Comparing SARS-CoV-2 neutralizing antibody levels in convalescent unvaccinated, convalescent vaccinated, and naive vaccinated subjects

Post COVID-19 vaccination binding and neutralizing antibody with or without previous infection: An 18-month longitudinal study in Indonesia

Due to the persisting development of SARS-CoV-2 variants, studies on the kinetics, duration, and function of antibodies are essential for vaccine development and long-term immunity prediction. This longitudinal study examined post-vaccination antibody responses in people after receiving CoronaVac or ChAdOx1 vaccines with or without a history of SARS-CoV-2 infection. Conducted in Indonesia between August 2021 and May 2023, this study involved 121 participants divided into two groups based on the received vaccine types and monitored for 18 months post-second dose vaccination by assessing the binding antibody (BAb) level and neutralizing antibody (NAb) inhibition rate at six time points. The study also documented the participants' age, gender, and body mass index (BMI). Before the first dose vaccination, 85 (70.2%) participants were reactive BAb (defined by BAb level ≥50 AU/mL) indicating a history of infection. In the CoronaVac group, only 53.1% were reactive BAb. However, 100% of participants were positive NAb (defined by NAb inhibition rate ≥30%), which indicates a past history of infection with low initial or rapidly decreasing BAb levels. In the ChAdOx1 group, 81.9% of participants were reactive, while only 54.2% were positive NAb, suggesting a recent infection with a high BAb level but a relatively low NAb inhibition rate. During the 18 months post-second dose vaccination, the BAb levels fluctuated. However, 100% of participants were positive NAb. No significant difference in antibody response was documented among participants with or without infection history. Also, no significant impact was presented by the factors of sex, age, and BMI. The findings highlight the crucial of the vaccine in public health and how vaccination strategies could be optimized effectively during and after the post-pandemic.

Neutralization Testing-based Immunogenicity Analysis of Recent Prevalent Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Sublineages

Although WHO declared the end of the public health emergency for coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), XBB lineages continue to evolve and emerge globally. In particular, XBB.1.5 and XBB.1.16 are raising concerns because of their high immune evasion, leading to apprehensions regarding vaccine efficacy reduction and potential reinfection. We aimed to investigate the COVID-19 outbreak in Korea and predict the likelihood of reinfection by testing neutralizing activity against live viruses from the S clade and 19 Omicron sublineages. We found a significant risk of infection with the currently prevalent XBB lineage for individuals who were either vaccinated early or infected during the initial Omicron outbreak. Vaccinated individuals were better equipped than unvaccinated individuals to produce neutralizing antibodies for other SARS-CoV-2 variants upon infection. Therefore, unvaccinated individuals do not easily develop neutralizing activity against other variants and face the highest risk of reinfection by the XBB lineage. Our study provides important information to facilitate the development of strategies for monitoring populations that would be the most susceptible to new COVID-19 outbreaks.

Longitudinal Analysis of Antibody Response Following SARS-CoV-2 Infection Depending on Disease Severity: A Prospective Cohort Study

OBJECTIVE

Severe coronavirus disease 19 (COVID-19) is characterized by a dysregulated inflammatory response, with humoral immunity playing a central role in the disease course. The objective of this study was to assess the immune response and the effects of vaccination in recovered individuals with variable disease severity up to one year following natural infection.

METHODS

A prospective cohort study was conducted including patients with laboratory-confirmed COVID-19. Disease severity was classified as mild, moderate, and severe based on clinical presentation and outcomes. Anti-RBD (receptor binding domain) and neutralizing antibodies were evaluated at multiple timepoints during the first year after COVID-19 diagnosis.

RESULTS

A total of 106 patients were included; of them, 28 were diagnosed with mild, 38 with moderate, and 40 with severe disease. At least one vaccine dose was administered in 58 individuals during the follow-up. Participants with mild disease presented significantly lower anti-RBD and neutralizing antibodies compared to those with moderate and severe disease up to the 3rd and 6th months after the infection, respectively. After adjusting for covariates, in the third month, severe COVID-19 was associated with significantly higher anti-RBD (β: 563.09; 95% confidence intervals (CI): 257.02 to 869.17) and neutralizing (β: 21.47; 95% CI: 12.04 to 30.90) antibodies. Among vaccinated individuals, at the 12th month, a history of moderate disease was associated with significantly higher anti-RBD levels (β: 5615.19; 95% CI: 657.92 to 10,572.46).

CONCLUSIONS

Severe COVID-19 is associated with higher anti-RBD and neutralizing antibodies up to 6 months after the infection. Vaccination of recovered patients is associated with a remarkable augmentation of antibody titers up to one year after COVID-19 diagnosis, regardless of disease severity.