Late last week the FDA granted emergency use authorisation for the first Covid-19 antibody test to detect the presence of neutralising antibodies in an individual’s blood. People who have had the coronavirus develop antibodies to it, but not necessarily neutralising antibodies – those capable of blocking cellular infiltration by the virus. Since it detects these antibodies, Genscript Biotech’s cPass Sars-Cov-2 neutralisation antibody detection kit ought to give a better idea than other antibody tests of a person’s chances of being immune to reinfection, though it should be stressed that a link between the presence of any kind of antibodies and immunity has yet to be definitively proven. According to the assay’s instructions for use, a trial comparing it with a plaque reduction neutralisation test – the gold-standard means of detecting neutralising antibodies – yielded 100% positive and 100% negative percent agreement, analogous to sensitivity and specificity respectively. A separate trial published in Nature Biotechnology found it to have 95-100% sensitivity and 99.9% specificity. Tests such as Genscript’s will have a major role to play in tracking patients’ response to Covid-19 vaccines which aim to elicit neutralising antibodies, including the project from Pfizer and Biontech which reported impressive pivotal data today.
Note: "Other" includes seven antigen tests, five home sampling kits, three saliva collection devices and two IL-6 tests.