Researchers around the world are trying to develop safe and effective vaccines against SARS-CoV-2, the virus that causes COVID-19. Here's their progress so far.
There are over 50 clinical trials worldwide, testing potential vaccines, known as candidates, against COVID-19. None of the vaccine candidates have been approved.
The majority of vaccine candidates for COVID-19 are still in a pre-clinical phase. That means the candidate vaccines are being tested in animal experiments, for example, rather than with human patients.
When those tests are deemed successful, candidate vaccines can move into clinical trial phases. That's when they are tested with humans. There are three clinical trial phases for efficacy and safety before a vaccine can be approved for use by humans. The phases differ from each other, most significantly in their scale:
Some companies, such as BioNTech and Pfizer in Europe, and Sinovac in China, have tested their vaccine candidates in several trials in parallel. For example, they have tested the same vaccine but in different age groups, or with different dosages.
If clinical trials are successful, a company can formally apply to regulatory bodies to have their vaccine approved for use by the general public.
Three regulatory authorities are considered to be particularly important in this context: The Food and Drug Administration (FDA) in the US, the European Medicines Agency (EMA), and the Pharmaceuticals and Medical Device Agency in Japan.
When a vaccine is approved, it doesn't mean everybody can get it immediately.
First, the vaccine has to be produced on a mass scale. With COVID-19, manufacturers aim to produce billions of doses by the end of 2021.
Second, logistics experts have to ensure appropriate distribution of the vaccine, and society has to decide who gets the vaccine first.
Read more: Can a vaccine be given out fairly?
In the end, though, it will be up to each individual to decide. A survey of more than 13,000 people in 35 countries most affected by COVID-19 showed that the majority of people asked would choose to get vaccinated.
It can take several years to develop an effective and safe vaccine. On average, it takes between 10 and 12 years, but it can take longer. The search for a vaccine against HIV has been going since the early 1980s — and, so far, without success.
In the case of COVID-19, researchers are racing to shorten the time it usually takes because of the ongoing pandemic. Despite the pressure that that brings, vaccine developers, manufacturers and the World Health Organization (WHO) say there will be no compromises on safety.
Research teams are aiming to accelerate, or limit, the time it takes to get to approval during the pandemic to an average duration of 17 months.
However, that will only be the beginning. Once clinical trials are successfully completed, and a vaccine is approved and produced, researchers start phase IV, during which they observe the progress of vaccinated patients.
Researchers are pursuing ten different approaches for vaccines against COVID-19.
Most of the vaccine candidates use a protein-based subunit — so, instead of using a complete pathogenic virus, they are built on a small component of it, such as a protein found in its outer shell.
That protein is administered to patients in a high dose, with the aim of inducing a fast and strong reaction by the human immune system.
The hope is that the immune system will "remember" the protein and trigger a similar defense reaction if or when it comes into contact with the actual virus.
Vaccines against hepatitis B and HPV (human papillomavirus), for example, are based on this principle.
COVID-19 vaccine candidates using this method are being tested in phase I and II trials and have not yet been tested on a large scale in phase III clinical trials.
Only three approaches have made it to phase III. It seems the most promising for the time being are non-replicating viral vectors, inactivated or killed viruses, and a novel RNA approach.
At time of writing, there were well over 100 research teams worldwide, developing a COVID-19 vaccine. So far, 10 teams have advanced their candidate vaccines to the third phase of clinical trials.
Five teams stand out for conducting the most extensive clinical trials:
Read more: COVID-19 vaccine: Who are the front runners?