AUTHOR=Carvalho Álvaro , Henriques Ana Rita , Queirós Paula , Rodrigues Joana , Mendonça Nuno , Rodrigues Ana Maria , Canhão Helena , de Sousa Germano , Antunes Francisco , Guimarães Miguel 

TITLE=Persistence of IgG COVID-19 antibodies: A longitudinal analysis

JOURNAL=Frontiers in Public Health

VOLUME=Volume 10 - 2022

YEAR=2023

URL=https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2022.1069898

DOI=10.3389/fpubh.2022.1069898

ISSN=2296-2565

ABSTRACT=Background and Aim:
The kinetics of antibody production in response to coronavirus disease 2019 (COVID-19) infection is not well defined yet. This study aimed to evaluate the antibody responses to SARS-CoV-2 and its dynamics during 9-months in a cohort of patients infected during the first phase of the pandemic. As a secondary aim, it was intended to evaluate the factors associated with different concentrations of IgG antibodies.
Methods:
A prospective cohort study was conducted from June 2020 to January 2021. This study recruited a convenience sample of adult individuals who where recently diagnosed with COVID-19 and were living in mainland Portugal. A total of 1695 blood samples were collected from 585 recovered COVID-19 patients up to nine months after SARS-CoV-2 acute infection. A blood sample was collected at baseline and three, six and nine months after SARS-CoV-2 acute infection to assess the concentration of IgG antibody  against SARS-CoV-2.
Results:  
The positivity rate of IgG reached 77.7% in the first three months after symptom onset. The IgG persists at all subsequent follow-up time points, which was 87.7% and 89.2% in the sixth and ninth months after symptom onset, respectively.
Three distinct kinetics of antibody response were found within the nine months after infection. Kinetic 1 (K1) was characterized by a constant low IgG antibody concentration kinetic (group size: 65.2%); kinetic 2 (K2), composed by constant moderate IgG kinetic  (group size: 27.5%) and kinetic 3 (K3) characterised by higher IgG kinetic (group size: 7.3%). People with ≥ 56 years old (OR: 3.33; CI 95%: [1.64; 6.67]; p-value: 0.001) and symptomatic COVID-19 (OR: 2.08; CI 95%: [1.08; 4.00]; p-value: 0.031) had higher odds of a “Moderate IgG kinetic”. No significant association were found regarding the "Higher IgG kinetic".  

Conclusion:
Our results demonstrate a lasting anti-spike (anti-S) IgG antibody response at least nine months after infection in the majority of patients with COVID-19. Younger participants with asymptomatic disease have lower IgG antibody positivity and possibly more susceptible to reinfection. This information contributes to expanding knowledge of SARS-CoV-2 immune response and has direct implications in the adoption of preventive strategies and public health policies.