Feature Article: A Blood Test or a Vaccine?

Sometimes, people contact us to 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.

Recently, some people have even proposed creating laws that would require the opportunity for titer testing before receipt of a vaccine. For example, such a bill has been proposed in Arizona in 2019.

But this idea is not as straightforward as it may seem:

1. Blood tests require getting a needle; so for those who resist vaccines because of needle-phobia, this approach could actually increase the number of shots a person needs to get.
2. No test is perfect, so some people might appear to be immune when they are not and vice versa.
3. 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.
4. 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.

“Can a Blood Test Replace a Vaccine Dose?” is a new video in the Science Made Easy series in which Dr. Offit discusses some of the considerations and limitations related to testing blood for antibodies against vaccine-preventable diseases.