Bilich et al showed that IgG and IgA antibody responses declined during the six-month follow-up, raising concerns that humoral immunity against SARS-CoV-2 may not provide longterm protection. Anti-S1 antibody responses decrease over time, whereas anti-nucleocapsid antibody titres persist, this is important in the context of vaccine development focusing on the induction of immune responses to the RBD of the spike protein.

Bilich T, Nelde A, Heitmann JS, Maringer Y, Roerden M, Bauer J, et al. T cell and antibody kinetics delineate SARS-CoV-2 peptides mediating long-term immune responses in COVID-19 convalescent individuals. Science Translational Medicine. 2021:eabf7517.

Zhou et al showed that serum IgM and IgG, especially in patients with moderate‐to‐high levels, declined significantly between week 4 to 10 after illness onset. Paper suggests that a decline in IgM may be an indicator of virus clearance. Although IgG levels declined to low levels within 11 weeks, they remained detectable.

Figueiredo‐Campos et al quantified IgM, IgG and IgA and showed that although titres reduced, IgG antibodies remained robust with confirmed neutralisation activity for up to 6 months

Zhou W, Xu X, Chang Z, Wang H, Zhong X, Tong X, Liu T, Li Y. The dynamic changes of serum IgM and IgG against SARS-CoV-2 in patients with COVID-19. J Med Virol. 2021 Feb;93(2):924-933. doi: 10.1002/jmv.26353. Epub 2020 Sep 28. PMID: 32706425; PMCID: PMC7404900.

Figueiredo‐Campos, P., Blankenhaus, B., Mota, C., Gomes, A., Serrano, M., Ariotti, S., Costa, C., Nunes‐Cabaço, H., Mendes, A.M., Gaspar, P., Pereira‐Santos, M.C., Rodrigues, F., Condeço, J., Escoval, M.A., Santos, M., Ramirez, M., Melo‐Cristino, J., Simas, J.P., Vasconcelos, E., Afonso, Â. and Veldhoen, M. (2020), Seroprevalence of anti‐SARS‐CoV‐2 antibodies in COVID‐19 patients and healthy volunteers up to 6 months post disease onset. Eur. J. Immunol., 50: 2025-2040. https://doi.org/10.1002/eji.202048970