The promising news over the effectiveness of the Pfizer coronavirus vaccine will leave many asking how soon a safe jab could be rolled out to help tackle the pandemic.

So what are the regulatory hurdles scientists need to clear before a vaccine can be used on the general population?

– How are vaccines developed?

There are more than 200 Covid-19 vaccine candidates in clinical trials around the world, investigating a range of approaches to help our bodies defend against infection.

Vaccine research goes through a number of stages, starting with early laboratory work and testing on animals such as mice.

Clinical trials on humans progress through three phases, with the first tests being on small groups of up to 100 people to assess the safety of a vaccine.

At a second phase a larger group of several hundred people is used to check if a vaccine consistently works, while a third phase could involve several thousand people to gather statistically significant data on a vaccine’s safety and efficacy.

Clinical trials can normally take years, but due to the pressing need significant global investment and scientific collaboration during the pandemic has helped accelerate research processes.

– How is a new vaccine licensed?

If trials go well, the next stage involves an expert review of all data by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) or the European Medicines Agency (EMA).

Public safety comes first and regulators check that trials show a vaccine meets high standards of safety and effectiveness before granting a licence.

The MHRA said data to be reviewed must include results from the lab and clinical trials in humans; manufacturing and quality controls, product sampling, and testing of the final product. The factories where vaccines are made are also inspected before approval.

– Who else is involved in the decision-making process?

Once the MHRA has reviewed the data, it will seek advice from the Government’s independent advisory body, the Commission on Human Medicines.

They will also critically assess the data before advising the Government on the safety, quality and effectiveness of any potential vaccine.

The Joint Committee on Vaccination and Immunisation (JCVI) will advise the Government about the use of a vaccine.

The JCVI’s interim guidance says that older adults in care homes and care home workers should get priority, followed by those aged 80 and over, and health and social care workers.

– How long could a potential vaccine approval process take?

The MHRA has been working to ensure that it prioritises reviews of Covid vaccines.

This process usually takes place at the end of the clinical trial process, but for some vaccine candidates the MHRA has said it will carry out a rolling data review to speed up the process.

The MHRA said: “We will quickly and rigorously assess the data in the shortest time possible, without compromising the thoroughness of our review.”

– What stage is the Pfizer vaccine at?

Pfizer said the first set of results from its Phase 3 Covid-19 vaccine trial, which enrolled some 43,538 participants, provides initial evidence of its ability to prevent the virus.

However, these are interim findings which are yet to be peer-reviewed and with more studies to follow.

Pfizer, working alongside German biotech company BioNTech, said it plans to apply to the US medicines regulator the Food and Drug Administration (FDA) for emergency approval to use the vaccine by the end of the month.

– If the vaccine is approved in the US first, is it also approved in the UK?

No. Any vaccine for use in the UK will need the separate approval of the MHRA or, up to December 31, the EMA.

– How does Brexit affect vaccine approval?

From January 1 next year, after the end of the Brexit transition period, the MHRA will be the UK’s standalone medicines and medical devices regulator, but it can still recognise the decisions of the EMA after that date.

Before the referendum a lot of Britain’s regulatory work was closely linked to that of the EMA.

When medicines were approved by European regulators this would help steer the decisions for which drugs or medical products could be used in Britain.

In October, new law came into force to allow the MHRA to authorise temporary supply for vaccines if one becomes available before 2021.

This means that if a vaccine is found to meet standards of safety, quality and effectiveness by the MHRA then vaccinations can begin without needing to wait for the EMA.