In addition, they need to be kept awesome, and therefore a significant logistical mode of distribution is needed in order to provide a vaccine with high efficacy and without logistical challenges during distribution [61]. 6.2. to the interaction of the S protein with the angiotensin-converting enzyme 2 (ACE-2). Therefore, there are some concerns that need to be tackled and challenges concerning logistic problems, such as strict storage at low temps for some vaccines. With this review, we discuss the limits of vaccines developed against COVID-19 and possible innovative methods. Keywords: COVID-19, recombinant vaccines, pandemic, S protein, innovative methods 1. Introduction Large population density, improved contact with animal reservoirs, quick transport, and massive population motions represent the main determinants of the global distributing of growing pathogens with pandemic potential [1,2]. In particular, respiratory viruses are able to spread across wide geographical areas in a short period of time, causing high levels of morbidity and mortality. Among airborne pathogens, coronaviruses (CoV) have demonstrated the ability to cause threatening pandemic events [1,2]. Despite the recent emergence of several zoonotic pathogens highlighting the need for global preparedness and the quick development of vaccines against previously unfamiliar pathogens [3], at the beginning of the SARS-CoV-2 pandemic, there were still no vaccines against human 16-Dehydroprogesterone being coronaviruses; furthermore, those which have been successfully developed inside a few months time do not look like capable of ensuring universal, long-lasting safety [4,5]. In particular, the emergence of SARS-CoV-2 variants with decreased susceptibility to the neutralizing antibody reactions induced by currently available COVID-19 vaccines increases the possibility of breakthrough infections [6]. In addition, convalescent plasma from previously infected individuals does not reduce the risk of hospitalization due to COVID-19 [6]. Therefore, alternate or complementary methods need to be regarded as in order to develop vaccines able to induce a enduring immunological response and to favor the quick development and deployment of a high volume of vaccines for pandemic response. With this review, we discuss the advantages and the limits of currently available vaccines against COVID-19 and the main innovative approaches that might be used to tackle these bottlenecks. 2. Epidemiology The SARS-CoV-2 coronavirus belongs to a large family of enveloped, positive-sense single-stranded RNA viruses capable of infecting many varieties of parrots and mammals, including humans [7]. You will find hundreds of coronaviruses, most of which circulate among pigs, camels, bats, snakes, pangolins, and pet cats. Most human being coronaviruses cause nothing more than a common chilly [7]. Before the SARS-CoV-2 pandemic, two additional zoonotic coronaviruses have undergone varieties passage, causing several outbreaks: SARS-CoV, which emerged at the end of 2002 in China and was 16-Dehydroprogesterone recognized in Hong Kong in 2003 [8,9,10], and the Middle East Respiratory Syndrome coronavirus (MERS-CoV), which was recognized within the Arabian peninsula in 2012 [11]. The agent causing the current pandemic, SARS-CoV-2, emerged in late 2019 in China and quickly spread throughout the world [12]. As of 28 January 2022, a total of 364,191,494 instances of COVID-19 had been confirmed, including 5,631,457 deaths [13]. The original strain of Wuhan SARS-CoV-2, the cause of COVID-19, probably originated from bats and may become transmitted by asymptomatic, presymptomatic, and symptomatic individuals through close 16-Dehydroprogesterone contact via exposure to infected droplets and, to a lesser degree, aerosols [14,15]. This 1st strain was Rabbit Polyclonal to Cytochrome P450 26C1 followed by multiple variants resulting from genetic recombination within infected cells; among them, the Delta variant, formerly called B.1.617.2, and the Omicron variant, formerly called B.1.1.529, recently spread across the world as a result of their improved transmissibility and higher rates of presymptomatic and asymptomatic transmission [16,17]. Human being infection due to SARS-CoV-2 can be asymptomatic or cause symptoms that range in severity from slight common colds to essential respiratory illnesses such as acute respiratory stress syndrome and pneumonia [18]; several nonrespiratory symptoms, such as chest pain, abdominal pain, diarrhea, vomiting, cardiac arrhythmias, myalgias, arthralgias, general malaise, headache, and irritability, often complicate the medical picture of COVID-19 individuals [19]. Severe and acute symptoms, often associated with fatal results, appear more frequently in older individuals with comorbidities [18,20,21] and frailty [22,23]. 3. Genome Structure, Pathogenesis, and Viral Receptor Analysis SARS-CoV-2, belonging to the family and the genus [24], is characterized by a polycistronic RNA genome of 27.9 kb containing 14 open reading frames (ORFs), most of which are.