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The UK government has three agreements in place to buy millions of doses of three yet-to-be-proven vaccines as countries scramble to find ways to immunise its population against coronavirus.

It has announced it has secured an agreement for 30 million doses of a Covid-19 vaccine by BioNTech and Pfizer, and also an in-principle deal for 60 million doses for antibody treatment by Valneva.

These figures are in addition to the 100 million doses of a vaccine that are being developed by Oxford University, in partnership with AstraZeneca, as well as another at Imperial College London.

Kate Bingham, chair of the government’s vaccine taskforce, said “optimistically” a vaccine could be available before the end of the year, however she warned it could take longer.

Speaking to BBC’s Radio 4 on Monday, she said: “I still think, optimistically, yes, we’ll be vaccinating by the end of the year.”

Later on Monday Boris Johnson downplayed hopes a Covid-19 vaccine will be developed in the near future, saying he could not be “100% confident” that a vaccine will be available this year or next.

The prime minister told Sky News: “Obviously I’m hopeful, I’ve got my fingers crossed, but to say that I’m 100% confident that we will get a vaccine this year – or indeed next year – is, alas, just an exaggeration. We are not there yet.

“It may be that the vaccine is going to come bounding over the hill like the cavalry, but we just can’t count on it.”

More than 150 vaccines are currently under development across the world, according to the World Health Organisation (WHO). Some 23 vaccines are in human trials.

So what are the details of the three vaccine programmes the UK government is pinning its hopes on?

Oxford University/AstraZeneca

The government has already ordered 100 million doses of the vaccine – called ChAdOx1 nCoV-19 – developed by Oxford University and pharmaceutical giant AstraZeneca.

The vaccine, made from a genetically engineered virus, is said to be one of the world’s “frontrunners” in the race and is currently in a combined phase 2/3 trial in the UK.

On Monday findings from the first phases of the study showed “promising” results although scientists warned it is too soon to know and larger trials are under way.

The early-stage trial, which involved 1,077 people, showed the vaccine is “safe, causes few side effects, and induces strong immune responses”, results published in The Lancet said.

There were no dangerous side-effects from taking the vaccine, however some people developed a fever or headache that researchers said could be managed with paracetamol. 

Over 4,000 participants have been enrolled into the clinical trial, with an addition 10,000 adult volunteers planned for the next stage of trials in the UK.

It has recently gone into phase 3 trials in South Africa and Brazil, where 5,000 volunteers received a trial vaccine on June 20 in Sao Paulo, Rio de Janeiro and a site in the northeast of Brazil.

The vaccine was developed at the University of Oxford’s Oxford Jenner Institute and is made from a genetically engineered virus that causes the common cold in chimpanzees. It is based on earlier work to produce a treatment for MERS (Middle East respiratory syndrome-related coronavirus). 

The chimpanzee virus is modified and engineered to express the coronavirus spike protein so it “looks” more like coronavirus to trigger a strong immune response in the human body.

Although the results so far for ChAdOx1 nCoV-19 look encouraging, there has been no indication yet whether the vaccine can prevent people from catching Covid-19 or even lesson their symptoms.

Campaigners warned last week that AstraZeneca could price poorer countries out of a British coronavirus vaccine in the future, due to a loophole in the non-profit agreement it signed with Oxford University.

BioNtech/Pfizer

The government has ordered 30 million doses of BNT162, a messenger RNA vaccine developed by German biotech firm BioNTech and the US pharmaceutical giant, Pfizer.

The vaccine is currently being tested in early to mid stage trials. If successful, the firms aim to make up to 100 million doses by the end of the year and potentially more than 1.2 billion doses by the end of 2021. 

Results from an early study, also announced on Monday, showed the vaccine was safe and induced an immune response in patients.

A trial testing 60 healthy adults in Germany showed the vaccine triggered virus-neutralising antibodies, echoing earlier results from a test in the US. 

The findings also showed an induction of a high level of T-cell responses against coronavirus. 

The vaccine uses the so-called messenger RNA approach, which spurs the body to create specific proteins with its own cells.

It is designed to train the immune system to produce antibodies to recognise and block the spike protein that the virus uses to enter and infect human cells.

In order to be successful, BNT162 will need to make T-cells that can recognise and kill infected cells as well as to generate antibodies to block other viral proteins. Nearly all effective vaccines induce an antibody and a T-cell response. 

Valneva 

The UK government has ordered a deal in principle for 60 million doses of the Valneva vaccine VLA2001, with an option of 40 million more doses if it proves to be safe and effective.

The vaccine is currently in pre-clinical stage and is expected to enter clinical trials by the end of the year and potentially reach regulatory approval in the second half of 2021. 

VLA2001 uses a more traditional method of vaccine development, by taking the whole coronavirus, inactivating it and then injecting it.

It has already previously been approved for active immunisation for the prevention of Japanese encephalitis.

“We’re taking an approach that already works, using tried and tested older technologies,” David Lawrence, CFO of Valneva, told HuffPost UK. 

Unlike the previous two, Valneva is not in the lead of the coronavirus vaccine race, but the French company has agreed to manufacture the product at its facilities in Livingston, Scotland in return for the government contributing to the cost of UK clinical studies.

Why does it take so long to develop a vaccine?

One of the main obstacles to developing a vaccine is that scientists currently do not know what level of immunity people need to prevent infection.

If successful, any vaccine will need to be introduced very cautiously as normal full trials will not take place. Vaccines normally require years of testing, plus time to produce to scale.

Vaccines must follow higher safety standards than other drugs, because they are given to millions of healthy people.

There is also a huge difference between finding a vaccine and producing it. Growing a virus needs to be done in a very controlled manner, with each stage monitored carefully by a highly trained workforce.

When could I get a vaccine?

Even if a vaccine were to be developed before the end of the year, it would not become widely available for much longer.

Frontline health and social care workers will be prioritised as well as people considered most at risk from Covid-19 because of their age or medical conditions.

People from Black, Asian and minority ethnic groups could also be among the first to get the vaccine, according to the government.

Widespread vaccination for the public could be available next year at the earliest, with most experts saying it will likely become widely available by mid-2021.

Can I volunteer for trials?

The government is calling on members of the public to sign up for trials of vaccines through the NHS Covid-19 vaccine research registry website.

At least eight large scale vaccine trials are expected to take place across the country.