Context: Recently, Two candidate vaccines for COVID-19 have entered the first phase of human clinical trials and another 60 candidate vaccines are in pre-clinical studies, the World Health Organisation (WHO) has confirmed.
Key Points

• A vaccine trial is a clinical trial that aims at establishing the safety and efficacy of a vaccine prior to it being licensed. 
• The vaccine candidate jointly developed by CanSino Biological Inc and Beijing Institute of Biotechnology uses the non-replicating viral vector as the platform, same as the non-corona candidates like Ebola, to develop a vaccine with a 'Adenovirus Type 5' candidate. 
• Adenoviruses are common viruses that cause pneumonia and can deliver potential antigens to stimulate the production of antibodies that work against the disease. 
• CanSino Biological Inc, in association with the Chinese Academy of Military Medical Science's Bioengineering Institute, had developed an Ebola vaccine in 2017. 
• The other vaccine that has entered the first phase of trials is from the US-based biotech firm Moderna and the National Institute of Allergy and Infectious Diseases (NIAID) combine. 
• This lipid nanoparticle (LNP) encapsulated mRNA candidate vaccine uses an RNA platform with multiple candidates. 
• In this, the virus's genetic information is de-coded from the DNA to make proteins. mRNA, or messenger RNA, acts as an intermediary between the genetic information in DNA and the amino acid sequence of proteins, which gives cells command to make proteins that fight the viruses. But such vaccines have not yet been approved for human use. 
• Normally, the vaccine candidate, from the pre-clinical stage, which includes testing in small and large animals, have to go through three phases of clinical trials to prove its safety and efficacy.
• These human trials are done on different population in various geographies and have to create huge data in the 3 phases of human trials for regulatory sanctions. 
• In emergencies like this, fast tracking is possible, but the vaccine candidates still have to go through various trials before being introduced in the market. Typically, only one in ten experimental vaccines make it all the way through to regulatory approval.