With hundreds of thousands dying around the world, the race is on to find a vaccine to end the coronavirus pandemic.
More than 100 groups across the world are attempting to develop a vaccine, which is likely to induce longer lasting immunity than infection.
As scientists now worry that as restrictions are lifted the number of coronavirus cases will quickly rise, they know the best way to combat Covid-19 will be producing a vaccine.
But there is a potentially deadly risk that comes with this solution - and a "risk/benefit ratio" must be made by those in charge.
AstraZeneca, the Cambridge-based pharmaceutical group, is teaming up with Oxford University to manufacture and distribute a potential vaccine if clinical trials are positive.
They are already mass producing a possible vaccine on an industrial scale, before animal and human trials indicate whether it can lead to serious immune systems complications.
Michael Mosley was given access to the top-security Porton Down laboratory where vaccines from two of our top universities are being tested.
Researchers there are looking at vaccines produced by Oxford University and Imperial College London - and 30 million doses of Oxford’s vaccine could be ready for the UK as early as September.
Around 1,110 people will take part in its trial, half receiving the vaccine and the other half receiving a meningitis vaccine, and results are expected to begin to emerge next month.
They have stopped trials on some of the world's most dangerous diseases, anthrax, ebola and the plague, to divert all their attention and capability to coronavirus.
Professor Miles Carroll, deputy director of the National Infection Service at Public Health England, warns that a balance must be met.
He said: "Someone dying of cancer, you would risk giving them a more toxic drug to save their life.
"But if you’re vaccinating a healthy individual you need to have something that is extremely safe and would do no harm."
The vaccines are being tested on meerkats and ferrets, which will have their lungs checked for possible damage and are then challenged to see if the if has affected their functions.
The team will check that the vaccine doesn’t lead to rare immune systems complications that can cause serious disease after exposure to virus.
Dr Sandy Douglas, of the Jenner Institute at Oxford University, revealed it would normally take several years to have a vaccine considered for widespread use.
But due to the global pandemic, a vaccine may be fast-tracked to use as early as September, with mass production starting before confirmation it even works.
He explained: "We started moving to doing really clinical manufacturing at an industrial scale very early.
"We want the vaccine to be ready as soon as the clinical trial shows the vaccine can be safe and work on people.
"To have the vaccine ready then we need to start months and months in advance. We're hoping if everything goes really well we might have some vaccine ready to use in perhaps the early autumn."
Regulators might grant the emergency use of a vaccine to allow human trial to scale up to tens of thousands of people- with the vulnerable and key workers coming first.
Dr Douglas added: "It would initially be very restricted. Health care workers, maybe people living in care homes, perhaps older people with underlying lung dieases.
"The people with the most to benefit form the vaccine would be the most likely to receive it."
Because it's a modern virus, scientists have no idea of the long-term impact on the immune system so have been looking to studies done more than 30 years ago.
The Common Cold Unit was set up in Salisbury after the war to find treatment and vaccines for common respiratory infections - and in the 1960s identified coronavirus as a cause of the cold.
While those volunteers infected with rhinoviruses, which cause half of all colds, were immune a year later, the results were very different for coronavirus.
The coronavirus volunteers had virus in their nose when infected again a year later, which suggest that could pass it on without knowing.
Professor Wendy Barkley, a former researcher in the late 80s, explained that early evidence on today's coronavirus shows it doesn't necessarily provoke a strong immune response but can vary from person to person.
Professor Barkley said: "My suspicion is this group of viruses, the coronavirus in general, have in their armament a way of interfering with the way the immune response would normally work.
"So the antibodies get made more slowly than usual, perhaps fewer antibodies than usual and don’t get maintained for a long as we’d usually see with another virus."
The idea behind 'herd immunity' is that if enough of the population are infected and become immune to the virus then it could fade away.
However, the current evidence seems to show that not enough people will ever produce enough antibodies for this to work.
Professor Barkley added: "We can never achieve that high level where enough people at once have the antibodies that would mean the virus would be stuck and have nowhere to go."
Boris Johnson announced that the government will start easing lockdown measures when the reproductive number, how many individuals one person will go onto infect on average, starts to decrease.
This coronavirus has a basic reproductive number, or R value, of around 2.6 with no preventative measures in place.
Because people are infectious for a fairly short period of time, there is growing concern that even mass testing around 500,000 people a day will barely have an impact.
Dr Rosalind Eggo is part of a team of modellers at the London School of Hygiene and Tropical medicine that have used data from pre-lockdown contact patterns of 40,000 people to create a model.
This model, which is helping to inform government policy, tests the impact different measures may have on the R number.
Dr Eggo explained that mass testing would be logistically difficult and a lot depends on the behaviour of people who test positive for Covid-19.
She said: "First of all that's a lot of tests and a lot of people.
"It depends on the behaviour of people after they get a positive test whether they decrease their contact."
The model assumes that 10% of people won't self-isolate and is also based on completing 460,000 test a day, which is many more than is currently being carried out in the UK.
Dr Eggo added: "We think that people are infectious for a fairly short period of time so they will only test positive for a short time.
"It doesn’t have as much of an impact on the reproductive number as we might hope. It may change it from 2.6 to 2.5."
However, a possible solution being trialled on the Isle of Wight is digital contact tracing, which has been widely used in other countries to track the spread.
South Korea quickly brought R to near zero breaking circuit of transmission, but it works best when the rate is low, which is not the case in the UK right now.
Dr Eggo explained that if those people who are alerted decrease their contact and quarantine at home then that might decrease the R number to as low as 1.4.
While a combined strategy of digital contact tracing, manual contact tracing and decreasing the number of people you see outside work to just four brings the reproduction number to 0.9 in this particular model.
Horizon's second coronavirus special, which aired six weeks after the first part, was highly praised by viewers for giving clear and concise information on the pandemic.
One fan tweeted: "This #Horizon episode is fascinating. Linking changing use of land and deforestation due to global population doubling since 1970s - bringing humans and animal populations into contact - with the growth of potential pandemics. Hotspots in world for potential wildlife monitoring"
"Tonights episode of #Horizon should be made mandatory viewing. Calm explanations about the science (and what science is), and what we still need to learn," added another.
A third agreed: "I highly recommend watching yesterday's #Horizon episode on @BBC2 Coronavirus Special - part 2. Good and clear analysis and factual information on #COVID19 and also very interesting," added a third.
*Coronavirus: A Horizon Special is available on BBC iPlayer
