A potential Covid-19 vaccine entered final-stage clinical trials in the UAE to test the effectiveness of the jab in thousands of volunteers.
The vaccine was developed by Chinese state-owned manufacturer Sinopharm and is being tested on 5,000 volunteers in Abu Dhabi and 15,000 people could eventually be involved.
Sheikh Abdullah bin Mohammed Al Hamed, chairman of the Department of Health Abu Dhabi, was the first volunteer to receive the jab. Others have since joined the trial.
It is one of dozens of vaccines in development against Covid-19. But how does it work?
And when is a vaccine against the disease expected to be available to the public?
Here we explain:
The vaccine being trialled in Abu Dhabi is 'inactivated'. What does that mean?
It is one type of vaccine designed to protect people against the disease. It uses a “killed” version of the virus that causes the illness.
The downside is inactivated vaccines do not generally provide protection that is as strong as live-attenuated vaccines, which use a weakened form of the virus.
Because inactivated vaccines are less like the natural infections they are designed to prevent, several doses can be required to provide ongoing protection.
They can, however, be extremely effective. For example, cases of Meningitis B plummeted in the UK after the introduction of an inactivated vaccine, which protects against almost 90 per cent of strains of the disease.
Between 2015 and 2018, an estimated 277 out of an expected 446 cases of the disease were prevented because of the programme, according to health authorities in the UK.
How many Covid-19 vaccines are in there in development around the world?
More than 140 vaccines are at various stages of development. Only three are in phase 3 trials, which is the final stage before manufacturing.
They include the Sinopharm vaccine being tested in Abu Dhabi, which generated neutralising antibodies in 100 per cent of volunteers in the first two phases of the clinical trials, according to the manufacturer.
Researchers called the pursuit of neutralising antibodies the “holy grail” of viral vaccines.
But because Covid-19 is relatively new, researchers say it is not known whether neutralising antibodies will be enough to protect people from the disease, or whether another part of the immune system, such as T cells, will be important in clearing the infection.
The phase 3 trial of the Abu Dhabi vaccine will address this by testing whether it is effective in a large group of people.
How long do vaccines normally take to develop?
Years. A mumps vaccine was the fastest to be approved, but it took four years from the collection of viral samples to the licensing of the medicine in 1967.
Researchers are trying to speed up the process for a Covid-19 vaccine, but there are reasons to be cautious. Models showed that some preliminary vaccines against Sars, a cousin of the virus that causes Covid-19, enhanced the infection.
What is the approval process?
Vaccines have to successfully pass through three phases of clinical trials.
In the first phase, between 20 to 100 healthy volunteers receive the vaccine to determine whether it is safe or has any serious side effects, according to the US Centres for Disease Control and Prevention.
The number of recipients expands to “several hundred” in phase 2, which examines the most common short-term side effects and how volunteers’ immune systems react to the vaccine.
In phase 3, hundreds or thousands of volunteers receive the vaccine. This helps researchers determine how people who get it compare with those who do not.
The UAE was chosen for the phase 3 trial because of its diverse population, which comprises more than 200 nationalities. That will give researchers a glimpse into the effects of the vaccine on several ethnic groups.
What happens during a phase 3 trial?
Once the volunteers receive their vaccine, they will be asked to monitor their symptoms.
Officials behind the Abu Dhabi trial said anyone who received the vaccine would be closely monitored for up to year and asked to keep a "vaccine diary" to record any symptoms.
When is a vaccine against Covid-19 expected to be ready?
Experts expect a vaccine to be available by mid-2021, about 12 to 18 months after the virus was first detected.
But some say it could happen sooner.
Dr Anthony Fauci, a member of the US coronavirus task force, said a vaccine could be available at the end of 2020 or the start of 2021.