Although we have made the case that antibodies may not be essential to deal with the virus, it is clear that antibodies are centrally important in limiting infection. This can be seen in this Russian study. If you made antibodies after infection you did OK and much better than if you only made T cell responses
Ivan Molodtso et al .A prospective study of the protective effect of SARS-CoV-2-specific antibodies and T cells in Moscow residents MedRXiv doi: https://doi.org/10.1101/2021.08.19.21262278 Background: Coronavirus disease COVID-19 has spread worldwide extremely rapidly. Although
many individuals have been infected and have cleared the virus, developing virus-specific
antibodies and effector/memory T cells, an important question still to be answered is what levels of
T cell and antibody responses are sufficient to protect from the infection.
Methods: In 5,340 Moscow residents, we evaluated the anti-SARS-CoV-2 IgM/IgG titers and the
frequencies of the T cells specific to the nucleocapsid, membrane, and spike proteins of SARSCoV-2, using IFNγ ELISpot, and we also evaluated the fractions of virus-specific CD4+
and CD8+ T cells using intracellular staining of IFNγ and IL2 followed by flow cytometry. Furthermore, we
analyzed the post-inclusion COVID-19 rates as a function of the assessed antibody and T cell
responses. Results: We showed that T cell and antibody responses are closely interconnected and commonly
are induced concurrently. Individuals positive for both antibody and T cell immunities
demonstrated the highest levels of protectivity against the SARS-CoV-2 infection, indistinguishably from individuals with antibody response only.
Meanwhile, individuals with T cell response only demonstrated slightly higher protectivity than individuals without both types of immunity, as measured from N-protein–specific or CD4+IL2+ T cells. However, these individuals were characterized by higher IgG titers than individuals without any immunity, although the titrres were below the seropositivity cut-off.
Conclusions: The results of the study indicated the advantage of serology testing over the analysis
of T cell responses for the prediction of SARS-CoV-2 infection rates on a populational level.
So this study argues that a neutralizing antibody response is important in stopping infection and as seen below the level of neutralizing antibodies predict the level of protection against symptomatic covid
Khoury DS, Cromer D, Reynaldi A, Schlub TE, Wheatley AK, Juno JA, Subbarao K, Kent SJ, Triccas JA, Davenport MP. Neutralizing antibody levels are highly predictive of immune protection from symptomatic SARS-CoV-2 infection. Nat Med. 2021;27(7):1205-1211.Predictive models of immune protection from COVID-19 are urgently needed to identify correlates of protection to assist in the future deployment of vaccines. To address this, we analyzed the relationship between in vitro neutralization levels and the observed protection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection using data from seven current vaccines and from convalescent cohorts. We estimated the neutralization level for 50% protection against detectable SARS-CoV-2 infection to be 20.2% of the mean convalescent level (95% confidence interval (CI) = 14.4-28.4%). The estimated neutralization level required for 50% protection from severe infection was significantly lower (3% of the mean convalescent level; 95% CI = 0.7-13%, P = 0.0004). Modeling of the decay of the neutralization titer over the first 250 d after immunization predicts that a significant loss in protection from SARS-CoV-2 infection will occur, although protection from severe disease should be largely retained. Neutralization titers against some SARS-CoV-2 variants of concern are reduced compared with the vaccine strain, and our model predicts the relationship between neutralization and efficacy against viral variants. Here, we show that neutralization level is highly predictive of immune protection, and provide an evidence-based model of SARS-CoV-2 immune protection that will assist in developing vaccine strategies to control the future trajectory of the pandemic.
This study again argues that antibody levels correlate with protection.
Shuo Feng, Daniel J. Phillips, Thomas White, Homesh Sayal, Parvinder K. Aley, Sagida Bibi, Christina Dold, Michelle Fuskova, Sarah C. Gilbert, Ian Hirsch, Holly E. Humphries, Brett Jepson, Elizabeth J. Kelly, Emma Plested, Kathryn Shoemaker, Kelly M. Thomas, Johan Vekemans, Tonya L. Villafana, Teresa Lambe, Andrew J Pollard, Merryn Voysey, the Oxford COVID Vaccine Trial Group. Correlates of protection against symptomatic and asymptomatic SARS-CoV-2 infection. medRxiv 2021.06.21.21258528; doi: https://doi.org/10.1101/2021.06.21.21258528
Background Although 6 COVID-19 vaccines have been approved by the World Health Organisation as of 16th June 2021, global supply remains limited. An understanding of the immune response associated with protection could facilitate rapid licensure of new vaccines.
Methods Data from a randomised efficacy trial of ChAdOx1 nCoV-19 (AZD1222) vaccine in the UK was analysed to determine the antibody levels associated with protection against SARS-CoV-2. Anti-spike and anti-RBD IgG by multiplex immunoassay, pseudovirus and live neutralising antibody at 28 days after the second dose were measured in infected and non-infected vaccine recipients. Weighted generalised additive models for binary data were applied to symptomatic and asymptomatic SARS-CoV-2 infection data from ChAdOx1 nCoV-19 recipients. Cubic spline smoothed log antibody levels, and weights were applied to account for potential selection bias in sample processing. Models were adjusted for baseline risk of exposure to SARS-CoV-2 infection.
Results Higher levels of all immune markers were correlated with a reduced risk of symptomatic infection. Vaccine efficacy of 80% against primary symptomatic COVID-19 was achieved with an antibody level of 40923 (95% CI: 16748, 125017) and 63383 (95% CI: 16903, not computed (NC)) for anti-spike and anti-RBD, and 185 (95% CI: NC, NC) and 247 (95% CI: 101, NC) for pseudo- and live-neutralisation assays respectively. Antibody responses did not correlate with overall protection against asymptomatic infection.
Conclusions Correlates of protection can be used to bridge to new populations using validated assays. The data can be used to extrapolate efficacy estimates for new vaccines where large efficacy trials cannot be conducted. More work is needed to assess correlates for emerging variants.
General Disclaimer: Please note that the opinions expressed here are those of the author and do not necessarily reflect the positions of the Barts and The London School of Medicine and Dentistry nor Barts Health NHS Trust and are not meant to be interpreted as personal clinical advice.