Study of antibody responses to COVID-19 mRNA vaccine in convalescents

Amid a COVID-19 pandemic well into its second year, most developed countries are implementing effective vaccination campaigns against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) to reduce the spread of the infection.

In December 2020, the Food and Drug Administration granted emergency use of two messenger RNA (mRNA) vaccines developed by Pfizer-BioNTech and Moderna to protect against severe acute respiratory syndrome coronavirus 2 (SARS-CoV- 2) – the agent responsible for the ongoing COVID-19 pandemic.

Phase 3 clinical trials of these vaccines have previously shown 94-95% efficacy in preventing COVID-19 and nearly 100% efficacy in protecting against serious illness.

In addition to clinical trials conducted to determine the safety and efficacy of mRNA vaccines, additional studies have begun to describe the serologic response to vaccines under “real world” conditions, particularly with the appearance of variants of the vaccine. SARS-CoV-2 and case reports. vaccine escape.

“While the initial focus may be on overall antibody levels and differences in antibody response in previously seropositive versus seronegative vaccines, other humoral antibody response factors need to be taken into account. says the team at the Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York.

The presence of neutralizing antibodies in people who have previously been exposed to SARS-CoV-2 compared to those who have not, and avidity for binding are two factors that help determine the quality of the antibody response. .

This study included the assessment of total antibody levels, antibody avidity, and neutralizing antibody levels in 49 uninfected vaccinated healthcare workers (NaïveVax) and 19 previously infected and vaccinated healthcare workers (RecoVax ). This response was again compared to the normal post-infection antibody response in 160 unvaccinated patients with mild symptoms (OutPtNoVax) and 122 unvaccinated acutely infected patients (HospoNoVax) at the onset of the pandemic.

A pre-printed version of the research paper is available on the website medRxiv* server, while the article is subject to peer review.

What did the study consist of?

The study included a retrospective and prospective study of individuals. In the retrospective study, serum was collected from patients with mild symptoms and patients with acute infections. These sera were then frozen for future analysis.

A prospective study was carried out in vaccinated subjects. In this study, blood samples were taken from participants during the first week after receiving the first dose of Pfizer mRNA vaccine and after two and four weeks from each dose of vaccine. Participants were also asked to donate blood samples three months and six months after the first dose of the vaccine.

Then, the SARS-CoV-2 total receptor binding domain (RBD) antibody (Tab), avidity test and neutralizing antibody test were performed. The Roche Elecsys Anti-SARS-CoV-2S assay and N-antigen assay were also performed to determine the levels of core antigen and spike protein antibodies in serum samples.

What did the study find?

The results showed that previously infected vaccinated individuals exhibited a rapid antibody response within days of receiving the first dose. The antibody level persisted for up to six months after vaccination. The antibody response did not increase further after the second dose for this population.

Dynamics of anti-SARS-CoV-2 antibody response after vaccination or infection using regression models. The levels of TAb (A), SNAb (B), and avidity (C) are displayed over time. A total of 686 data points were plotted from 19 RecoVax individuals (red), 49 NaiveVax individuals (blue) and 122 HospNoVax patients (green). All participants received the second dose 21 days after the first dose. The trend in antibody level over time has been described by applying Muggeo’s method of estimating regression models with unknown breakpoints to estimate points of change over time in trends.

“This contrasts with the other cohorts, where the TAb levels never fully matched RecoVax and in some cases declined,” the team explains.

Neutralizing antibody levels for the RecoVax group were higher than all other groups. They reached a maximum level after the first dose of vaccine and remained at this level for up to 6 months after vaccination.

The avidity of the RecoVax group was highest compared to the other groups, and this level was maintained throughout the six-month follow-up period.

“Nonetheless, the continued maturation of NaïveVax’s greed reached a similar level of greed approximately 6 months after D1,” the team explains.

What did the authors conclude?

The researchers concluded that two doses of the mRNA vaccine in NaïveVax individuals provide the same response as one dose of vaccine in RecoVax individuals.

“Individuals with mild symptoms of COVID19 (OutPtNoVax) generally maintained lower antibody levels than those of the vaccinated cohorts, in particular justifying vaccination despite a previous infection”, explains the team.

It can also be concluded that since only one dose of maximal immune response elicited by the vaccine in RecoVax individuals, this dose can be considered sufficient for them.

“Long-term monitoring of antibody titers of individuals (as is the case with hepatitis B or MMR vaccines), as well as monitoring of neutralizing activity and avidity, may be cautious to determine vaccine efficacy and the need for future booster vaccines, ”the team added. .

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.

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About Hector Hedgepeth

Hector Hedgepeth

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