AstraZeneca efficacy: how effective is the Oxford vaccine - and how do Pfizer, Moderna and Novavax compare?

AstraZeneca has said its vaccine has a 100 per cent efficacy against severe or critical disease and hospitalisation due to Covid-19

AstraZeneca has revealed that its vaccine is 76 per cent effective against symptomatic Covid-19.

The revised results come after the company updated its analysis of the third phase of testing, and follows a figures released on Monday (22 March) which reported a 79 per cent efficacy which US federal health officials said was based on “outdated information”.

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The company, which developed the jab with the University of Oxford, was forced to defend its use of vaccine data due to US authorities, after the US Data and Safety Monitoring Board said it was concerned that AstraZeneca may have provided an incomplete view of the efficacy data.

The AstraZeneca vaccine is 85% effective against symptomatic Covid-19 in patients aged 65 and over (Photo: Getty Images)

The pharmaceutical company said in a statement on Thursday (25 March) that its latest analysis confirms “vaccine efficacy consistent with the prespecified interim analysis” announced on Monday.

But how does the efficacy of the vaccine compare to other Covid-19 jabs that are currently available? Here’s what you need to know.

How effective is the AstraZeneca vaccine?

AstraZeneca has said its vaccine has a 100 per cent efficacy against severe or critical disease and hospitalisation due to Covid-19, and is 85 per cent effective against symptomatic Covid-19 in patients aged 65 and over.

Analysis from a trial of more than 32,400 participants found that in 190 symptomatic cases, an efficacy of 76 per cent was observed 15 days or more after two doses were given four weeks apart.

AstraZeneca said it hopes the vaccine will protect against severe disease from all Covid-19 variants, and it has been declared safe and effective by the European Medicines Agency, the World Health Organisation and the Medicines and Healthcare products Regulatory Agency (MHRA).

Mene Pangalos, AstraZeneca's executive vice president of biopharmaceutical research and development, said: “The primary analysis is consistent with our previously released interim analysis, and confirms that our Covid-19 vaccine is highly effective in adults, including those aged 65 years and over.

“We look forward to filing our regulatory submission for Emergency Use Authorisation in the US and preparing for the rollout of millions of doses across America.”

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How effective is the Pfizer vaccine?

The Pfizer Covid-19 vaccine has been found to generate a strong immune response in 99 per cent of people after just one dose.

The vaccine has recorded the highest efficacy in trials, providing 95 per cent protection after both doses.

It is also 94 per cent effective among those aged 65 and over, with the first dose giving 52 per cent protection after 12 days.

Protection against severe disease after both doses of the vaccine are even stronger, with scientists saying that the second jab is vital to ensure maximum protection and to provide a lasting defence against the virus.

How effective is the Moderna vaccine?

A single dose of the Moderna Covid-19 vaccine has a similar efficacy level to the Pfizer vaccine, with trial results finding that it is 92 per cent effective.

The vaccine works in a similar way to the jab from Pfizer and requires temperatures of around -20C for shipping, which is similar to a normal freezer. However, it does not require the same ultracold storage as Pfizer’s and can remain stable at normal fridge temperature for 30 days.

Both the Moderna and Pfizer vaccines use synthetic messenger RNA (mRNA), a genetic material that contains information about the spike protein (the part of the virus which enters human cells).

The vaccines provide the body with instructions to produce a small amount of this protein which, once detected by the immune system, leads to a protective antibody response.

Trial results also indicate that the vaccine is generally well tolerated with no serious safety concerns.

How effective is the Novavax vaccine?

Results from large scale trials have found the Novavax vaccine to be highly effective against preventing serious illness or hospitalisations from Covid-19 infection.

The UK study, which had 15,000 participants aged between 18 to 84 years, found that the vaccine was 96.4 per cent effective against the original strain of coronavirus, and 86.3 per cent effective against the Kent variant, which has become the dominant strain in the UK over the winter.

The vaccine is also shown to have a lower effectiveness, between 48.6 and 55.4 per cent, against the South African coronavirus strain, highlighting the need for boosters.