Since the onset of the novel coronavirus in early 2020, China is researching five vaccine development technologies including inactivated vaccines, recombinant subunit vaccines, recombinant adenovirus vector vaccines, vaccines using attenuated influenza viruses as a vector, and mRNA and DNA-based nucleic acid vaccines.
David O’Connor, professor of pathology and laboratory medicine at the University of Wisconsin-Madison, said that the titer of neutralizing antibodies required for protection is not known. If two vaccines both exceed this threshold by a large margin, it does not matter which one has the greatest titer, which is the amount of antibodies to a disease found in a blood sample which show immunity to that disease.
“Other considerations such as ease of production, cost, lack of side effects, and frequency of delivery might be more important if two vaccines are equally protective,” he told NewsChina. “This is why multiple candidates are moving forward simultaneously.”
Chen Zhiwei, director of the AIDS Institute at the University of Hong Kong, is leading a research team on DNA-based nucleic acid vaccine development. He told our reporter that as an innovative technology, nucleic acid vaccines for humans have never been approved and are not ready for commercial use. It is anybody’s guess whether they will meet the needs of millions of people. He added that if the bottleneck is unblocked, a nucleic acid vaccine might be a good option to lead Covid-19 vaccine development because of its advantages, such as faster protection and lack of pre-existing immunity.
Yu said there are difficulties in developing mRNA vaccines. Even leading manufacturer Moderna has no experience of mass production of an mRNA coronavirus vaccine, as it is a completely new type of vaccine that has not so far been licensed for production for use against an infectious disease. China does not have intellectual property rights in mRNA vaccine development or the capacity for mass production.
Unlike DNA-based vaccines, mRNA, a messenger RNA molecule in cells that carries codes from DNA to make proteins, is unstable and there are many problems in its preservation and transportation. It works by “tricking” the body by introducing a synthetic version of the virus proteins into a cell, which provoke the body to create some of the virus’s molecules. So far, research on mRNA treatments has focused on cancers. Some scientists believe that an mRNA-based vaccine will be quicker to produce, easier to scale-up and more effective than traditional vaccines which are based on inactive doses, but there are still a lot of unknowns as the technique is new and untested.
US pharmaceutical giant Pfizer has to preserve its mRNA vaccine candidate at a temperature under -70 C, but Moderna’s vaccine candidate can be stored under -20 C.
Melanie Saville, director of vaccine development at the global partnership Coalition for Epidemic Preparedness Innovations (CEPI), has pointed out that storing a vaccine at -70 C or -4 C means very different things. It would add an enormous amount of complexity to build a -70 C requirement into a cold chain, Saville said in an article published on the CEPI website.
Besides the manufacturing, scalability and delivery, another consideration is one dose versus two doses. She added that the ideal would be a one-dose vaccine because it is easier and far less expensive.
“In low-income and middle-income countries, a single-dose campaign is likely to be more successful than a two-dose regimen. We’ve identified that’s a gap in our portfolio and we want to prioritize a single-dose regimen as one of our priorities,” she wrote.
According to the China National Biotec Group, a subsidiary of the China National Pharmaceutical Group (Sinopharm), an inactivated Covid-19 vaccine is most likely to be approved first in China. An inactivated vaccine uses a killed version of the germ that causes a disease to trigger an immune response. The company expects the two inactivated Covid-19 vaccines in development to hit the market in late 2020 or early 2021.
“Considering the production cost and potential security risks, the ones that move the fastest are probably not the best. They are only alternatives before the approval of other vaccines,” Qin Yuan, a vaccine development expert, told NewsChina.