COVID-19 vaccine: A saviour, at last?

Pearl Toh
19 Dec 2020

With the release of the latest interim efficacy results for ChAdOx1 nCoV-19, the adenovirus-vectored vaccine against COVID-19 is inching a step closer towards regulatory approval — and eventually, widespread use that will hopefully put an end to the relentless carnage by the pandemic.

Data from late-stage human trials showed that the efficacy of ChAdOx1 nCoV-19 could be as high as 90 percent in preventing symptomatic COVID-19, at least among volunteers who initially received a lower (half) dose followed by a standard full dose, at least 1 month apart. [Lancet 2020;doi:10.1016/S0140-6736(20)32661-1]

Under the other dosing regimen, whereby participants were given two standard doses, efficacy was 62.1 percent. Pooling the data from both dosing regimens yielded an overall efficacy of 70.4 percent.

“The combined efficacy of 70 percent doesn’t actually matter — as when it comes down to it, you will get one or the other dosing regimen with that particular efficacy,” commented Professor Julian Tang from the University of Leicester, UK.

Excitingly, we have found that one of our dosing regimens may be around 90 percent effective and if this dosing regimen is used, more people could be vaccinated with [the constrained] vaccine supply,” said lead investigator Professor Andrew Pollard from the University of Oxford, UK.

A minimum efficacy of 50 percent is required for regulatory approval, based on the US FDA guidelines and the WHO criteria for COVID-19 vaccine. The figures for ChAdOx1 nCoV-19 have exceeded this threshold, regardless of the dosing regimen.

The interim data came from 11,636 participants enrolled in the phase II/III trials in the UK and Brazil, who were randomized 1:1 to receive ChAdOx1 nCoV-19 vaccine or control injection with a meningococcal vaccine or saline solution. ChAdOx1 nCoV-19 vaccine was given in two doses, at least 1 month apart, at standard full doses for both, or half a dose at first followed by a standard dose in a subset of recipients.

Importantly, ChAdOx1 nCoV-19 showed an acceptable safety profile, with no COVID-19-related hospitalizations or severe illness in the ChAdOx1 nCoV-19 arm. In comparison, 10 such hospitalizations occurred in the control arm, two of which were for severe COVID-19, including one fatal case.

There is also an early indication that the vaccine might prevent asymptomatic disease too, though more data are needed to confirm this. When given at half a dose at first, followed by a standard dose, the rates of asymptomatic infections were lower in the ChAdOx1 nCoV-19 arm vs the control arm (0.6 percent vs 1.5 percent; 58.9 percent for efficacy).

“While a vaccine that could prevent COVID-19 would have a substantial public health benefit, prevention of asymptomatic infection could reduce viral transmission and protect those with underlying health conditions who do not respond to vaccination [or those not vaccinated] … providing wider benefit for the society,” the researchers  explained.

A game changer?

Unlike the mRNA vaccines which required ultra-low temperature freezers for storage, “the [ChAdOx1 nCoV-19] vaccine can be stored and distributed at 2–8°C, making it particularly suitable for global distribution,” highlighted Pollard and co-authors.

This storage advantage can be potentially game-changing, according to Sir Jeremy Farrar, director of the Wellcome Trust, UK, who noted, “if you have to store vaccines on dry ice that brings additional challenges of how to get it into villages in the UK, let alone villages in sub-Saharan Africa, and Brazil.”

The investigators of ChAdOx1 nCoV-19 have also nailed down a deal with the manufacturer to provide the vaccine on a not-for-profit basis worldwide, and at cost price during the pandemic for low- and middle-income countries to ensure equitable access to the vaccine.

The beginning of the end?

Currently, two mRNA vaccines have been rolled out as of this writing, with more than 90 percent efficacy.

“The possibility that more than one efficacious vaccine against COVID-19 might be approved for use in the near future is encouraging,” said co-lead investigator Professor Sarah Gilbert from the University of Oxford, who noted that no one single manufacturer would be able to come out with doses large enough to meet global demand.

Also equally likely, the world would need more than one vaccine to target different subgroups of people, for instance, based on age or health conditions.

Still, further questions remain with regard to durability of protection from these vaccines — and ongoing trials will continue to follow the participants to gather more clarity.  

“Efficacy is an important consideration, but so are pragmatics of delivery, community acceptance, longevity of effect, whether a vaccine reduces infection and transmission as well as disease, efficacy in high-risk groups, and, of course, safety,” wrote Drs Maria Deloria Knoll and Chizoba Wonodi from the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, US, in a linked commentary. [Lancet 2020;doi:10.1016/S0140-6736(20)32623-4]

Meanwhile, the pandemic is far from over. As of this writing, COVID-19 cases worldwide stood at over 74 million, claiming 1.65 million lives.

Until widespread immunity halts the spread of SARS-CoV-2, physical distancing measures and novel therapies are needed to control COVID-19,” said Pollard and co-authors.

But, at least, there is light at the end of the long dark tunnel — and the light is getting brighter with more and more positive news on vaccine development.

“Despite the outstanding questions and challenges in delivering these vaccines, it is hard not to be excited about these findings and the existence of three safe and efficacious COVID-19 vaccines, with a further 55 [other vaccines] already in clinical trials,” Knoll and Wonodi pointed out.

“Perhaps by this time next year, we can celebrate the global control of SARS-CoV-2, in person,” they quipped, in hope.

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