· Seroprevalence of anti-SARS-CoV-2 antibodies may indicate positive impact from vaccines. A team from the Wuhan Center for Disease Control and Prevention conducted a cross-sectional assessment of the prevalence of anti-SARS-CoV-2 antibodies in a random sample of 9,542 Wuhan residents in April 2020, with two follow ups in June and October-December 2020. They found no significant decrease in IgG or neutralizing antibody titers in the 335 individuals who tested positive at the first appointment. Authors suggest the promise of durable immunity indicates vaccines could help prevent the resurgence of the epidemic in previously exposed populations.
Understanding the Pathology
· Can IgG antibodies be useful for passive immunization? Immunologists and pharmacists from several Chinese institutions used indirect ELISA to analyze IgM and IgG antibody levels in 32 COVID-19 patients from day 1 to day 24 of infection. They found that SARS-CoV-2 specific IgM was measurable for a shorter period (peaking at 20 days post-infection and beginning to fall around day 25), with IgG antibodies persisting throughout the time frame. The authors suggest IgG antibodies represents the primary immune response and propose its use for passive immunization treatment in COVID-19.
· Persistence of SARS-CoV-2 can be monitored through N-Antibody levels. Members of the LondonCOVID Group conducted a prospective SARS-CoV-2 serological study of 1,069 healthcare workers across 4 hospitals in London between March and July 2020. They found 29% (n=312) developed antibodies against nucleocapsid (N) protein (95% CI 26%–32%) which steadily increased and stabilized in the 12 weeks after the first seropositive test (Figure). Because anti-N antibody titers were similar between those with and without COVID-19 symptoms, authors suggest N antibody could be a reliable surveillance indicator for past infection with SARS-CoV-2.
· There is a trend of dropping anti-SARS-CoV-2 plaque reduction neutralization test titers over time in convalescent plasma donors. A team of microbiologists from the Canadian Blood Services in Alberta conducted Plaque Reduction Neutralization Tests (PRNT50) to detect levels of SARS-CoV-2 neutralizing antibodies in plasma products from 30 previously COVID-19 positive male blood donors with repeated donations. In 50% of the donors (n=15) they observed an eightfold drop in PRNT50 titers at 91-143 days from initial infection compared to peak PRNT50. Because SARS-CoV-2 antibodies titers appear to decline from peak values in 3-4 months, authors caution against relying on repeat donors when recruiting convalescent plasma donors.
R&D: Diagnosis & Treatments
· CRISPR-augmented RT-PCR may provide more sensitive tracking of circulating viral RNA of SARS-CoV-2 infection. Experts in molecular diagnosis and infectious disease from Tulane University, among others, evaluated the performance of a CRISPR-augmented RT-PCR for detecting SARS-CoV-2 in plasma samples from experimentally infected nonhuman primates (NHP) as well as 159 patients (adult and pediatric) with negative nasal swab RT-qPCR. Using nasopharyngeal swab RT-PCR as confirmatory tests, they found the assay accurately detected SARS-CoV-2 RNA in the blood of NHPs and humans. The test exhibited a 91.2% sensitivity and 99.2% specificity in the human patient cohort as compared to only 41% sensitivity with non-augmented RT-qPCR. Authors suggest SARS-CoV-2 can be reliably detected in the blood of patients negative nasal swab RT-qPCR and could improve detection of SARS-CoV-2 infection.