LONDON (REUTERS) - Drugmakers and research centres around the world are working on Covid-19 vaccines, with large global trials of several of the candidates involving tens of thousands of participants well under way.

The following is what we know about the race to deliver vaccines to help end the coronavirus pandemic that has claimed more than 1.34 million lives worldwide:

Who is furthest along?

US drugmaker Pfizer Inc and German partner BioNTech released final late-stage trial data last Wednesday (Nov 18) that showed their shot was 95 per cent effective at stopping Covid-19, the highest efficacy rate so far.

The companies are the first to publish final Phase III efficacy and safety data and plan to apply for an emergency use authorisation (EUA) in the United States within days.

On Nov 16, another US pharmaceutical company, Moderna Inc, released interim data showing that its vaccine worked in a large, late-stage clinical trial with a 94.5 per cent efficacy rate.

Interim late-stage trial results for Russia's Sputnik V vaccine published on Nov 11 showed the shot is 92 per cent effective.

AstraZeneca said on Monday that its vaccine for the Covid-19, developed by Oxford University, could be around 90 per cent effective without any serious side effects.

Johnson & Johnson says it is on track to deliver data this year.

What happens in these trials?

The companies are testing their vaccines against a placebo - typically saline solution - in healthy volunteers to see if the rate of Covid-19 infection among those who got the vaccine is significantly lower than in those who received the dummy shot.

What were pharma companies waiting for to release data?

The trials rely on subjects becoming naturally infected with the coronavirus, so how long it takes to generate results largely depends on how pervasive the virus is where trials are being conducted.

Each drugmaker has targeted a specific number of infections to trigger a first analysis of their data.

Early in the trials, infection rates were low. With a surge in infections around the globe in October and November, trial participants became infected more quickly.

Pfizer's final results were based on 170 cases within its trial involving more than 43,000 participants.

Moderna conducted its interim analysis after 95 participants developed Covid-19, while Russia's examination was conducted after 20 volunteers developed the disease.

AstraZeneca said its interim analysis was based on 131 infections among participants who received the vaccine and those in a control group who were given an established meningitis shot.

How well are the vaccines supposed to work?

The World Health Organisation ideally wants to see at least 70 per cent efficacy in trials.

The US Food and Drug Administration wants at least 50 per cent - which means there must be at least twice as many infections among volunteers who received a placebo as among those in the vaccine group.

The European Medicines Agency has said it may accept a lower efficacy level.

When will regulators rule on safety and efficacy?

Pfizer/BioNTech plan to submit an EUA application in the United States within days.

Moderna aims to file an application in the coming weeks once it has the two months of safety data on half the trial participants, as required by the US Food and Drug Administration.

That should happen in the second half of November.

That means an FDA decision is unlikely before December.

AstraZeneca said on Monday it will immediately prepare regulatory submission of the data to the authorities around the world that have a framework in place for conditional or early approval.

Regulators for Europe, Britain and Canada are considering data as it becomes available.

It is not clear when companies will submit efficacy data or when the agencies would make a decision.

Could these be the first widely available coronavirus vaccines?

Yes, although China launched an emergency use programme in July aimed at essential workers and others at high risk of infection that has vaccinated hundreds of thousands of people.

At least four Chinese vaccines are far along, including those from China National Biotec Group (CNBG), CanSino Biologics and Sinovac Biotech.

Sinovac said on Nov 18 that mid-stage trial results showed its CoronaVac vaccine triggered a quick immune response, but the level of antibodies produced was lower than in people who had recovered from the disease.

CNBG has said it expects early trial data as soon as November.

Russia has also given the Sputnik V vaccine developed by the Gamaleya Institute to 10,000 members of the general population considered at high risk of contracting the virus.