Induction of SARS-CoV-2 neutralizing antibodies by CoronaVac and BNT162b2 vaccines in naïve and previously infected individuals

Abstract

Background: A major challenge of the SARS-CoV-2 pandemic is to better define "protective thresholds" to guide the global response. We aimed to characterize the longitudinal dynamics of the antibody responses in naturally infected individuals in Chile and compared them to humoral responses induced after immunization with CoronaVac-based on an inactivated whole virus -or the BNT162b2- based on mRNA-vaccines. We also contrasted them with the respective effectiveness and efficacy data available for both vaccines.

Methods: We determined and compared the longitudinal neutralizing (nAb) and anti-nucleocapsid (anti-N) antibody responses of 74 COVID-19 individuals (37 outpatient and 37 hospitalized) during the acute disease and convalescence. We also assessed the antibody boosting of 36 of these individuals who were immunized after convalescence with either the CoronaVac (n = 30) or the BNT162b2 (n = 6) vaccines. Antibody titres were also measured for 50 naïve individuals immunized with two doses of CoronaVac (n = 35) or BNT162b2 (n = 15) vaccines. The neutralizing level after vaccination was compared to those of convalescent individuals and the predicted efficacy was estimated.

Findings: SARS-CoV-2 infection induced robust nAb and anti-N antibody responses lasting >9 months, but showing a rapid nAb decay. After convalescence, nAb titres were significantly boosted by vaccination with CoronaVac or BNT162b2. In naïve individuals, the calculated mean titre induced by two doses of CoronaVac or BNT162b2 was 0·2 times and 5.2 times, respectively, that of convalescent individuals, which has been proposed as threshold of protection. CoronaVac induced no or only modest anti-N antibody responses. Using two proposed logistic models, the predicted efficacy of BNT162b2 was estimated at 97%, in close agreement with phase 3 efficacy studies, while for CoronaVac it was ∼50% corresponding to the lowest range of clinical trials and below the real-life data from Chile (from February 2 through May 1, 2021 during the predominant circulation of the Gamma variant), where the estimated vaccine effectiveness to prevent COVID-19 was 62·8-64·6%.

Interpretation: The decay of nAbs titres in previously infected individuals over time indicates that vaccination is needed to boost humoral memory responses. Immunization of naïve individuals with two doses of CoronaVac induced nAbs titres that were significantly lower to that of convalescent patients, and similar to vaccination with one dose of BTN162b2. The real life effectiveness for CoronaVac in Chile was higher than estimated; indicating that lower titres and additional cellular immune responses induced by CoronaVac might afford protection in a highly immunized population. Nevertheless, the lower nAb titre induced by two doses of CoronaVac as compared to the BTN162b2 vaccine in naïve individuals, highlights the need of booster immunizations over time to maintain protective levels of antibody, particularly with the emergence of new SARS-CoV-2 variants.

Funding: FONDECYT 1161971, 1212023, 1181799, FONDECYT Postdoctorado 3190706 and 3190648, ANID Becas/Doctorado Nacional 21212258, PIA ACT 1408, CONICYT REDES180170, Centro Ciencia & Vida, FB210008, Financiamiento Basal para Centros Científicos y Tecnológicos de Excelencia grants from the Agencia Nacional de Investigación y Desarrollo (ANID) of Chile; NIH-NIAD grants U19AI135972, R01AI132633 and contracts HHSN272201400008C and 75N93019C00051; the JPB Foundation, the Open Philanthropy Project grant 2020-215611 (5384); and by anonymous donors. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Keywords: COVID-19; Neutralizing antibody persistence; SARS-CoV-2 vaccines; Serological response; Vaccination boost.

Figure 1

Longitudinal dynamics of neutralizing and anti-N antibody responses to SARS-CoV-2 infection from outpatient and hospitalized individuals. a,b. The half-maximum inhibitory concentration (IC50) of sera was determined by microneutralization assay of recombinant vesicular stomatitis virus carrying SARS-CoV-2 spike protein (rVSV-SARS2-S). a. Neutralizing antibody (nAb) titres (log10 IC50) from n = 30 outpatients (116 samples; grey circles) and n = 35 hospitalized (112 samples; red circles) at 2 to 37 days post-symptom onset. c. Longitudinal nAb titres (log10 IC50) from n = 36 outpatients (85 samples) and n = 31 hospitalized (58 samples) taken from day 23 (outpatients) or day 25 (hospitalized) until day 414 post-symptom onset. c,d. The end-point titres of anti-N IgG were determined by ELISA using a recombinant SARS-CoV-2 nucleocapsid protein. Samples and time points are the same as those in A and B. a-c. The second order polynomial (quadratic) curve fitting was used to establish the days at which peak titres occurred (Ymax). b–d. Continuous decay fit is shown with the red and gray line for the corresponding patient group. Every data point represents results from two technical replicates.

Figure 2

Comparison of neutralizing and anti-N antibody responses after SARS-CoV-2 infection of outpatient and hospitalized individuals over a 12 months period. a. nAb IC50 titres were determined by microneutralization assay of recombinant vesicular stomatitis virus carrying SARS-CoV-2 spike protein (rVSV-SARS2-S). b. End-point titres of anti-N IgG were determined by ELISA using a recombinant SARS-CoV-2 nucleocapsid protein. a-b. Samples were obtained for n = 37 outpatients (172 samples; grey circles) and n = 37 hospitalized (139 samples; red circles) grouped by weeks (W) or months (M) post-symptom onset (serum samples from: 1W = 1–7 days; 2W = 8–14 days; 3W = 15–21 days; 4W = 22–45 days; 3M = 46–135 days; 6M = 136–225 days; 9M = 226–315 days and 12-14M = 316–414 days). The bars indicate geometric mean titres (GMT) with 95% confidence intervals. GMTs are indicated above each data set. Dashed line represents the limit of detection (LOD) of each assay. Statistical analyses shown at the indicated time points were performed between nAb titres of outpatient and hospitalized using the unpaired two-tailed Mann-Whitney test (*P < 0·05; **P < 0·01; **P < 0·001; ****P < 0·0001; ns, non-significant). Every data point represents results from two technical replicates.

Figure 3

Longitudinal neutralizing and anti-N antibody titres to SARS-CoV-2 in previously infected before and after CoronaVac or BNT162b2 vaccination. nAb titres (IC50) obtained using a rVSV-SARS2-S microneutralization assay and end-point titres of anti-N IgG were determined by ELISA using a recombinant SARS-CoV-2 nucleocapsid protein for vaccinated previously infected outpatients (a-b; 20 participants) or vaccinated hospitalized patients (c-d; 16 participants) at different time points grouped by weeks (W) or months (M) post-symptom onset (serum samples from: 1W = 1-7 days; 2W = 8-14 days; 3W = 15-21 days; 4W = 22-45 days; 3M = 46-135 days; 6M = 136-225 days; 9M = 226-315 days and 12M = 316-405 days/12-15M = 316-495). The arrows indicate time of vaccination post-onset of symptoms (see Supplementary Table 1 for specific days of vaccination and sample collections). Circles, non-vaccinated; squares, vaccinated with CoronaVac; triangles, vaccinated with BNT162b2. Conv: convalescent; Vacc: vaccine; 0: indicates pre-vaccination samples; 1: first dose; 2: second dose. Dashed line indicates the limit of detection (LOD) of the microneutralization assay. Every data point represents results from two technical replicates.

Figure 4

Neutralizing and anti-N antibody titres to SARS-CoV-2 in previously infected and naïve individuals before and after CoronaVac or BNT162b2 vaccination. nAb (b) and anti-N IgG (c) titres from 20 outpatient (42 samples) or 16 hospitalized (33 samples) individuals immunized with one or two doses of CoronaVac (30 participants) or one or two doses of BNT162b2 (6 participants) vaccines. nAb (b) and anti-N IgG (d) titres from naïve individuals after the first and second dose of CoronaVac (35 participants) or BNT162b2 (15 participants) vaccines, compared to nAb titres from convalescent patients (samples taken between days 10 and 28 from 28 outpatients (49 samples) and 34 hospitalized (58 samples) participants) and previously infected individuals (31 participants) before (31 samples) or after receiving two doses (25 samples) of the CoronaVac vaccine. Black lines represent the geometric mean titres (c) or end-point titres (d) and bars show the 95% confidence intervals. Statistics were performed using unpaired two-tailed Mann-Whitney test ((*P < 0·05; **P < 0·01; ***P < 0·001; ****P < 0·0001; ns, non-significant), excluding non-seroconverted data determined as outliers. Circles, non-vaccinated; squares, vaccinated with CoronaVac; triangles, vaccinated with BNT162b2. Conv: convalescent; Vacc: vaccine; 0: indicates pre-vaccination samples; 1: first dose; 2: second dose. Dashed line indicates the limit of detection (LOD) of the microneutralization assay and dotted line represents the limit of sensitivity (LOS) of ELISA. Every data point represents results from two technical replicates.