Over 90 vaccine candidates are being developed as part of the global response to the COVID-19 pandemic. A snapshot of the eight different ways to elicit host immunity with vaccines under development is given in a guide by Ewen Callaway in a recent Nature article. Candidates can take the form of inactivated virus, viral vectors, nucleic acid, protein/peptide based and virus like particles. Some have already entered phase I and others remain in the exploratory stage. There is also a concerted effort to form public-private partnerships to speed up the process.
Virus vaccines (Live attenuated or inactivated):At least seven teams are developing vaccines using the virus itself, in a weakened or inactivated form. Several existing vaccines are made this way, including those against measles and polio, but they require extensive safety testing. Sinovac Biotech in Beijing has initiated testing of an inactivated version of SARS-CoV-2 in humans.
Viral-vector vaccines (Replicating or non replicating): Nearly 25 groups are working on viral-vector vaccines. A virus such as measles or adenovirus is subjected to genetic engineering so that it can produce coronavirus proteins in the body. These viruses are weakened and cannot cause disease. There are two types – those that can still replicate within cells and those that cannot as the key genes have been disabled.
Nucleic-acid vaccines: Some 20 teams aim to use genetic instructions (in the form of DNA or RNA) for a coronavirus protein that incites an immune response. The nucleic acid is inserted into human cells, which then churns out copies of the virus protein; most of these vaccines encode the virus’s spike protein
Protein-based vaccines: Many researchers want to inject coronavirus proteins directly into the body. Fragments of proteins or protein shells that mimic the coronavirus’s outer coat can also be used (virus subunit or virus like particle).