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The South African serology results from the @Novavax vaccine trial drastically need more clarification. From the protocol posted in their Phase 2 results it appears they used an in-house ELISA for anti-spike IgG ( https://www.nejm.org/doi/suppl/10.1056/NEJMoa2026920/suppl_file/nejmoa2026920_appendix.pdf). There are several issues with this 1/
Number one being is that I can't find any information on the sensitivity and more importantly the specificity of the assay they used. This is critically important info because A) they report an extremely high rate of seropositivity in their trial (30%) and 2/
B) they claim that seropositivity had no protective effect against the B.1.351 or South African strain. These claims are problematic for several reasons 3/
Reason 1) There is good evidence from several studies of serology tests over a variety of diseases (HIV, Herpes etc) that some (but not all) serology tests are significantly less reliable when testing African samples 4/
Reason 2) The rate of seropositivty they report is pretty high when compared to other areas of the world that have also experienced high rates of infection. The rates may be true but without the Sens and Spec data it's impossible to know what's real and what's assay error 5/
Reason 3) They find no boosting of protection in the vaccine arm of the "seropositive" people. This is really strange since the preliminary data from other seropositive-vaccine boost studies show a Massive increase in immune response after the first dose, but here nothing 6/
This could be due to the SA variant as they claim but all the data from other sources around the world that have looked at the variant in vitro would suggest that even if some of the Neutralizing antibody response is lost there should still be protection in some 7/
Also if previous infection had 0 protective effect against the new variant, we should be seeing WAY more reinfections that we are, especially in South Africa 8/
Taken together I think we should treat the claims by the Novavax research team that previous infection is not protective against variant B.1.351 as highly speculative, if not flat out wrong, until their ELISA results are more rigorously examined. 9/9
