There are about 160 coronavirus vaccines in various stages of production as governments and pharmaceutical companies race to find a treatment for Covid-19.
It is hoped one of them will be a sterilising vaccine that can wipe out Covid -19, but it is also possible that none will be effective enough to go into production.
In the high-risk, high-cost world of drug development, it is also possible that a second generation of medicine will build on any success from the current race.
The rules for finding the vaccine are changing as testing processes that normally take years to complete are reduced to months.
Prof Lawrence Young, a virologist at Warwick University who specialises in how diseases can develop, explains the process of trials.
“There are five stages in producing and developing a vaccine – discovery research, pre-clinical, clinical development, regulatory review and manufacturing and delivery,” Prof Young said.
During discovery research, scientists try to understand how a virus behaves and the likely immune responses. This stage normally takes between two and five years.
When scientists have identified a potential vaccine and immune response, they move to the pre-clinical stage where they can help to find a type of vaccine to develop.
Prof Young said the medicine developed at the University of Oxford stitches the coronavirus model into a harmless virus that is good at delivering the vaccine.
“It uses the surface spike of protein but does not give you a heavy dose. The tried and tested approach is to ‘make the virus and inactivate it", or kill it.
The pre-clinical stage also uses animals and laboratory testing to help assess the drug's safety.
Clinical research is where all new medicine goes through three phases of testing.
“Phase 1 is about safety testing," Prof Young said.
"We take a small number of people, perhaps 10 or 15, and check a dose and make sure it does not have severe side effects.
“We are not looking at the different outcomes, just making sure it is safe in humans and whether we can identify a safe dose.
“Phase 2 is checking it has the right immune response. At the moment, we don’t know what an effective immune response is.
"Several hundred people take part in this phase. For the Oxford vaccine trial they had more than 1,000 people.
"Phase 3 assesses if the vaccine reduces the diseases and infection."
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A municipal worker wears a face mask and shield at the Bosa neighborhood, one of the areas with more Covid19 cases in Bogota, Colombia. AFP -
Medical workers carry a man who is the last patient recovered from the Covid19 coronavirus infection in the Wuhan, pulmonary hospital before he leaves the hospital in Wuhan, in China's central Hubei province. AFP -
A nurse changes the medications of a patient suffering from the coronavirus disease at the Intensive Care Unit of Emilio Ribas Institute in Sao Paulo, Brazil. Reuters -
A woman is disinfected at her request at the entrance of Cariacu, Ecuador. Every vehicle or person entering the community has to be disinfected in an attempt to curb the spread of the coronavirus. AP Photo -
An employee of the Mugda Medical College and Hospital collects a swab sample from a resident to test for the Covid19 coronavirus, in Dhaka, Bangladesh. AFP -
An official sprays disinfectant inside a school amid the ongoing coronavirus pandemic in Denpasar, Bali, Indonesia. EPA -
A man takes a customer's body temperature wearing a face mask before entering a shopping area, after the Colombian government decided to relax social restrictions amid the outbreak of the coronavirus disease, in Bogota, Colombia. Reuters -
Police officers wearing facemasks stand guard next to a street sealed by the authorities at I-8 residential sector in Islamabad as cases of COVID-19 coronavirus continue to rise in Pakistan. AFP -
An employee wearing a protective mask holds Mickey and Minnie Mouse shaped balloons at Walt Disney Co.'s Disneyland Resort in Hong Kong, China. Bloomberg -
A man wearing a mask to help curb the spread of the new coronavirus is reflected in the mirror of his motorcycle in Cariacu, Ecuador. AP Photo -
A sign that reads, "Mandatory to wear a mask on all the site", is seen at the entrance of the Eiffel Tower as she gets ready to re-open to the public following the coronavirus outbreak, in Paris, France. Reuters -
A man wearing a face mask rides the subway, following new cases of the coronavirus disease infections in Beijing, China. Reuters -
Doug Hassebroek pours confetti over his daughter Lydia, celebrating her graduation ceremony at their home during the outbreak of coronavirus disease in Brooklyn, New York, USA. Reuters -
Carol Reihart, a certified nursing assistant at Little Sisters of the Poor, and resident Kay Canyock wave to cars filled with family, friends, and volunteers during a parade to celebrate Canyock's 100th birthday and the birthday of fellow resident Mary Sahayda, who turned 103 on the same day, at Little Sisters of the Poor home for the elderly in Pittsburgh, Pennsylvania, USA. Pittsburgh Post-Gazette via AP -
Leonardo Da Vinci bookstore owner, Brazilian bookseller Daniel Louzada,packs a book for an online order placed on the bookstore's website, inaugurated during the pandemic since the store was closed to follow social distance measures to curb the spread of the new coronavirus in Rio de Janeiro, Brazil. AFP -
Michael Antonorsi, Chief Joy Activator at Chuao Chocolatier, sits in a hammock while working on a laptop from his beachfront home during the outbreak of the coronavirus in Leucadia, California, USA. Reuters -
A policeman stands guard along the empty famous white beach of Boracay Island in central Philippines, as community quarantine against Covid19 still continues throughout the country, with foreign tourists still banned on beaches. AFP -
A priest walks along a dusty path at the Martires 19 de Julio cemetery, on the outskirts of Lima, Peru as the death toll remains unabated in Peru's capital. AP Photo
Regulatory review is the final stage in the approval process, where data from all the human trials are assessed by national or international authorities.
In the UK, that is the Medicines and Healthcare Products Regulatory Agency. In the EU, it is the European Medicines Agency, and the US has the Food and Drug Administration.
Once approved, the final stage is manufacture and delivery, which can involve building new factories or labs to produce the drug in sufficient quantities to meet demand.
The pharmaceutical companies must also ensure there is a supply route to get it into hospitals and surgeries.
Why are things moving so fast with the coronavirus trials?
Normally, each stage of development can take years, but less than a year after the first coronavirus patient was identified, 160 vaccines are in development.
Most will not reach production.
Prof Young said an influx of government money, streamlined processes and parallel operations all helped to speed up the vaccine process.
Government money is helping to reduce the risks for the pharmaceutical companies.
Factories are being built on the hope that a drug will become approved as a successful vaccine, in a risk that normally would not be taken until after the drug is approved.
Prof Young said it was hoped that a sterilising vaccine would be found, which you would take it once and not need booster shots.
He said it was also possible that a second generation of drugs would be needed to achieve that goal.
Prof Young said that of the vaccines in development, four were in Phase 3, 12 in Phase 2, and 18 in Phase 1.
Prof Sarah Gilbert, who is leading the Oxford team, told the BBC's Today programme that it was too early to know if their vaccine could become a sterilising vaccine.
“We can only know that when the Phase 3 trials have got much further along, when we have a lot of people vaccinated, half with coronavirus vaccine and half with another vaccine, and we start to count the number of infections in those trials," Prof Gilbert said.
"And that’s very unpredictable. It depends on the cases that are happening in the areas where vaccinations are taking place.
"Case numbers have been going up and down in different countries, so it’s very hard to understand when we’ll get those results."
