Vaccination or infection – which offers most protective immunity?
Published: January 26, 2022
Amidst 2021, the first COVID-19 vaccines rollout gave hope to tackle the ongoing pandemic. Due to a favorable safety profile and excellent efficacy, it was hoped that vaccines would reduce severe symptomatic infection, hospitalization and death. However, uncontrolled spreading of SARS-CoV-2, the causative agent, led to emergence of new virus variants because of naturally acquired mutations. These genetic changes often occurred in the viral spike protein, thereby potentially evading vaccine-induced protection. If new SARS-CoV-2 variants are associated with increased infectivity and disease severity, the World Health Organization (WHO) classifies these as Variants of Concern (VOCs), which require careful evaluation of immunity in vaccinated and recovered individuals.
In a recent article published in The Journal of Allergy and Clinical Immunology (JACI), Lafon/Jäger et al. studied humoral immune responses and virus neutralization abilities from patients who recovered from COVID-19 infection and vaccinated individuals. In addition to serum spike-specific IgG and IgA and Receptor Binding Domain (RBD)-specific antibodies, neutralization ability against different strains of SARS-CoV-2 VOC including the wild type (WT) strain, Alpha-, Alpha-E484K, Beta- and Delta were investigated. Cohorts included individuals vaccinated with the three major vaccines approved in EU/EEA by the time of the study. Individuals were analyzed one month after the second dose of BNT162b2 by Pfizer/BioNTech (n=31), mRNA-1273 by Moderna (n=23) or ChAdOx1 by AstraZeneca (n=33). Convalescent cohorts included participants who had recovered from SARS-CoV-2 WT infection (n=29) without any prior immunization.
The authors reported a high IgG response (as measured by commercially available ELISA tests) against the viral spike protein, containing RBD, in all vaccinated participants, with the highest titers detected for mRNA-based vaccines (BNT162b2 and mRNA-1273) followed by vector-based vaccine. Interestingly, convalescent individuals had on average less IgG and higher variation of antibody titers within the cohort. Highest serum IgA titers were found in individuals immunized with mRNA-based vaccines compared to vector-based vaccine ChAdOx1 or convalescent patients. Potential immune escape of VOCs due to impaired antibody binding was analyzed using sera from vaccinated and convalescent individuals. They found that the majority of vaccinees could neutralize all VOCs, whereas recovered patients only showed positive neutralization against SARS-CoV-2 WT, Alpha and Beta variant, but not Alpha-E484k or Delta variants. In fact, neutralization titers against these two VOCs were lower in all vaccine groups, but individuals vaccinated with mRNA-1273 elicited the highest protection. For both vaccinees and convalescent individuals, significant positive correlation between antibody titers and neutralizing antibody titers was found.
Due to the fact that SARS-CoV-2 variants continue to arise, comprehensive understanding of their ability to bypass vaccine-induced immunity is currently of utmost importance, especially since these platforms have been designed against the WT strain. The lower and heterogeneous range of antibody or neutralization titers in COVID-19-convalescent patients without any prior vaccination, makes it more difficult to assess the level of protection of this cohort. In comparison, all three vaccine groups elicited robust and more homogeneous humoral responses; the mRNA-based vaccines induced highest neutralizing antibodies against VOCs. This study gives insight on vaccine- and infection-induced humoral immunity against VOCs and illustrated the production of SARS-CoV-2-specific IgA after the second dose of three major COVID-19 vaccines.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.
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