Longitudinal analysis of clinical serology assay performance and neutralising antibody levels in COVID19 convalescents

Abstract

Objectives:To investigate longitudinal trajectory of SARS-CoV-2 neutralising antibodies and the performance of serological assays in diagnosing prior infection and predicting serum neutralisation titres with time Design Retrospective longitudinal analysis of a COVID19 case cohort . Setting NHS outpatient clinics Participants Individuals with RT-PCR diagnosed SARS-CoV-2 infection that did not require hospitalization Main outcome measures The sensitivity with which prior infection was detected and quantitative antibody titres were assessed using four SARS-CoV-2 serologic assay platforms. Two platforms employed SARS-CoV-2 spike (S) based antigens and two employed nucleocapsid (N) based antigens. Serum neutralising antibody titres were measured using a validated pseudotyped virus SARS-CoV-2 neutralisation assay. The ability of the serological assays to predict neutralisation titres at various times after PCR diagnosis was assessed. Results The three of the four serological assays had sensitivities of 95 to100% at 21-40 days post PCR-diagnosis, while a fourth assay had a lower sensitivity of 85%. The relative sensitivities of the assays changed with time and the sensitivity of one assay that had an initial sensitivity of >95% declined to 85% at 61-80 post PCR diagnosis, and to 71% at 81-100 days post diagnosis. Median antibody titres decreased in one serologic assay but were maintained over the observation period in other assays. The trajectories of median antibody titres measured in serologic assays over this time period were not dependent on whether the SARS-CoV-2 N or S proteins were used as antigen source. A broad range of SARS-CoV-2 neutralising titres were evident in individual sera, that decreased over time in the majority of participants; the median neutralisation titre in the cohort decreased by 45% over 4 weeks. Each of the serological assays gave quantitative measurements of antibody titres that correlated with SARS-CoV-2 neutralisation titres, but, the S-based serological assay measurements better predicted serum neutralisation potency. The strength of correlation between serologic assay results and neutralisation titres deteriorated with time and decreases in neutralisation titres in individual participants were not well predicted by changes in antibody titres measured using serologic assays. Conclusions: SARS-CoV-2 serologic assays differed in their comparative diagnostic performance over time. Different assays are more or less well suited for surveillance of populations for prior infection versus prediction of serum neutralisation potency. Continued monitoring of declining neutralisation titres during extended follow up should facilitate the establishment of appropriate serologic correlates of protection against SARS-CoV-2 reinfection.

Longitudinal observation and decline of neutralizing antibody responses in the three months following SARS-CoV-2 infection in humans

“…The magnitude of the following decline in neutralizing antibody titres reported here is similar to that observed in several newly reported pre-prints 12,13,20,31,[34][35][36][37][38][39] . In these studies, similar to our observations, those who generated a high neutralizing antibody titre still had high neutralizing antibody titres regardless of the initial decline 12,13,31,35,39 and, for those with lower disease severity, two studies reported 7/34 (ref. 12 ) and 5/80 (ref.…”

“…this is subsequently followed by a decline in virus-specific antibodies as these cells die. We observed a wide range of peak neutralizing antibody titres (98-32,000), similar to other cross-sectional cohorts 21,4,31 , and disease severity was associated with higher neutralizing antibody titres. It is not clear yet why neutralizing antibody responses correlate with disease severity 32 .…”

“…12 ) and 5/80 (ref. 31 ) individuals with a decline to undetectable neutralizing antibodies (ID 50 < 20 or ID 50 < 50, respectively) at the last timepoint studied. In contrast, several studies report a sustained antibody response in the first 3 months after SARS-CoV-2 infection, but these studies report changes in binding antibodies only 34,37,38 .…”

Seroprevalence of Antibodies to SARS-CoV-2 in US Blood Donors

“…Other assays in which antibody reactivity wanes over time are less suited to detect previously-infected individuals but tend to correlate more closely with neutralizing antibody titer. 18 In our study, higher S/C values for spike Total Ig were associated with male sex, non-Hispanic Native American/Alaskan and Black race/ethnicity, and Hispanic ethnicity. Whether this correlates with the severity of infection or indicates a more vigorous immunologic response remains to be determined.…”

COVID-19 herd immunity in the Brazilian Amazon

“…Assuming all 133 samples were true positives the sensitivity of the Abbott N IgG assay was 77.4% (95%CI 69.6% to 83.7%) on asymptomatic blood donor serosurveillance samples. The Roche assay detects total Ig and the signal is more stable than the Abbott assay 22 . As samples in July were donated four months into the on-going epidemic in São Paulo, the false negatives on the Abbott assay include both cases that did not initially seroconvert ("serosilent" infections), as well as remote infections with subsequent seroreversion.…”