Sometimes, people ask about whether it would be better to get a blood test to see if a vaccine is necessary. The thought being that by getting one’s blood tested, a person may not need to get as many doses of a vaccine.
But this idea is not as straightforward as it may seem:
- Blood tests require getting a needle. So, for those who resist vaccines because of needle-phobia, this approach could actually increase the number of needles a person needs to get.
- No test is perfect. So, some people might appear to be immune when they are not and vice versa.
- The majority of the time, an extra dose of vaccine is not harmful. If a person is immune, the extra dose of vaccine will strengthen existing immunity. Likewise, in most cases, if a person’s immune system has previously “seen” the potential pathogen, either through natural infection or vaccination, they are less likely to experience untoward events following vaccination.
- Blood tests cost money (often as much money as the vaccine). For these reasons, testing large numbers of people, some of whom will still need to be vaccinated, does not make a lot of sense.
In this video, Dr. Paul Offit discusses some of the considerations and limitations related to the idea of antibody testing prior to vaccination.
Paul Offit, MD: Hi, my name is Paul Offit. I’m talking to you today from the Vaccine Education Center here at Children’s Hospital of Philadelphia. One thing that parents worry about, or wonder about is, do I really need a vaccine if I’ve already had one or two doses? Do I really need to finish out the schedule, for example? Or maybe I’ve already been exposed to a virus or bacteria, so I don’t’ really need to even get vaccines at all.
So instead, how about if I just have my blood tested to see whether or not I have a protective immune response already against that particular virus or bacteria.
It’s not as easily done as you would think. So, for example, for some pathogens like the bacterium Haemophilus influenzae type B or the virus hepatitis B, if you have a certain quantity of antibodies in your blood, you can virtually be guaranteed that you will not get that disease if you’re exposed to that bacteria or virus. For those two it’s clear.
For some, it’s less clear. So, for example, if you have antibodies directed against measles virus that are of a certain titer, you be can pretty much assured that you are not going to get measles then if you are exposed to the natural or wild type virus. However, there was an outbreak of measles in the late 1980s, early 1990s that swept through the United States that caused more than 50,000 hospitalizations and caused about 120, children mostly, to die from measles.
When people looked back at that outbreak, you found that there were many people who had been vaccinated, but who didn’t have antibodies against measles who were still protected. The reason they were still protected is they had something called memory cells. Memory immunological cells, like B- and T-cells, which then when they were exposed to the virus became activated, differentiated, made antibodies, which then protected them. So even though they didn’t have circulating antibodies in their bloodstream, they still have these memory cells in their immune system that could then respond when they were exposed. So, if you looked at those people and saw they didn’t have antibodies, you would have falsely concluded they weren’t protected when they were.
Sometimes you can have antibodies in your bloodstream and not be protected. So, for example rotavirus or pertussis bacteria affect really just the mucosal surfaces. So, rotaviruses just infect the lining of the small intestine. Pertussis or whooping cough infects sort of the lining of the trachea or windpipe and the lungs. That virus and that bacteria don’t really spread into the bloodstream and cause a systemic infection. They’re so-cause mucosal infections. So when you look at immunity in the bloodstream, that doesn’t necessarily predict whether or not there’s going to be adequate immunity at that mucosal surface.
The point being that titers are difficult. They’re not a cure-all. They’re not a perfect predictor. So, I think that the best way of knowing that you’re protected is to get the vaccines that are recommended at the time they are recommended. Thank you.
Related Centers and Programs: Vaccine Education Center