Pharmaceutical groups Pfizer-BioNTech and Moderna have released trial data showing their Covid-19 vaccines to be about 95 percent effective at preventing the illness, while a rival company, AstraZeneca, this week said its vaccine could be up to 90 percent effective. So what happens next?
If regulators approve any of the vaccines in the coming weeks, the companies have said distribution could begin almost immediately, with governments around the world to decide who gets the treatment, and in what order. Here is an outline of the process:
When will companies roll out a vaccine?
Pfizer, Moderna and AstraZeneca have already started manufacturing their vaccines. Pfizer says it will have enough to inoculate 25 million people, Moderna enough for 10 million more, and AstraZeneca enough for a further 100 million.
The US Department of Defense and the Centers for Disease Control and Prevention (CDC) will manage distribution in the United States, probably starting in mid-December with an initial release of 6.4 million doses nationwide.
UK health authorities plan to roll out an approved vaccine as quickly as possible, also expected in December. In the European Union, it is up to each country in the 27-member bloc to start distributing vaccines to their populations.
Who will get a vaccine, and when, in the US?
Upon authorisation from the US Food and Drug Administration, the CDC has said first in line for vaccinations would be about 21 million healthcare workers and 3 million residents in long-term care facilities.
Essential workers, an estimated 87 million people who do crucial work in jobs that cannot be done from home, are the probable next group. They includes firefighters, police, and those working in schools, transportation, agriculture and food services.
Around 100 million adults with high-risk medical conditions and 53 million over the age of 65, considered at higher risk of severe illness, are the next priority.
US public health officials have said vaccines will be generally available to most Americans in pharmacies, clinics and doctors' offices starting in April so that anyone who wants a shot can have one by the end of June.
It remains unclear when a vaccine will be available for children. Pfizer and BioNTech have started testing their vaccine on volunteers as young as 12.
When will a vaccine be available in other countries?
Here in France, the pharmaceutical subcontracting laboratory Recipharm has been chosen by Moderna to produce part of its vaccine against Covid-19.
Recipharm has signed a letter of intent to produce the vaccine in France at its site in Monts, in the Indre-et-Loire department. The agreement is due to be finalised in December.
In his televised address on Tuesday evening, French President Emmanuel Macron emphasised that vaccination against Covid-19 will not be obligatory.
The European Union, the United Kingdom, Japan, Canada and Australia are all running rapid vaccine regulatory processes.
Many of AstraZeneca's doses this year are expected to go to the United Kingdom, where health officials have said that, if the vaccine is approved, they could begin vaccinating people in December. Priority will be given to people living and working in care homes.
In Europe, the EU drugs regulator has said it could rule on the safety of a Covid-19 vaccine in December. Most EU countries have said the first vaccines will go to the elderly and vulnerable and frontline workers like doctors.
Countries say they are buying vaccines via the European Commission's joint procurement scheme, which has negotiated deals for six different vaccines and nearly 2 billion doses.
However, delivery timelines vary and most countries are still drawing up plans for distributing and administering shots.
Italy expects to receive the first deliveries of the Pfizer-BioNTech treatment and AstraZeneca's product early next year. Spain plans to begin vaccination in January.
Germany, home to BioNTech, expects to roll out shots in early 2021 with mass vaccination centers in exhibition halls, airport terminals and concert venues. It will also use mobile teams for care homes. Front-line healthcare workers and other people at risk are expected to be among the first to be inoculated.
When will developing countries get a vaccine?
Covax, a programme led by the World Health Organization and the Gavi vaccine group to pool funds from wealthier countries and nonprofit organisations to buy and distribute vaccines to dozens of poorer countries, has raised nearly two billion euros.
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Its first goal is to vaccinate 3 percent of the people in these countries with a final goal of reaching 20 percent. It has signed a provisional agreement to buy AstraZeneca's vaccine, which does not require storage in specialised ultra-cold equipment like the Pfizer vaccine.
It is expected but not certain that less wealthy countries in Africa and South East Asia, such as India, will receive vaccines at low or no cost under this programme in 2021. Other countries such as those in Latin America may buy vaccines through Covax. Several are also striking supply deals directly with drugmakers.
How much will it cost?
Vaccine makers and governments have negotiated varying prices, not all of which have been made public. Prices range from a few euros for the AstraZeneca product, up to 40 euros for the two-dose Pfizer regimen. Many governments have said they will cover the cost of inoculating their residents.