Antibody Response to SARS-CoV-2 is Associated with Long-term Clinical Outcome in Patients with COVID-19: a Longitudinal Study

Abstract

Background: The relationship of host immune response and viral replication with health outcomes in patients with COVID-19 remains to be defined. We aimed to characterize the medium and long-term clinical, virological, and serological outcomes after hospitalization for COVID-19, and to identify predictors of long-COVID.

Methods: Prospective, longitudinal study conducted in COVID-19 patients confirmed by RT-PCR. Serial blood and nasopharyngeal samples (NPS) were obtained for measuring SARS-CoV-2 RNA and S-IgG/N-IgG antibodies during hospital stay, and at 1, 2, and 6 months post-discharge. Genome sequencing was performed where appropriate. Patients filled out a COVID-19 symptom questionnaire (CSQ) at 2-month and 6-month visits, and those with highest scores were characterized.

Results: Of 146 patients (60% male, median age 64 years) followed-up, 20.6% required hospital readmission and 5.5% died. At 2 months and 6 months, 9.6% and 7.8% patients, respectively, reported moderate/severe persistent symptoms. SARS-CoV-2 RT-PCR was positive in NPS in 11.8% (median Ct = 38) and 3% (median Ct = 36) patients at 2 months and 6 months, respectively, but no reinfections were demonstrated. Antibody titers gradually waned, with seroreversion occurring at 6 months in 27 (27.6%) patients for N-IgG and in 6 (6%) for S-IgG. Adjusted 2-month predictors of the highest CSQ scores (OR [95%CI]) were lower peak S-IgG (0.80 [0.66-0.94]) and higher WHO severity score (2.57 [1.20-5.86]); 6-month predictors were lower peak S-IgG (0.89 [0.79-0.99]) and female sex (2.41 [1.20-4.82]); no association was found with prolonged viral RNA shedding.

Conclusions: Long-COVID is associated with weak anti-SARS-CoV-2 antibody response, severity of illness, and female gender. Late clinical events and persistent symptoms in the medium and long term occur in a significant proportion of patients hospitalized for COVID-19.

Keywords: COVID-19; SARS-CoV-2; antibody response; long-COVID; viral shedding.

Fig. 1

Temporal changes in symptom scores and serum levels of biomarkers during follow-up. Panel A shows the scores of self-reported general, respiratory, and gastrointestinal symptoms included in the COVID-19 symptoms questionnaire at baseline, 2 months and 6 months. Panels B, C, D, E represent the temporal changes in the serum levels of C-reactive protein (panel B), interleukin-6 (panel C), ferritin (panel D), and D-dimer (panel E) since COVID-19 diagnosis. Panel A: General symptoms include fatigue, myalgia, sweating, headache; respiratory symptoms include cough, difficulty breathing, nasal congestion, sore throat, anosmia; gastrointestinal symptoms include diarrhea, vomiting, abdominal pain. ^*Pearson’s Chi-squared test P value < 0.05. Panels B, C, D, E: Each dot represents a serum biomarker value in an individual subject since hospital admission, with interpolation line and 90% confidence interval. Biomarkers normal ranges: C-reactive protein, below 5 mg/L; IL-6, below 7 pg/mL; ferritin, normal ranges values depend on patient’s sex and age (17–464 ƞr/mL for men older than 20 years and 6–137 ƞg/mL and 11–264 ƞg/mL for women between 20 and 50 and older than 50 years old, respectively); D-dimer, below 0.5 μg/mL. IL-6, interleukin-6

Fig. 2

SARS-CoV-2 sero-virological changes during follow-up. Panel A: SARS-CoV-2 RT-PCR test results during follow-up in the entire cohort. Panel B: Temporal changes in anti-SARS-CoV-2 surface S1 domain of the spike protein and nucleocapsid protein IgG antibodies. Panel A: Each horizontal level represents the RT-PCR SARS-CoV-2 results for each patient in the cohort throughout follow-up, since the first positive result to the last available one. Red dots represent positive results and green dots negative results. Black dots mark those patients who died and time of death since the first positive SARS-CoV-2 RT-PCR result. Colored lines join two consecutive dots in the same patient with the same result and less than 90 days between dots. Patient #143 moved to another country after discharge. Patients #139, #142, and #145 could only be reached by phone. Patients #136 and #137 refused to have a new nasopharyngeal sample taken but agreed to continue with the clinical follow-up. RT-PCR, reverse transcriptase-polymerase chain reaction. Panel B: Each dot represents an S-IgG (continuous line and circle symbols) or N-IgG (dashed line and plus symbols) value in an individual subject, with interpolation line and 90% confidence interval. S/CO, absorbance/cut-off; S-IgG, S-IgG antibody against the SARS-CoV-2 surface S1 domain of the spike protein; N-IgG, antibody against the SARS-CoV-2 internal nucleocapsid protein. Positive S/CO >1.1

Fig. 3

Temporal changes in SARS-CoV-2 IgG antibodies and serum inflammatory biomarkers during follow-up by symptomatic status. Serum levels of S-IgG (panel A), N-IgG (panel B), C-reactive protein (panel C), interleukin-6 (panel D), ferritin (panel E), and D-dimer (panel F) during follow-up. Dashed lines and plus symbols represent individuals with the highest scores in COVID-19 symptoms questionnaire; continuous lines and circle symbols represent all other patients filling the questionnaire. S-IgG, IgG antibody against the SARS-CoV-2 surface S1 domain of the spike protein; N-IgG, IgG antibody against the SARS-CoV-2 internal nucleocapsid protein; S/CO, absorbance/cut-off. P value for the comparison between groups according to the score in COVID-19 symptoms questionnaire. Positive S/CO >1.1

Fig. 4

Predictors of the highest scores in COVID-19 symptoms questionnaire in multivariate regression logistic model at 2-month and 6-month follow-up. Panel A represents 2-month, and panel B 6-month follow-up. WHO, World Health Organization; S-IgG, IgG antibody against the SARS-CoV-2 surface S1 domain of the spike protein; S/CO, absorbance/cut-off; RT-PCR, reverse transcriptase-polymerase chain reaction. ^*P value < 0.05