Abstract
ObjectivesIn the context of the Covid-19 pandemic, the fast development of vaccines with efficacy of around 95% preventing Covid-19 illness provides a unique opportunity to reduce the mortality associated with the pandemic. However, in the absence of efficacious prophylactic medications and few treatments for this infection, the induction of a fast and robust protective immunity is required for effective disease control, not only to prevent the disease but also the infection and shedding/transmission. The objective of our study was to analyze the level of specific humoral and cellular T-cell responses against the spike protein of SARS-CoV-2 induced by two mRNA-based vaccines (BNT162b2 and mRNA-1273), but also how long it takes after vaccination to induce these protective humoral and cellular immune responses.MethodsWe studied in 40 healthy (not previously infected) volunteers vaccinated with BNT162b2 or mRNA-1273 vaccines the presence of spike-specific IgG antibodies and SARS-CoV-2-specific T cells at 3, 7 and 14 days after receiving the second dose of the vaccine. The specific T-cell response was analyzed stimulating fresh whole blood from vaccinated volunteers with SARS-CoV-2 peptides and measuring the release of cytokines secreted by T cells in response to SARS-CoV-2 stimulation.ResultsOur results indicate that the immunization capacity of both vaccines is comparable. However, although both BNT162b2 and mRNA-1273 vaccines can induce early B-cell and T-cell responses, these vaccine-mediated immune responses do not reach their maximum values until 14 days after completing the vaccination schedule.ConclusionThis refractory period in the induction of specific immunity observed after completing the vaccination could constitute a window of higher infection risk, which could explain some emerging cases of SARS-CoV-2 infection in vaccinated people.
Highlights
The current Covid-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused more than 3 million deaths and enormous economic and social upheaval internationally
Several recent articles describe that mRNA-based vaccines elicit neutralizing antibodies that persist for several months
There is little information about the degree of specific T-cell responses induced by the vaccination and how long it takes after vaccination to induce protective humoral and cellular immune responses
Summary
The current Covid-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused more than 3 million deaths and enormous economic and social upheaval internationally. An unprecedented research effort has resulted in the fast development of Covid-19 vaccines in less than one year, and more than 80 vaccine candidates are in clinical development at present [1, 2]. Two of the vaccines developed, BNT162b2 (PfizerBioNTech) and mRNA-1273 (Moderna), are based on encapsulated mRNA encoding as the target antigen the spike (S) glycoprotein of the virus, and they are being massively administered around the world. Initial clinical trials employing these two vaccines report efficacy of around 95% preventing Covid-19 illness. In the case of BNT162b2, the primary endpoint was the efficacy of the vaccine against Covid-19 with onset at least 7 days after the second dose [3]. Regarding mRNA-1273 vaccine, the primary endpoint was the vaccine’s efficacy in preventing the first occurrence of symptomatic Covid-19 with onset at least 14 days after the second injection [4]
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