“It seems that by default they only give you the core,” Mr. Lat said. “I never thought of asking for another one. “
In May, the Food and Drug Administration recommended against using antibody tests to assess immunity – a move that has criticism attracted from some scientists – and provided only rudimentary information on testing to healthcare providers. Many doctors are still unaware of the differences between antibody tests or the fact that the tests only measure one form of immunity to the virus.
Rapid tests that are commonly available give a yes-no result and may lack low levels of antibodies. A certain type of lab test, called an Elisa test, can offer a semi-quantitative estimate of antibodies to the spike protein.
It is also important to wait to be tested at least two weeks after the second injection of Pfizer-BioNTech or Moderna vaccines, when antibody levels have increased enough to be detectable. For some people receiving the Johnson and Johnson vaccine, this period can be up to four weeks.
“This is the timing, the antigen and the sensitivity of the test – these are going to be very important,” Dr Iwasaki said.
In November, the World Health Organization set standards for antibody testing, allowing comparison of different tests. “There are a lot of good tests out there now,” Dr. Krammer said. “Little by little, all these manufacturers, all these places that operate them are adapting to international units.
Antibodies are only one aspect of immunity, noted Dr. Dorry Segev, transplant surgeon and researcher at Johns Hopkins University: “There’s a lot going on below the surface that antibody tests don’t measure. not directly. The body also maintains what’s called cellular immunity, a complex network of defenders that also respond to invaders.