Safety and immunogenicity of the FINLAY-FR-1A vaccine in COVID-19 convalescent participants: an open-label phase 2a and double-blind, randomised, placebo-controlled, phase 2b, seamless, clinical trial

Overcoming colonialism in pathogen genomics

Historical legacies of colonialism affect the distribution and control of scientific knowledge today, including within the pathogen genomics field, which remains dominated by high-income countries (HICs). We discuss the imperatives for decolonising pathogen genomics, including the need for more equitable representation, collaboration, and capacity-strengthening, and the shared responsibilities that both low-income and middle-income countries (LMICs) and HICs have in this endeavour. By highlighting examples from LMICs, we illuminate the pathways and challenges that researchers in LMICs face in the bid to gain autonomy in this crucial domain. Recognising the inherent value of local expertise and resources, we argue for a more inclusive, globally collaborative approach to pathogen genomics. Such an approach not only fosters scientific growth and innovation, but also strengthens global health security by equipping all nations with the tools needed to respond to health crises.

Role of N343 glycosylation on the SARS-CoV-2 S RBD structure and co-receptor binding across variants of concern

Glycosylation of the SARS-CoV-2 spike (S) protein represents a key target for viral evolution because it affects both viral evasion and fitness. Successful variations in the glycan shield are difficult to achieve though, as protein glycosylation is also critical to folding and structural stability. Within this framework, the identification of glycosylation sites that are structurally dispensable can provide insight into the evolutionary mechanisms of the shield and inform immune surveillance. In this work, we show through over 45 μs of cumulative sampling from conventional and enhanced molecular dynamics (MD) simulations, how the structure of the immunodominant S receptor binding domain (RBD) is regulated by N-glycosylation at N343 and how this glycan's structural role changes from WHu-1, alpha (B.1.1.7), and beta (B.1.351), to the delta (B.1.617.2), and omicron (BA.1 and BA.2.86) variants. More specifically, we find that the amphipathic nature of the N-glycan is instrumental to preserve the structural integrity of the RBD hydrophobic core and that loss of glycosylation at N343 triggers a specific and consistent conformational change. We show how this change allosterically regulates the conformation of the receptor binding motif (RBM) in the WHu-1, alpha, and beta RBDs, but not in the delta and omicron variants, due to mutations that reinforce the RBD architecture. In support of these findings, we show that the binding of the RBD to monosialylated ganglioside co-receptors is highly dependent on N343 glycosylation in the WHu-1, but not in the delta RBD, and that affinity changes significantly across VoCs. Ultimately, the molecular and functional insight we provide in this work reinforces our understanding of the role of glycosylation in protein structure and function and it also allows us to identify the structural constraints within which the glycosylation site at N343 can become a hotspot for mutations in the SARS-CoV-2 S glycan shield.

Real-world effectiveness of the heterologous SOBERANA-02 and SOBERANA-Plus vaccine scheme in 2-11 years-old children during the SARS-CoV-2 Omicron wave in Cuba: a longitudinal case-population study

Background

Increased pediatric COVID-19 occurrence due to the SARS-CoV-2 Omicron variant has raised concerns about the effectiveness of existing vaccines. The protection provided by the SOBERANA-02-Plus vaccination scheme against this variant has not yet been studied. We aimed to evaluate the scheme's effectiveness against symptomatic Omicron infection and severe disease in children.

Methods

In September 2021, Cuba implemented a mass pediatric immunization with the heterologous SOBERANA-02-Plus scheme: 2 doses of conjugated SOBERANA-02 followed by a heterologous SOBERANA-Plus dose. By December, before the Omicron outbreak, 95.4% of 2-18 years-old had been fully immunized. During the entire Omicron wave, we conducted a nationwide longitudinal post-vaccination case-population study to evaluate the real-world effectiveness of the SOBERANA-02-Plus scheme against symptomatic infection and severe disease in children without previous SARS-CoV-2 infection. The identification of COVID-19 cases relied on surveillance through first line services, which refer clinical suspects to pediatric hospitals where they are diagnosed based on a positive RT-PCR test. We defined the Incidence Rate ratio (IRR) as IRvaccinated age group/IRunvaccinated 1-year-old and calculated vaccine effectiveness as VE = (1-IRR)∗100%. 24 months of age being the 'eligible for vaccination' cut-off, we used a regression discontinuity approach to estimate effectiveness by contrasting incidence in all unvaccinated 1-year-old versus vaccinated 2-years-old. Estimates in the vaccinated 3-11 years-old are reported from a descriptive perspective.

Findings

We included 1,098,817 fully vaccinated 2-11 years-old and 98,342 not vaccinated 1-year-old children. During the 24-week Omicron wave, there were 7003/26,241,176 person-weeks symptomatic COVID-19 infections in the vaccinated group (38.2 per 105 person-weeks in 2-years-old and 25.5 per 105 person-weeks in 3-11 years-old) against 3577/2,312,273 (154.7 per 105 person-weeks) in the unvaccinated group. The observed overall vaccine effectiveness against symptomatic infection was 75.3% (95% CI, 73.5-77.0%) in 2-years-old children, and 83.5% (95% CI, 82.8-84.2%) in 3-11 years-old. It was somewhat lower during Omicron BA.1 then during Omicron BA.2 variant circulation, which took place 1-3 and 4-6 months after the end of the vaccination campaign. The effectiveness against severe symptomatic disease was 100.0% (95% CI not estimated) and 94.6% (95% CI, 82.0-98.6%) in the respective age groups. No child death from COVID-19 was observed.

Interpretation

Immunization of 2-11 years-old with the SOBERANA-02-Plus scheme provided strong protection against symptomatic and severe disease caused by the Omicron variant, which was sustained during the six months post-vaccination follow-up. Our results contrast with the observations in previous real-world vaccine effectiveness studies in children, which might be explained by the type of immunity a conjugated protein-based vaccine induces and the vaccination strategy used.

Funding

National Fund for Science and Technology (FONCI-CITMA-Cuba).

Increased antibody titers but induced T cell AICD and apoptosis response in COVID-19 convalescents by inactivated vaccine booster

It is urgently needed to evaluate the necessity and benefits of booster vaccination against the coronavirus 2 of the severe acute respiratory syndrome (SARS-CoV-2) Omicron to facilitate clinical decision-making for 2019 coronavirus disease (COVID-19) convalescents. We conducted a multicenter, prospective clinical trial (registration number: ChiCTR2100045810) in the first patients with COVID-19 from 28 January 2020 to 20 February 2020 to assess the long-term durability of neutralizing antibodies against live Omicron BA.5 and further assess the efficiency and safety of CoronaVac in the convalescent group. A total of 96 COVID-19 convalescents were enrolled in this study. Neutralizing antibody titers in convalescents were significantly reduced in 9-10 months. A dose-refreshing vaccination in 28 convalescents with an antibody titer below 96 significantly induced neutralizing antibodies against live Omicron by 4.84-fold. Meanwhile, the abundance of naive T cells increased dramatically, and TEMRA and TEM cells gradually decreased after vaccination. Activation-induced cell death and apoptosis-related genes were significantly elevated after vaccination in all T-cell subtypes. One-dose booster vaccination was effective in inducing a robust antibody response against SARS-CoV-2 Omicron in COVID-19 convalescents with low antibody titers. However, vaccine-mediated T-cell consumption and regeneration patterns may be detrimental to the antiviral response.IMPORTANCEThe globally dominant coronavirus 2 of the severe acute respiratory syndrome (SARS-CoV-2) Omicron variant raises the possibility of repeat infections among 2019 coronavirus disease (COVID-19) convalescents with low neutralizing antibody titers. The importance of this multicenter study lies in its evaluation of the long-term durability of neutralizing antibodies in COVID-19 convalescents and the efficacy of a booster vaccination against the live Omicron. The findings suggest that a one-dose booster vaccination is effective in inducing a robust antibody response against SARS-CoV-2 Omicron in convalescents with low antibody titers. However, the study also highlights the potential detrimental effects on the antiviral response due to vaccine-mediated T-cell consumption and regeneration patterns. These results are crucial for facilitating clinical decision-making for COVID-19 convalescents and informing public health policies regarding booster vaccinations.

Studying SARS-CoV-2 interactions using phage-displayed receptor binding domain as a model protein

SARS-CoV-2 receptor binding domain (RBD) mediates viral entry into human cells through its interaction with angiotensin converting enzyme 2 (ACE2). Most neutralizing antibodies elicited by infection or vaccination target this domain. Such a functional relevance, together with large RBD sequence variability arising during viral spreading, point to the need of exploring the complex landscape of interactions between RBD-derived variants, ACE2 and antibodies. The current work was aimed at developing a simple platform to do so. Biologically active and antigenic Wuhan-Hu-1 RBD, as well as mutated RBD variants found in nature, were successfully displayed on filamentous phages. Mutational scanning confirmed the global plasticity of the receptor binding motif within RBD, highlighted residues playing a critical role in receptor binding, and identified mutations strengthening the interaction. The ability of vaccine-induced antibodies to inhibit ACE2 binding of many mutated RBD variants, albeit at different extents, was shown. Amino acid replacements which could compromise such inhibitory potential were underscored. The expansion of our approach could be the starting point for a large-scale phage-based exploration of diversity within RBD of SARS-CoV-2 and related coronaviruses, useful to understand structure-function relationships, to engineer RBD proteins, and to anticipate changes to watch during viral evolution.

BioHabana 2022: Preventive and Immunotherapeutic Strategies Against COVID-19 and Cancer in Cuba

The convergence of life sciences with neurosciences, nanotechnology, data management, and engineering has caused a technological diversification of the biotechnology, pharmaceutical, and medical technology industries, including the phenomenon of digital transformation, which has given rise to the so-called Fourth Industrial Revolution (Industry 4.0). Confronting the COVID-19 pandemic revealed the outstanding response capacity of the scientific community and the biopharmaceutical industry, based on a multidisciplinary and interinstitutional approach that has achieved an unprecedented integration in the history of biomedical science. Cuba, a small country, with scarce material resources, has had remarkable success in controlling the disease, which also highlights the impact of social factors. This report presents a summary of the most relevant presentations of selected topics during the scientific meeting, "BioHabana 2022: Cancer Immunotherapy and the COVID-19 Pandemic," which was held in Havana Cuba in April 2022.

Comparative Immune Response after Vaccination with SOBERANA® 02 and SOBERANA® plus Heterologous Scheme and Natural Infection in Young Children

(1) Background: In children, SARS-CoV-2 infection is mostly accompanied by mild COVID-19 symptoms. However, multisystem inflammatory syndrome (MIS-C) and long-term sequelae are often severe complications. Therefore, the protection of the pediatric population against SARS-CoV-2 with effective vaccines is particularly important. Here, we compare the humoral and cellular immune responses elicited in children (n = 15, aged 5-11 years) vaccinated with the RBD-based vaccines SOBERANA® 02 and SOBERANA® Plus combined in a heterologous scheme with those from children (n = 10, aged 4-11 years) who recovered from mild symptomatic COVID-19. (2) Methods: Blood samples were taken 14 days after the last dose for vaccinated children and 45-60 days after the infection diagnosis for COVID-19 recovered children. Anti-RBD IgG and ACE2-RBD inhibition were assessed by ELISA; IgA, cytokines, and cytotoxic-related proteins were determined by multiplex assays. Total B and T cell subpopulations and IFN-γ release were measured by multiparametric flow cytometry using a large panel of antibodies after in vitro stimulation with S1 peptides. (3) Results: Significant higher levels of specific anti-RBD IgG and IgA and ACE2-RBD inhibition capacity were found in vaccinated children in comparison to COVID-19 recovered children. Th1-like and Th2-like CD4+ T cells were also significantly higher in vaccinated subjects. IFN-γ secretion was higher in central memory CD4+ T cells of COVID-19 recovered children, but no differences between both groups were found in the CD4+ and CD8+ T cell effector, terminal effector, and naïve T cell subpopulations. In contrast to low levels of IL-4, high levels of IL-2, IL-6, IFN-γ, and IL-10 suggest a predominant Th1 cell polarization. Cytotoxic-related proteins granzyme A and B, perforin, and granulin were also found in the supernatant after S1 stimulation in both vaccinated and recovered children. (4) Conclusions: Vaccination with the heterologous scheme of SOBERANA® 02/SOBERANA® Plus induces a stronger antibody and cellular immune response compared to natural infections in young children.

An overview of protein-based SARS-CoV-2 vaccines

SARS-CoV-2 resulted in the COVID-19 pandemic which, to date, has resulted in an estimated loss of over 15 million human lives globally and continues to have negative social, and economic implications worldwide. Vaccine platforms that can be quickly updated to counter newly emerging SARS-CoV-2 variants are critical in combating the COVID-19 pandemic. Messenger RNA-based SARS-CoV-2 vaccines can be easily updated and have shown superior efficacy over other vaccine types, yet their high cost, reactogenicity, and stringent need for ultracold storage limit their accessibility. Global access to economic, safe, and effective SARS-CoV-2 vaccines is a critical step toward reducing COVID-19-associated mortality and ending the pandemic. Several protein-based SARS-CoV-2 vaccines targeting the spike protein (or its receptor-binding domain) have demonstrated safety and efficacy in clinical studies. Moreover, protein-based vaccines can be updated to immunize against new virus variants. Protein-based vaccines do not contain live viruses and are safe to use in immunocompromised and elderly populations, and can be optimized to improve the immune outcome in these poorly immunoresponsive individuals by using adjuvants. SARS-CoV-2 shows high genetic variability, similar to other RNA viruses, and protein-based vaccines are an economically feasible vaccine platform that can be used to design new vaccines with durable protective immunity, in addition to expanding the vaccine coverage.

T-cell immunity to SARS-CoV-2: what if the known best is not the optimal course for the long run? Adapting to evolving targets

Humanity did surprisingly well so far, considering how unprepared it was to respond to the coronavirus disease 2019 (COVID-19) threat. By blending old and ingenious new technology in the context of the accumulated knowledge on other human coronaviruses, several vaccine candidates were produced and tested in clinical trials in record time. Today, five vaccines account for the bulk of the more than 13 billion doses administered worldwide. The ability to elicit biding and neutralizing antibodies most often against the spike protein is a major component of the protection conferred by immunization but alone it is not enough to limit virus transmission. Thus, the surge in numbers of infected individuals by newer variants of concern (VOCs) was not accompanied by a proportional increase in severe disease and death rate. This is likely due to antiviral T-cell responses, whose evasion is more difficult to achieve. The present review helps navigating the very large literature on T cell immunity induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and vaccination. We examine the successes and shortcomings of the vaccinal protection in the light of the emergence of VOCs with breakthrough potential. SARS-CoV-2 and human beings will likely coexist for a long while: it will be necessary to update existing vaccines to improve T-cell responses and attain better protection against COVID-19.

Efficacy and Safety of a Protein-Based SARS-CoV-2 Vaccine: A Randomized Clinical Trial

Importance

The protein-based SARS-CoV-2 vaccines FINLAY-FR-2 (Soberana 02) and FINLAY-FR-1A (Soberana Plus) showed good safety and immunogenicity in phase 1 and 2 trials, but the clinical efficacy of the vaccine remains unknown.

Objective

To evaluate the efficacy and safety of a 2-dose regimen of FINLAY-FR-2 (cohort 1) and a 3-dose regimen of FINLAY-FR-2 with FINLAY-FR-1A (cohort 2) in Iranian adults.

Design, Setting, and Participants

A multicenter, randomized, double-blind, placebo-controlled, phase 3 trial was conducted at 6 cities in cohort 1 and 2 cities in cohort 2. Participants included individuals aged 18 to 80 years without uncontrolled comorbidities, coagulation disorders, pregnancy or breastfeeding, recent immunoglobulin or immunosuppressive therapy, and clinical presentation or laboratory-confirmed COVID-19 on enrollment. The study was conducted from April 26 to September 25, 2021.

Interventions

In cohort 1, 2 doses of FINLAY-FR-2 (n = 13 857) or placebo (n = 3462) were administered 28 days apart. In cohort 2, 2 doses of FINLAY-FR-2 plus 1 dose of FINLAY-FR-1A (n = 4340) or 3 placebo doses (n = 1081) were administered 28 days apart. Vaccinations were administered via intramuscular injection.

Main Outcomes and Measures

The primary outcome was polymerase chain reaction-confirmed symptomatic COVID-19 infection at least 14 days after vaccination completion. Other outcomes were adverse events and severe COVID-19. Intention-to-treat analysis was performed.

Results

In cohort 1 a total 17 319 individuals received 2 doses and in cohort 2 5521 received 3 doses of the vaccine or placebo. Cohort 1 comprised 60.1% men in the vaccine group and 59.1% men in the placebo group; cohort 2 included 59.8% men in the vaccine group and 59.9% in the placebo group. The mean (SD) age was 39.3 (11.9) years in cohort 1 and 39.7 (12.0) years in cohort 2, with no significant difference between the vaccine and placebo groups. The median follow-up time in cohort 1 was 100 (IQR, 96-106) days and, in cohort 2, 142 (137-148) days. In cohort 1, 461 (3.2%) cases of COVID-19 occurred in the vaccine group and 221 (6.1%) in the placebo group (vaccine efficacy: 49.7%; 95% CI, 40.8%-57.3%) vs 75 (1.6%) and 51 (4.3%) in cohort 2 (vaccine efficacy: 64.9%; 95% CI, 49.7%-59.5%). The incidence of serious adverse events was lower than 0.1%, with no vaccine-related deaths.

Conclusions and Relevance

In this multicenter, randomized, double-blind, placebo-controlled, phase 3 trial of the efficacy and safety of FINLAY-FR-2 and FINLAY-FR-1A, 2 doses of FINLAY-FR-2 plus the third dose of FINLAY-FR-1A showed acceptable vaccine efficacy against symptomatic COVID-19 as well as COVID-19-related severe infections. Vaccination was generally safe and well tolerated. Therefore, Soberana may have utility as an option for mass vaccination of the population, especially in resource-limited settings, because of its storage condition and affordable price.

Trial Registration

isrctn.org Identifier: IRCT20210303050558N1.

Living with HIV and Getting Vaccinated: A Narrative Review

After 40 years of its appearance, human immunodeficiency virus (HIV) infection remains a leading public health challenge worldwide. Since the introduction of antiretroviral treatment (ART), HIV infection has become a chronic condition, and people living with HIV could have life expectancies close to those of the general population. People with HIV often have an increased risk of infection or experience more severe morbidity following exposure to vaccine-preventable diseases. Nowadays, several vaccines are available against bacteria and viruses. However, national and international vaccination guidelines for people with HIV are heterogeneous, and not every vaccine is included. For these reasons, we aimed to perform a narrative review about the vaccinations available for adults living with HIV, reporting the most updated studies performed for each vaccine among this population. We performed a comprehensive literature search through electronic databases (Pubmed-MEDLINE and Embase) and search engines (Google Scholar). We included English peer-reviewed publications (articles and reviews) on HIV and vaccination. Despite widespread use and guideline recommendations, few vaccine trials have been conducted in people with HIV. In addition, not all vaccines are recommended for people with HIV, especially for those with low CD4 cells count. Clinicians should carefully collect the history of vaccinations and patients' acceptance and preferences and regularly check the presence of antibodies for vaccine-preventable pathogens.

Development of SARS-CoV-2 Vaccine: Challenges and Prospects

The WHO declared coronavirus disease 2019 (COVID-19) a pandemic in March 2020, which was caused by novel coronavirus severe acute respiratory coronavirus 2 (SARS-CoV-2). SARS-CoV-2 made its first entry into the world in November 2019, and the first case was detected in Wuhan, China. Mutations in the SARS-CoV-2 genome distressed life in almost every discipline by the extended production of novel viral variants. In this article, authorized SARS-CoV-2 vaccines including mRNA vaccines, DNA vaccines, subunit vaccines, inactivated virus vaccines, viral vector vaccine, live attenuated virus vaccines and mix and match vaccines will be discussed based on their mechanism, administration, storage, stability, safety and efficacy. The information was collected from various journals via electronic searches including PubMed, Science Direct, Google Scholar and the WHO platform. This review article includes a brief summary on the pathophysiology, epidemiology, mutant variants and management strategies related to COVID-19. Due to the continuous production and unsatisfactory understanding of novel variants of SARS-CoV-2, it is important to design an effective vaccine along with long-lasting protection against variant strains by eliminating the gaps through practical and theoretical knowledge. Consequently, it is mandatory to update the literature through previous and ongoing trials of vaccines tested among various ethnicities and age groups to gain a better insight into management strategies and combat complications associated with upcoming novel variants of SARS-CoV-2.

Receptor-binding domain-based SARS-CoV-2 vaccine adjuvanted with cyclic di-adenosine monophosphate enhances humoral and cellular immunity in mice

Novel adjuvants are highly desired to improve immune responses of SARS-CoV-2 vaccines. This work reports the potential of the stimulator of interferon genes (STING) agonist adjuvant, the cyclic di-adenosine monophosphate (c-di-AMP), in a SARS-CoV-2 vaccine based on the receptor binding domain (RBD). Here, mice immunized with two doses of monomeric RBD adjuvanted with c-di-AMP intramuscularly were found to exhibit stronger immune responses compared to mice vaccinated with RBD adjuvanted with aluminum hydroxide (Al(OH)₃ ) or without adjuvant. After two immunizations, consistent enhancements in the magnitude of RBD-specific immunoglobulin G (IgG) antibody response were observed by RBD + c-di-AMP (mean: 15360) compared to RBD + Al(OH)₃ (mean: 3280) and RBD alone (n.d.). Analysis of IgG subtypes indicated a predominantly Th1-biased immune response (IgG2c, mean: 14480; IgG2b, mean: 1040, IgG1, mean: 470) in mice vaccinated with RBD + c-di-AMP compared to a Th2-biased response in those vaccinated with RBD + Al(OH)₃ (IgG2c, mean: 60; IgG2b: n.d.; IgG1, mean: 16660). In addition, the RBD + c-di-AMP group showed better neutralizing antibody responses as determined by pseudovirus neutralization assay and by plaque reduction neutralization assay with SARS-CoV-2 wild type. Moreover, the RBD + c-di-AMP vaccine promoted interferon-γ secretion of spleen cell cultures after RBD stimulation. Furthermore, evaluation of IgG-antibody titers in aged mice showed that di-AMP was able to improve RBD-immunogenicity at old age after 3 doses (mean: 4000). These data suggest that c-di-AMP improves immune responses of a SARS-CoV-2 vaccine based on RBD, and would be considered a promising option for future COVID-19 vaccines.

Safety and efficacy of the two doses conjugated protein-based SOBERANA-02 COVID-19 vaccine and of a heterologous three-dose combination with SOBERANA-Plus: a double-blind, randomised, placebo-controlled phase 3 clinical trial

Background

SOBERANA-02 is a COVID-19 conjugate vaccine (recombinant RBD conjugated to tetanus toxoid). Phases 1/2 clinical trials demonstrated high immunogenicity, promoting neutralising IgG and specific T-cell response. A third heterologous dose of SOBERANA-Plus (RBD-dimer) further increased neutralising antibodies. The aim of this study is to evaluate the safety and efficacy of two immunisation regimes: two doses of SOBERANA-02 and a heterologous three-dose combination with SOBERANA-Plus added to it.

Methods

From March 8th to June 24th, 2021 we conducted in Havana, Cuba a multicentre randomised, double-blind, placebo-controlled, phase-3 trial evaluating a two doses SOBERANA-02 scheme and a heterologous scheme with one dose SOBERANA-Plus added to it (RPCEC00000354). Participants 19-80 years were randomly assigned to receiving 28 days apart either the two or three dose scheme or placebo. The main endpoint was vaccine efficacy in preventing the occurrence of RT-PCR confirmed symptomatic COVID-19 at least 14 days after the second or third dose in the per-protocol population. We also assessed efficacy against severe disease and, in all participants receiving at least one vaccine/placebo dose, safety for 28 days after each dose.

Findings

We included 44,031 participants (52.0% female, 48.0% male; median age 50 years, range 19-80 years; 7.0% black, 24.0% mixed-race, 59.0% white) in a context of initial Beta VOC predominance, with this variant being partially replaced by Delta near the trial's end. Vaccine efficacy in the heterologous combination was 92.0% (95%CI 80.4-96.7) against symptomatic disease. There were no severe COVID-19 cases in the vaccine group against 6 in the placebo group. Two doses of SOBERANA-02 was 69.7% (95%CI 56.5-78.9) and 74.9% (95%CI 33.7-90.5) efficacious against symptomatic and severe COVID-19, respectively. The occurrence of serious and severe adverse events (AE) was very rare and equally distributed between placebo and vaccine groups. Solicited AEs were slightly more frequent in the vaccine group but predominantly local and mostly mild and transient.

Interpretation

Our results indicate that the straightforward to manufacture SOBERANA vaccines are efficacious in a context of Beta and Delta VOC circulation, have a favourable safety profile, and may represent an attractive option for use in COVID-19 vaccination programmes.

Funding

This study received funds from the National Fund for Science and Technology (FONCI-CITMA-Cuba, contract 2020-20) of the Ministry of Science, Technology and Environment of Cuba.

The Delta and Omicron Variants of SARS-CoV-2: What We Know So Far

The world has not yet completely overcome the fear of the havoc brought by SARS-CoV-2. The virus has undergone several mutations since its initial appearance in China in December 2019. Several variations (i.e., B.1.616.1 (Kappa variant), B.1.617.2 (Delta variant), B.1.617.3, and BA.2.75 (Omicron variant)) have emerged throughout the pandemic, altering the virus's capacity to spread, risk profile, and even symptoms. Humanity faces a serious threat as long as the virus keeps adapting and changing its fundamental function to evade the immune system. The Delta variant has two escape alterations, E484Q and L452R, as well as other mutations; the most notable of these is P681R, which is expected to boost infectivity, whereas the Omicron has about 60 mutations with certain deletions and insertions. The Delta variant is 40-60% more contagious in comparison to the Alpha variant. Additionally, the AY.1 lineage, also known as the "Delta plus" variant, surfaced as a result of a mutation in the Delta variant, which was one of the causes of the life-threatening second wave of coronavirus disease 2019 (COVID-19). Nevertheless, the recent Omicron variants represent a reminder that the COVID-19 epidemic is far from ending. The wave has sparked a fervor of investigation on why the variant initially appeared to propagate so much more rapidly than the other three variants of concerns (VOCs), whether it is more threatening in those other ways, and how its type of mutations, which induce minor changes in its proteins, can wreck trouble. This review sheds light on the pathogenicity, mutations, treatments, and impact on the vaccine efficacy of the Delta and Omicron variants of SARS-CoV-2.