CD40LG and COVID-19: The combined specificity of LFAs with pre-pandemic samples was 81.3% for U.S. pre-COVID-19 samples, but only 68.2% for sub-Saharan pre-COVID-19 samples (P = 0.053), but this difference was mostly a result of lower IgM specificity (82.5% versus 68.2%, P = 0.032).