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COVID-19 is still a deadly disease that remains yet a major challenge for humans. In recent times, many large pharmaceutical and non-pharmaceutical companies have invested a lot of time and cost in fighting this disease. In this regard, today's scientific knowledge shows that designing and producing an effective vaccine is the best possible way to diminish the disease burden and dissemination or even eradicate the disease. Due to the urgent need, many vaccines are now available earlier than scheduled. New technologies have also helped to produce much more effective vaccines, although the potential side effects must be taken into account. Thus, in this review, the types of vaccines and vaccine designs made against COVID-19, the vaccination programs, as well as the delivery methods and molecules that have been used to deliver some vaccines that need a carrier will be described.

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Islet cell transplantation, as a treatment of type 1 diabetes, has a lot of complexity such as allograft rejections and an insufficient number of donors. The liver can be used as a replacement for endogenous insulin production. Hepatocytes can inherently respond to glucose levels and secrete proteins. Utilization of mesenchymal stem cells for curing diabetes represents a major focus of recent investigations. As a new choice for transplantation, we have proposed glucose‐regulated insulin‐producing hepatocyte‐like cells, which produce insulin dependent on glucose levels. We have transfected human Wharton's jelly mesenchymal stem cells with the special construct, which included homology arms and glucose‐responsive elements upstream of the minimum liver‐type pyruvate kinase promoter‐directed insulin gene. Then, we have differentiated these transfected cells to hepatocyte‐like cells by using serial exposure of different inducing material and exogenous growth factors. Immunofluorescence analyses have demonstrated the expression of albumin, cytokeratin‐18, Hep‐Par1, α‐fetoprotein, and insulin. The expression of hepatocyte marker genes in the differentiated cells was confirmed by reverse‐transcription polymerase chain reaction. Interestingly, flow cytometry results showed that approximately 60% of the insulin‐producing hepatocyte‐like cells were simultaneously cytochrome P450 3A4 (CYP3A4) and insulin positive. CYP3A4 is a significant enzyme found in mature liver tissue. This confirmed that the differentiation and the transfection procedures were done correctly. They were functionally active by releasing insulin in response to elevated glucose concentrations in vitro. These applicable cells could be used in the liver for cell therapy of diabetes.