We are on the cusp of discovering whether we have a vaccine that works against coronavirus.
Scientists had to start from scratch earlier this year, but now the results of major trials are expected in the coming weeks or months.
Just to get to this point has been a remarkable and unprecedented feat, and data will arrive soon which will define our lives for years.
Why do we need a vaccine?
If you want your life to get back to normal then we need a vaccine.
Even now, the vast majority of people are still vulnerable to a coronavirus infection. It is only the restrictions on our lives that are preventing more people from dying.
But vaccines safely teach our bodies to fight the infection. This can either stop us catching coronavirus in the first place or at least make Covid less deadly.
The vaccine, alongside better treatments, is "the" exit strategy.
What do we know so far?
Trials have shown that experimental vaccines can train the immune system. Small studies have shown they can teach the body to make both antibodies, which prevent Covid from invading the body's cells, and T-cells, which kill infected cells.
However, the biggest question of all – "Is this enough to protect me?" – remains unanswered.
There are now 11 vaccines in the final stage of testing, However, this is also the crucial point where some experimental vaccines fail.
Some of the studies have recruited all of their volunteers and we are just waiting for the results.
The leading contenders are:
It is worth noting that four coronaviruses already circulate in human beings. They cause common cold symptoms and we don't have vaccines for any of them.
So when will we have a coronavirus vaccine?
There is widespread expectation that the first clinical trials will release their results this year.
This, by historical standards, is phenomenal. It would normally take years, if not decades, to develop a vaccine.
Exactly who will be immunised first will depend on where Covid is spreading when the vaccine becomes available and in which groups it is most effective.
The UK has not decided, for example, how to prioritise health and care workers who work with the most vulnerable people, relative to those most at risk if they catch the disease.
In broad terms, the over-80s, care home residents and health or care workers will be near the top of the list.
Age is, by far, the biggest risk factor for Covid, so the older you are, the sooner you are likely to be vaccinated.
Plans could change dramatically if the experimental vaccines are unsuitable or ineffective in the elderly.
Most experts think the vaccine will not be widely available until the middle of 2021.
Are there different types of vaccine?
The point of a vaccine is to harmlessly show parts of the virus to the immune system so it is recognised as an invader and learns how to fight it.
However, there are many ways to do this and researchers are using different approaches.
Both the Pfizer and Moderna vaccines inject pieces of the coronavirus' genetic code. Once inside the body, this starts making viral proteins to train the body. This is a completely new technique.
The Oxford and Russian vaccines take a harmless virus that infects chimpanzees and genetically modify it to resemble coronavirus, in the hope of getting a response.
Two of the big China-made vaccines use the original virus but in a disabled form, so so it cannot cause an infection.
Understanding which method produces the best results will be vital. Challenge trials, in which people are deliberately infected, could help answer these questions.
What still needs to be done?How many people need to be vaccinated?
It is hard to know without knowing how effective the vaccine is going to be.
It is thought that 60-70% of the global population need to be immune to the virus in order to stop it spreading easily (known as herd immunity) – in other words, billions of people, even if the vaccine works perfectly.
Would a vaccine protect everyone?
Not everyone responds the same to immunisation.
People will be watching the results in older people closely because they are most at risk from the virus.
But history also suggests any vaccine could be less successful in old people because an aged immune system does not respond as well to immunisation. We see this every year with the annual flu jab.
It may be possible to overcome this by either giving multiple doses or giving it alongside a chemical (called an adjuvant) that gives the immune system a boost.