cure

As a young man, Stephen Crohn could only watch helplessly as one by one, his friends began dying from a disease which had no name. When his partner, a gymnast called Jerry Green, fell desperately ill in 1978 with what we now know as Aids, Crohn simply assumed he was next.

But instead as Green became blind and emaciated as the HIV virus ravaged his body, Crohn remained completely healthy. Over the following decade, dozens of friends and other partners would meet a similar fate.

In 1996, an immunologist called Bill Paxton, who worked at the Aaron Diamond Aids Research Center in New York, and had been looking for gay men who were apparently resistant to infection, discovered the reason why. When Paxton tried to infect Crohn's white blood cells with the HIV virus in a test tube, it proved impossible.

It transpired that Crohn had a genetic mutation – one which occurs in roughly 1% of the population – which prevents HIV from binding to the surface of his white blood cells. Over the following decade, scientists developed an anti-retroviral drug called maraviroc, which would transform the treatment of HIV by mimicking the effect of this mutation. It has proved crucial in helping to control the virus in infected people.

While Crohn died in 2013 at the age of 66, his story left a legacy that has stretched well beyond HIV. Over the past two decades, it has inspired a whole new realm of medical science, where scientists look to identify so-called "outliers" like Crohn, who are either unusually resilient or susceptible to disease, and use them as the basis for discovering new treatments.

Mass vaccination campaigns are under way in the fight back against the coronavirus.

A range of vaccines, designed in completely different ways, are being used to reduce people's chances of getting sick, needing hospital treatment or dying.

And two new vaccines have just been shown to work in large scale clinical trials.

Why do we need a vaccine?

It is more than a year since the virus first emerged, yet the vast majority of people are still vulnerable to the virus.

The restrictions on our lives are the only thing holding the virus in check as they reduce opportunities for the virus to spread.

Vaccines teach our bodies to fight the infection and are "the" exit strategy from the pandemic.

Comparing the Vaccines:

In short, any authorised vaccine offered to you is a good one to take.

In February, US regulators formally approved the single-shot Johnson & Johnson coronavirus vaccine - the latest to get the green light.

Unlike Pfizer and Moderna vaccines, which use new mRNA vaccine technology and require two shots, the Johnson & Johnson vaccine uses a common cold virus that has been engineered to make it harmless. It then safely carries part of the coronavirus's genetic code into the body. This is enough for the body to recognise the threat and then learn to fight coronavirus.

Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has said that all the vaccines available in the US were good vaccines, and stressed that the Johnson & Johnson jab is "not the weaker vaccine".

The concern comes down varying to efficacy data released from clinical trials - but those figures aren't all they appear to be, say experts.