World Health Organization Scientific Brief regarding Immunity Passports for Covid-19 April 24, 2020.

World Health Organization Scientific Brief regarding “ Immunity Passports” for Covid-19 April 24, 2020. The WHO has stepped into the controversy  regarding the usefulness of individual serologic tests for Covid-19.   This Scientific Brief appears to be prompted by recent efforts to expand   immunologic testing on the population, and utilize such test results to determine who is immune.  The WHO strongly disagrees with that approach.

In the Brief, a simple but helpful discussion of immune response is outlined.  The body initially responds to a viral assault with a non-specific innate immune reaction which leads to recruitment of macrophages, neutrophils, and dendritic cells.  Next a more specific adaptive response leads to the development of antibodies to the virus, and the production of T cells which eliminate other infected cells in the body.   Studies of people who have recovered from Covid-19 show that most have measurable antibodies, but in some, the levels of neutralizing antibodies are  low, suggesting that the T-cell response, rather than the level of antibodies, may be more important in developing immunity.  Thus far, there are no studies that have documented that SARS-2 Covid antibodies confer immunity to subsequent infection.

There is also concern that significant variabilty exists among the various immunologic diagnostic tests currently being utilized.  Inaccuracies  in immunodiagnostic tests can  result in several bad outcomes.  False negative tests can give individuals a false sense that they have not been infected; on the other hand,  false positive tests may give people the impression that they have antibodies when they do not.  They might stop wearing masks, assuming they are no longer at risk.  Some tests may incorrectly register antibody to other “common cold” Corona virueses.  As already discussed, even if people have antibodies to Covid-19, , there is at present no convincing evidence that these antibodies provide protection from future infections.

Commentary: Sheila Fallon-Friedlander
This publication reminds us that it is premature to rely on antibody testing to determine who will be absolutely immune from future infection.  However, population studies remain very important in defining the overall prevalence of disease in any given area, and better defining possible high-risk groups.  Such information will also be useful in determing when and how to carry out relaxation of isolation policies.