Image copyright Reuters

Coronavirus still poses a significant threat, but there are no vaccines proven to protect the body against the disease it causes - Covid-19.

But by the end of the year, there could be at least half a dozen different coronavirus vaccines in clinical trials, including one being developed by University of Oxford that is already in an advanced stage of testing.

Why is a coronavirus vaccine important?

The virus spreads easily and the majority of the world's population is still vulnerable to it. A vaccine would provide some protection by training people's immune systems to fight the virus so they should not become sick.

This would allow lockdowns to be lifted more safely, and social distancing to be relaxed.

What sort of progress is being made?

Research is happening at breakneck speed. About 140 vaccines are in early development, and around two dozen are now being tested on people in clinical trials.

Trials of the Oxford vaccine show it can trigger an immune response, and a deal has been signed with AstraZeneca to supply 100 million doses in the UK alone.

The first human trial data back in May indicated the first eight patients taking part in a US study all produced antibodies that could neutralise the virus.

A group in China showed a vaccine was safe and led to protective antibodies being made. It is being made available to the Chinese military.

Other completely new approaches to vaccine development are in human trials.

However, no-one knows how effective any of these vaccines will be.

When will we have a coronavirus vaccine?

A vaccine would normally take years, if not decades, to develop. Researchers hope to achieve the same amount of work in only a few months.

Most experts think a vaccine is likely to become widely available by mid-2021, about 12-18 months after the new virus, known officially as Sars-CoV-2, first emerged.

That would be a huge scientific feat and there are no guarantees it will work.

Four coronaviruses already circulate in human beings. They cause common cold symptoms and we don't have vaccines for any of them.

What do I need to know about the coronavirus?

What still needs to be done?

Multiple research groups have designed potential vaccines, however, there is much more work to do.

Trials need to show the vaccine is safe. It would not be useful if it caused more problems than the disease

Clinical trials will also need to show vaccines provoke an immune response, which protect people from getting sick

A way of producing the vaccine on a huge scale must be developed for the billions of potential doses

Medicines regulators must approve it before it can be given

Finally there will be the huge logistical challenge of actually immunising most of the world's population

The success of lockdowns has made the process slower. To know if the vaccine works, you need people to actually be infected.

The idea of giving people the vaccine and then deliberately infecting them (known as a challenge study) would give quicker answers. The concern is that it is too dangerous and would not be ethical at this stage to carry them out - although some think it should not be off the table..

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 people needed to be immune to the virus in order to stop it spreading easily (known as herd immunity).

But that would be billions of people around the world even if the vaccine worked perfectly.

Media playback is unsupported on your device Media caption Epidemic v pandemic: What's the difference?

How do you create a vaccine?

Vaccines harmlessly show viruses or bacteria (or even small parts of them) to the immune system. The body's defences recognise them as an invader and learn how to fight them.

Then if the body is ever exposed for real, it already knows what to do.

The main method of vaccination for decades has been to use the original virus.

The measles, mumps and rubella (MMR) vaccine is made by using weakened viruses that cannot cause a full-blown infection. The seasonal flu jab takes the main strains of flu doing the rounds and completely disables them.

Some scientists, particularly those in China, are using this approach.

Image copyright Science Photo Library Image caption A Russian lab tests for infection with the Covid-19 coronavirus

There is also work on coronavirus vaccines using newer, and less tested, approaches called "plug and play" vaccines. Because we know the genetic code of the new coronavirus, Sars-CoV-2, we have the complete blueprint for building it.

The Oxford researchers have put small sections of its genetic code into a harmless virus that infects chimpanzees. They appear to have developed a safe virus that looks enough like the coronavirus to produce an immune response.

Other groups are using pieces of raw genetic code (either DNA or RNA depending on the approach) which, once injected into the body, should start producing bits of viral proteins which the immune system can learn to fight. However, this approach is completely new.

Would a vaccine protect people of all ages?

It will, almost inevitably, be less successful in older people, because aged immune systems do not respond as well to immunisation. We see this 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.

Who would get a vaccine?

If a vaccine is developed, then there will be a limited supply, at least initially, so it will be important to prioritise.

Healthcare workers who come into contact with Covid-19 patients would top the list. The disease is most deadly in older people so they would be a priority if the vaccine was effective in this age group.

The UK has also said other people considered to be at high risk - potentially included those with some conditions or from certain ethnicities - may be prioritised.

Follow James on Twitter