One of the major arguments against vaccine-induced immunity is that it primarily stimulates the humoral immune system and not the cellular immune system. Antibodies are produced by the humoral immune system and then routinely measured to determine ‘immunity.
The problem with this approach is that you can have high antibody levels and still get the disease. It’s very difficult and expensive to measure the cellular immune response, and immunologists admit that they are still in the dark about a lot of the finer points of the overall immune response.
When you use antibody titers or blood levels to check for immunity, all you’re doing is getting a picture of what happened (you had an immune response); it doesn’t tell you whether you’re going to be immune in the future, because antibodies are only one aspect of the immune response, and in some cases are not even necessary to easily combat the sickness and become immune.
Traditionally, the way immunity is determined is to do a test that measures antibodies, which is the humoral immune system. But there’s no good way to assess the cellular immune system. It’s a really imprecise science at best
— Joseph Mercola, DO
Mercola J. The Forgotten History of Vaccinations You Need to Be Aware Of. Mercola.com Jan. 18, 2015.