The US government's 'Operation Warp Speed' initiative is reported to have identified its priority COVID-19 vaccines that will receive additional funding and support.
The operation was recently established by the US government with the goal of developing a vaccine against COVID-19 by the end of 2020.
The New York Times (NYT) has reported five companies have been selected - Moderna, Johnson & Johnson, Pfizer, MSD and AstraZeneca-Oxford. Bloomberg reported an additional two as yet unnamed companies could also be included.
The companies will receive direct US government support, including for clinical trials and manufacturing.
According to the NYT, Moderna, Johnson & Johnson and the AstraZeneca-Oxford vaccine efforts have already received a combined US$2.2 billion in US government support.
The vaccines are based on a range of technologies but all are being developed based on accelerated timelines - where different stages of the clinical trial program are conducted in parallel.
Moderna's mRNA-1273, which has just started a phase two trial before the publication of reviewed phase one trial results, is a gene-based vaccine. It could become the first RNA vaccine ever approved.
The AstraZeneca-Oxford vaccine is based on an adenovirus viral vector that is similar to the delivery system used in gene therapy.
The company has committed to manufacturing one billion doses in 2020 and 2021 with 400 million doses already committed to the US and UK.
It has also just announced a new US$750 million deal with the Coalition for Epidemic Preparedness Innovations (CEPI) and Gavi, the Vaccine Alliance, for 300 million doses by the end of 2020.
The new deal also includes a separate licensing agreement with the Serum Institute of India (SII). SII will supply an additional one billion doses of the vaccine for low and middle-income countries. This includes a commitment to provide 400 million before the end of 2020.
Johnson & Johnson is also developing a viral vector vaccine.
It expects human clinical studies to begin in September 2020 and it "anticipates" the first batches could be available for emergency use authorisation in early 2021.
Pfizer is developing its vaccine in collaboration with German company BioNtech. Its BNT162 vaccine is based on the gene-based RNA technology.
MSD is working on two potential vaccines.
It has partnered with the non-government research organisation IAVI on the development of a vaccine based on the recombinant vesicular stomatitis virus (rVSV) technology. The technology is used for MSD's Ebola Zaire virus vaccine, ERVEBO.
It has also announced the acquisition of Austrian company Themis Bioscience. The companies already had a partnership focussed on the development of vaccines using the measles virus vector platform.
Vaccines generally take several years to develop because they are tested in the community. The important measure of efficacy and a significant purpose of late-stage trials is exposure to the virus in the community over time. This follow-up has often lasted several years as companies build evidence of durable efficacy and safety.
Any COVID-19 vaccine distributed at large scale in 2020 or 2021 will effectively be investigational.
The director of the US National Institute of Allergy and Infectious Diseases, Dr Anthony Fauci, has expressed optimism over the accelerated development of a vaccine. Yet he has also consistently highlighted the need for caution given the time required to gather evidence of a vaccine's durability.