ABSTRACT
We reviewed the diagnostic accuracy of SARS-CoV-2 serological tests. Random-effects models yielded a summary sensitivity of 82% for IgM, and 85% for IgG and total antibodies. For specificity, the pooled estimate were 98% for IgM and 99% for IgG and total antibodies. In populations with ≤ 5% of seroconverted individuals, unless the assays have perfect (i.e. 100%) specificity, the positive predictive value would be ≤ 88%. Serological tests should be used for prevalence surveys only in hard-hit areas.
Subject(s)
Antibodies, Viral/blood , Clinical Laboratory Techniques/methods , Coronaviridae Infections/diagnosis , Coronavirus Infections/diagnosis , Coronavirus/immunology , Pneumonia, Viral/diagnosis , Serologic Tests/standards , Severe Acute Respiratory Syndrome/immunology , Betacoronavirus , COVID-19 , COVID-19 Testing , Clinical Laboratory Techniques/standards , Coronavirus/isolation & purification , Coronavirus Infections/epidemiology , Coronavirus Infections/immunology , Humans , Immunoglobulin G/blood , Immunoglobulin M/blood , Pandemics , Pneumonia, Viral/epidemiology , Pneumonia, Viral/immunology , Predictive Value of Tests , SARS-CoV-2 , Sensitivity and Specificity , Serologic Tests/methods , Severe Acute Respiratory Syndrome/bloodABSTRACT
The correlation between immune responses and protection from SARS-CoV-2 infections and its duration remains unclear. We performed a sanitary surveillance at the European Institute of Oncology (IEO) in Milan over a 17 months period. Pre-vaccination, in 1,493 participants, we scored 266 infections (17.8%) and 8 possible reinfections (3%). Post-vaccination, we identified 30 infections in 2,029 vaccinated individuals (1.5%). We report that the probability of infection post-vaccination is i) significantly lower compared to natural infection, ii) associated with a significantly shorter median duration of infection than that of first infection and reinfection, iii) anticorrelated with circulating antibody levels.
Subject(s)
Antibodies, Anti-Idiotypic/blood , COVID-19 Vaccines/administration & dosage , COVID-19/immunology , Immunoglobulin G/blood , Adult , Aged , Aged, 80 and over , Antibodies, Anti-Idiotypic/immunology , Antibodies, Viral/blood , Antibodies, Viral/immunology , COVID-19/blood , COVID-19/prevention & control , COVID-19/virology , Female , Humans , Immunoglobulin G/immunology , Male , Mass Vaccination , Middle Aged , SARS-CoV-2/immunology , SARS-CoV-2/pathogenicity , Time Factors , Young AdultABSTRACT
Although antibody response to SARS-CoV-2 can be detected early during the infection, several outstanding questions remain to be addressed regarding the magnitude and persistence of antibody titer against different viral proteins and their correlation with the strength of the immune response. An ELISA assay has been developed by expressing and purifying the recombinant SARS-CoV-2 Spike Receptor Binding Domain (RBD), Soluble Ectodomain (Spike), and full length Nucleocapsid protein (N). Sera from healthcare workers affected by non-severe COVID-19 were longitudinally collected over four weeks, and compared to sera from patients hospitalized in Intensive Care Units (ICU) and SARS-CoV-2-negative subjects for the presence of IgM, IgG and IgA antibodies as well as soluble pro-inflammatory mediators in the sera. Non-hospitalized subjects showed lower antibody titers and blood pro-inflammatory cytokine profiles as compared to patients in Intensive Care Units (ICU), irrespective of the antibodies tested. Noteworthy, in non-severe COVID-19 infections, antibody titers against RBD and Spike, but not against the N protein, as well as pro-inflammatory cytokines decreased within a month after viral clearance. Thus, rapid decline in antibody titers and in pro-inflammatory cytokines may be a common feature of non-severe SARS-CoV-2 infection, suggesting that antibody-mediated protection against re-infection with SARS-CoV-2 is of short duration. These results suggest caution in using serological testing to estimate the prevalence of SARS-CoV-2 infection in the general population.