How does Oxford's coronavirus vaccine differ from other jabs under development?

Illustrative picture of coronavirus vaccine under trail
Three coronavirus vaccine candidates in particular are generating buzz after producing promising study results. (Stock, Getty Images)

Interim data suggests the University of Oxford’s coronavirus vaccine candidate is at least 70% effective at preventing the infection.

In a study of more than 20,000 volunteers, 30 coronavirus cases arose among those who had two doses of the jab, compared to 101 incidences in the participants who had dummy injections – the control arm of the trial.

Boris Johnson and medical experts alike have described the results as “fantastic”, “tremendously exciting” and a “Herculean achievement”.

Others have pointed out, however, the Oxford team’s vaccine does not appear to be as effective as the jabs being developed by Pfizer or Moderna, which demonstrated 90% and 95% efficacy, respectively.

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This may be overly simplistic, however, with preliminary data suggesting the Oxford candidate could be up to 90% effective if the dose is tweaked, as well as it being easier to store than the other vaccines under development.

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Face coverings may continue to be enforced in public enclosed spaces until an effective coronavirus vaccine is rolled out. (Posed by a model, Getty Images)

Experts have repeatedly stressed developing a coronavirus vaccine is not a competition, with multiple pharmaceutical firms having to create and distribute an effective jab to get a handle on the pandemic.

While regulatory approval has not yet been granted for any of the vaccines, the UK government has pre-ordered 100 million doses of the Oxford jab, enough to immunise 50 million people under its existing regimen.

With the latest study suggesting an initial half dose may be more effective than two full doses, the government’s order could spread even further.

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The UK has also pre-ordered 40 million doses of the Pfizer vaccine, of which 10 million should be available by the end of 2020.

When it comes to Moderna’s candidate, the UK government has announced it will have five million doses – enough to vaccinate 2.5 million people – by spring.

How effective are the different vaccines?

The Oxford scientists calculated their vaccine candidate has an overall protection rate of 70%, based on the number of cases that arose in the volunteers who did or did not receive the jab.

When the volunteers were given two high doses of the vaccine, the protection rate was 62%.

Perhaps surprisingly, this rose to 90% when they received a low dose followed by a high one.

It is unclear exactly why this occurred, with the immune response generally increasing in proportion to a vaccine’s dose.

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“We think giving a smaller first dose primes the immune system,” said researcher Professor Andrew Pollard.

His colleague Professor Sarah Gilbert wondered whether exposing an individual to a smaller dose initially may better mimic the conditions of a real infection.

“With vaccines, we always want to fool the immune system that there’s a dangerous infection it needs to respond to in a very safe way,” she said.

“Giving a small amount of the vaccine to start with and following up with a larger amount may be a better way of kicking the immune system into action.”

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On 9 November, Pfizer and the biotechnology firm BioNtech revealed their two-dose vaccine candidate appears to be more than 90% effective at warding off the coronavirus when given 21 days apart.

Two doses of Moderna’s jab, administered four weeks apart, is said to be nearly 95% effective at protecting against the infection.

Professor Pollard stressed each study has a slightly different outcome when it comes to what a vaccine candidate is trying to prevent, which will only become clear once full data on the trials is published, rather than just press releases.

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“We don’t know exactly what everyone is measuring in the trials until we get the full data sets out,” he said.

“We know from the [trial] protocols that what we’re measuring as COVID disease [caused by the coronavirus] is slightly different [from other scientists].”

None of the participants who received the Oxford vaccine at any dose developed severe disease or were admitted to hospital with coronavirus complications.

The Oxford scientists also observed a reduction in asymptomatic cases, which are thought to drive transmission as infectious individuals do not know to isolate.

It is unclear whether the Pfizer and Moderna jabs have the same effect.

How do the vaccines work?

The Oxford jab is made from a weakened version of a common cold virus that usually infects chimpanzees, but has been genetically altered to grow in humans.

While the vaccine does not cause the coronavirus to take hold, it carries genes for the infection’s spike protein, which the virus uses to invade cells.

After the jab is administered, the body produces the spike protein, which the immune system launches a response against.

If the coronavirus is encountered in real life, the immune cells are then primed to fight off the infection.

The Pfizer and Moderna jabs are unique in that they were developed via mRNA technology, which is typically used for cancer therapies.

Individuals are injected with part of the virus’ genetic code, which instructs cells to generate the spike protein, leading to an immune response.

3d visualization of corona virus scene
Since the coronavirus outbreak was identified at the end of 2019, more than 58 million cases have been confirmed worldwide. (Stock, Getty Images)

Which of the vaccines is easiest to distribute?

Enthusiasm was slightly tempered for Pfizer’s vaccine when it emerged the same mRNA technology that enabled the jab to be developed quickly also means it has to be stored at around -80C (-112F).

While Moderna’s candidate was developed using the same technology, it can reportedly be stored at -20C (-4F) for up to six months.

More traditional vaccines that administer part of a virus, or an inactivated but whole pathogen, are typically kept at between 2C (35.6F) and 8C (46.4F).

Experts have had a mixed response to how big a concern these cold temperature storages are.

Professor Toby Peters from the University of Birmingham said: “Nowhere on the planet does the logistical capacity exist to distribute vaccines at this temperature and volume without massive investment.”

Dr Colin Butter from the University of Lincoln argued the the issue was “not insurmountable”.

The Oxford scientists have said common-cold based vaccines have the “significant benefit that they are stable, easily manufactured, transported and stored at domestic fridge temperature (2-8C/35.6-46.4F)”.

“This means they can be easily distributed using existing medical facilities such as doctor’s surgeries and local pharmacies, allowing for the vaccine, if approved, to be deployed very rapidly,” added the team.

Professor Azra Ghani from Imperial College London agreed, adding: “A particular strength of this vaccine is it can be stored in a fridge.

“This means it can be distributed around the world using existing delivery mechanisms.

“This could therefore have a truly significant impact across the globe and enable an end to the COVID-19 pandemic.”

What don’t we know?

Long-term data is lacking for all of the vaccine candidates, leaving doctors and officials unclear exactly how long the jabs may protect against the coronavirus for.

Speaking of the Oxford vaccine’s durability, Professor Pollard said: “It’s too early to say. We only gave second doses in the UK in August.” The ongoing trial is also being carried out in Brazil and South Africa.

The same lingering question surrounds the Pfizer and Moderna jabs.

Early in the outbreak, statistics flagged the elderly and those with underlying health issues are significantly more likely to develop coronavirus complications.

On 19 November, the Oxford team announced that in its trial of 560 healthy adults – of whom 240 were over 70 – their vaccine brought about a similar immune response among all the participants.

Preliminary data on Pfizer’s jab suggests it protects 94% of adults over 65.

When its comes to Moderna’s vaccine, the firm’s chief medical officer Tal Zaks told the BBC the jab “does not appear to lose its potency” with age.

Full data is lacking, however, with it also being unclear to what extent the vaccine candidates protect people with underlying health conditions.

Safety information on the different vaccines is also required, however, all three jabs are thought to just cause typical injection side-effects, like a sore arm, headache, fatigue and fever.

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