Pfizer Covid vaccine '90% effective' - but what does this mean?

The news of the vaccine has been widely welcomed. Credit: PA

Hailed as a "great day for science and humanity", a leading candidate coronavirus vaccine has so far surpassed expert expectations.

The pharmaceutical giant Pfizer, working with German biotech company BioNTech, has released interim analysis suggesting their vaccine is more than 90% effective in preventing Covid-19.

So what does this mean and will there be enough vaccine to go around?

Is this big news? Yes. These are interim findings and studies will continue but analysis shows that the Pfizer vaccine can prevent more than 90% of people from getting Covid-19. The vaccine has been tested on 43,500 people in six countries and no safety concerns have been raised.

Pfizer plans to apply to the US regulator the Food and Drug Administration (FDA) for emergency approval to use the vaccine by the end of the month. The analysis was carried out after 94 confirmed cases of Covid-19 were found among those taking part in the trial. What type of vaccine is this?

The jab is known as a messenger RNA (mRNA) vaccine. Conventional vaccines are produced using weakened forms of the virus, but mRNAs use only the virus’s genetic code. An mRNA vaccine is injected into the body where it enters cells and tells them to create antigens. These antigens are recognised by the immune system and prepare it to fight coronavirus. What are the advantages of this type of vaccine? No actual virus is needed to create an mRNA vaccine. This means the rate at which the vaccine can be produced is dramatically accelerated. As a result, mRNA vaccines have been hailed as potentially offering a rapid solution to new outbreaks of infectious diseases. They can also be modified reasonably quickly if, for example, a virus develops mutations and begins to change.

The UK Government was the first to sign an agreement for the Pfizer/BioNTech vaccine Credit: David Cheskin/PA

mRNA vaccines are also cheaper to produce than traditional vaccines. But both will play an important role in tackling Covid-19. Are they safe?

All vaccines undergo rigorous testing and have oversight from experienced regulators. Some believe mRNA vaccines are safer for the patient as they do not rely on any element of the virus being injected into the body. mRNA vaccines have been tried and tested in the lab and on animals but the coronavirus vaccine will be the first one licensed for use in humans. The human trials of mRNA vaccines – involving tens of thousands of people – have been going on since early 2020 to show whether it is safe and effective. Pfizer will continue to collect safety and long-term outcomes data from participants for two years. Do we have enough doses to vaccinate the UK population? The UK has secured 40 million doses of the Pfizer/BioNTech vaccine – the first agreement the firms signed with any government.

The UK will receive 10 million by the end of 2020 if the vaccine is approved. It is thought people will need two doses, meaning not enough shots have been secured for the entire UK population. However, it is likely other vaccines will announce results from their clinical trials shortly.

Which countries will get the vaccine?

Other than the UK, agreements have also been reached with Japan and the European Union, for example, for 120 million and 200 million doses respectively.

If approved, the plan is to supply up to 100 million doses worldwide by the end of 2020 and around 1.3 billion doses by the end of 2021, Pfizer said in August.

Pfizer says: "We are working with governments around the world to provide and distribute our vaccine, if authorized or approved.

"Those governments and local regulatory authorities would provide the vaccine as they determine is appropriate. "

It may prove challenging to distribute a vaccine in low and middle-income countries, but the World Health Organisation will look to support countries with weak regulatory systems.

The hope is that this can speed up the licencing of a vaccine and help to make the doses available for the population.

Who will be vaccinated first? The Joint Committee on Vaccination and Immunisation (JCVI) has examined data on who suffers the worst outcomes from coronavirus and who is at highest risk of death. Its interim guidance says the order of priority should be:

  • Older adults in a care home and care home workers

  • All those aged 80 and over and health and social care workers, though they may move up the list

  • Anyone 75 and over

  • People aged 70 and over

  • All those aged 65 and over

  • High-risk adults under 65

  • Moderate-risk adults under 65

  • All those aged 60 and over

  • All those 55 and over

  • All those aged 50 and over

  • The rest of the population, with priority yet to be determined.