Available Effective Vaccines in Preventing COVID-19: A Narrative Review

With the onset of the emerging coronavirus disease-2019 (COVID-19) in late December 2019 in China and its rapid spread around the world, scientists began research to develop and produce an effective vaccine. COVID-19 is caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). One of the most important structural features of this coronavirus is the presence of spike protein on its surface. This spike protein has been considered by many scientists as a suitable target for the development of vaccines against COVID-19. The SARS-CoV-2 spike protein binds directly to the ACE2 receptor on the surface of human alveolar epithelial cells (AECs), which facilitates virus entry and replication. By August 2021, more than 150 vaccines are developing in various stages of research and clinical trials to combat the pandemic. Most of these vaccines are based on attenuated infectious agent or mRNA, which can induce cellular and humoral immune systems to make antibodies to reduce the risk of death and severe complications when exposed to SARS-CoV-2. With the introduction of the first effective vaccine against COVID-19 by an American-German company called Pfizer–BioNTech on December, 2020, nine months after the first case of COVID-19, scientists were able to complete the multi-year process of producing a new vaccine in less than 10 months and the hopes for saving human beings and returning to normal life came alive. Other reputable companies around the world have since introduced the vaccine, including Moderna, Johnson & Johnson, Oxford/AstraZeneca, Sputnik V, Covaxin, Novavax, Sinovac, and Sinopharm. However, most of these vaccines have not received final approval from reputable organizations such as the FDA and WHO. Iran has also made efforts to develop and produce vaccines in this regard. With the introduction of these vaccines, by August 11, 2021, about 4.4 billion doses of vaccine have been injected worldwide, and global vaccination continues. Leading countries in vaccination include China, India, the United States, Brazil, and Japan, respectively. The major challenge facing existing vaccines is the variety of SARS-CoV-2 mutations that lead to the development of new strains that may be resistant to the vaccine. Therefore, scientific efforts to develop and upgrade vaccines continue.