The potency of the 3-dose coronavirus disease 2019 (COVID-19) vaccination against severe acute respiratory system syndrome coronavirus 2 (SARS-CoV-2) and it is variants continues to be described at length in research conducted recently. The research report is presently on the bioRxiv* preprint server.
COVID-19 vaccines developed inside a very short time have made it feasible to manage the ever-growing pandemic trajectory and unparalleled healthcare damage brought on by SARS-CoV-2 globally. Several kinds of vaccines happen to be developed, including mRNA-based and viral vector-based vaccines.
With enormous initial success, a loss of vaccine effectiveness with time continues to be felt by many countries around the globe, especially due to the emergence of recent and much more immunologically potent viral variants.
To enhance vaccine effectiveness, another booster vaccination continues to be introduced within the global COVID-19 vaccination campaigns. Numerous studies conducted in tangible-world setups have affirmatively highlighted the general improvement in vaccine effectiveness following booster vaccination.
In the present study, scientists have given an in depth summary of the humoral and cellular responses caused by three-dose homologous or heterologous COVID-19 vaccination in infection-naïve healthy individuals.
Humoral immune response caused by COVID-19 vaccination
The research was conducted on as many as 20 individuals. Bloodstream samples collected in the participants following the first, second, and third vaccination were tested for anti-spike S1, S2, and receptor-binding domain (RBD) IgG, IgA, and IgM antibodies.
The findings revealed detectable anti-spike IgG levels following the first vaccination. The amount elevated considerably following the second vaccines. However, a substantial loss of antibody levels was observed six several weeks following the second vaccination.
The 3rd vaccination helped prevent further loss of antibody levels. Particularly, both second and third vaccination caused similar amounts of anti-spike IgG antibodies within the bloodstream.
Regarding IgA-specific anti-spike antibodies, a considerably elevated level was noticed in the bloodstream following the second and third vaccination. However, the antibody levels varied significantly among participants.
An induction within the IgM-specific antibody level was noticed in the bloodstream following the first vaccination, with anti-RBD antibodies showing greater levels than anti-S1 and anti-S2 antibodies.
Antibody-inhibitory capacity was assessed to look for the ability of anti-SARS-CoV-2 antibodies to hinder viral spike–host angiotensin-converting enzyme 2 (ACE2) interaction. The findings revealed a substantial induction in antibody-inhibitory capacity following the third vaccination against wildtype SARS-CoV-2 and it is variants alpha, beta, gamma, delta, and omicron. However, the neutralizing effectiveness of antibodies caused through the third vaccination was relatively lower from the omicron variant.
Regarding type and regimen of vaccination, no factor in antibody levels and antibody-inhibitory capacity was observed following the third dose between recipients of homologous (three doses of mRNA vaccine) and heterologous vaccination (one dose of adenovirus vector vaccine adopted by two doses of mRNA vaccine).
Cellular immune response caused by COVID-19 vaccination
A higher individual variability within the absolute quantity of B and T cell subsets was observed among recipients of COVID-19 vaccination. Particularly, the introduction of spike-specific memory T cells was observed after consecutive COVID-19 vaccinations.
Following the first vaccination, recipients of heterologous vaccination exhibited a greater proportion of memory T cells and B cells than recipients of homologous vaccination. However, no such difference was observed following a second and third vaccinations.
The dynamics of T cell response were further assessed in people with three-dose vaccination with and without breakthrough SARS-CoV-2 infection. Both groups demonstrated effective memory T cell formation. However, a greater secretion of interferon-gamma was noticed in people with breakthrough infection.
Particularly, people with breakthrough infection demonstrated a greater ability than infection-naïve vaccinated visitors to secrete an array of cytokines and chemokines connected with T cell activation.
Overall, these bits of information indicate that SARS-CoV-2 breakthrough infections induce broader and much more specific T cell response when compared with triple vaccination.
The research highlights the potency of three-dose COVID-19 vaccination against SARS-CoV-2 and it is variants. The 3rd booster dose of COVID-19 vaccines is extremely good at inducing robust humoral and cellular immune responses in infection-naïve individuals.
The 3rd vaccination is especially essential to boost the amounts of neutralizing antibodies against a large-number of viral variants, including omicron.
Importantly, the research signifies that homologous and heterologous vaccinations work similarly after third dose when it comes to inducing humoral and cellular immune responses.
bioRxiv publishes preliminary scientific reports that aren’t peer-reviewed and, therefore, shouldn’t be considered as conclusive, guide clinical practice/health-related behavior, or treated as established information.