10years.
Reply:You need to be retaught. Inactivated influenza virus when injected stimulates a TH2 humoral response which produced antibody. Antibody knocks out all live virus when it emerges from the cells. There is also some TH1 which can kill the infected cells also. There are many flu vaccines and all are somewhat effective but only for a specific strain and only for a certain duration of time.