Can vaccines be given together?

01 November 2009


Vaccine injection



Can vaccines can be given together? I know someone that just received four vaccines at once. Can they wear out the immune system and not produce as good a response?


Dr Chris Smith answered this question...

Chris - The answer is both yes and no!

When you give vaccines to people, what you're aiming to do is get the immune system to respond so that it can recognise that pathogen in the future and protect you, either with antibodies or cells that kill viruses in cells.

Now, one way of vaccinating people is what's called Live Attenuated Vaccine. This is where you grow viruses in culture for many generations, and, through the effects of mutation, they lose the ability to make you ill, but they nonetheless remain infectious. So, with the MMR - Measles, Mumps and Rubella - for example, you put the virus into the person. It doesn't cause severe disease, but what it does do is to display to the immune system the entire repertoire of viral genes, viral proteins. And what that does is it makes a very broad immune response, involving making both antibodies and cells that can attack virally infected cells. That way, your body is very powerfully primed to recognise and prevent you from getting that virus in the future.

The problem is that, when you go into that state of infection, what it does is to release large amounts of a signalling hormone called interferon - Alpha interferon, in fact. And what that does is put all the cells in the body into this anti-viral state where the cells are undergoing surveillance. They increase the surface markers they display to the immune system so that they're more likely to get killed if they've got a virus in them; they degrade genetic material that they think might be viral; and they become much harder to infect for viruses.

Now, that means if you've had one virus, that's attenuated vaccine, about a week or two before, your body makes loads of this interferon. If you then come along and then try and infect yourself with another attenuated virus, for instance another vaccine, it won't work very well because it doesn't get into the cells, and the body kills it really quick before it has a chance to prime your immune system.

So, live vaccines, if you don't have them at the same time is a bad thing to do. Having them all together is fine because the immune system works by discriminating very powerfully between different epitopes that different viruses display anyway. So that's not a problem.

For the present situation we're in now though, people are asking me, "What about flu vaccines?" Because lots of people had a seasonal flu vaccine but then they're also saying, "Well now, we need to have a swine flu vaccine. Will the fact that I had the seasonal vaccine about two weeks ago make a difference for me having the swine flu vaccine now?" And the answer is not in that circumstance, no, because the flu vaccine is a killed vaccine. You're just putting in bits of dead virus - shrapnel if you like - which the immune system then learns to recognise.

This doesn't trigger the same interferon response, so it doesn't make you feel ghastly in the same way. It doesn't actually prevent you getting infected with other viruses in the same way.

Dave - Is this interferon response the reason why I still feel really quite shattered now, two weeks after I had the flu?

Chris - Yeah and the reason that flu makes you feel so rotten, despite the fact that the virus is only confined to your respiratory tract, nose and throat, and sometimes lungs if you get a very severe infection, you probably had symptoms that were nonetheless across your whole body. Muscle aches and pains, tiredness, very bad headache, temperatures, just feeling ghastly. That's because of these hormones, the interferons, that the body produces in response to the infection, which then turn all of your cells into this very antiviral prime state. So, exactly right, yeah and that's why after some vaccines that do provoke lots of interferons to be released, you have a day of feeling a bit rotten. It's not because you're infected, although you might be. It's actually the interferons - it's your body's own hormones that are making you feel like that.


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