What do the new results from the Oxford/Astrazeneca vaccine trial mean?


A: More good news! While efficacy was not as high as that reported in the recent Pfizer and Moderna trials, this vaccine has some important advantages with regard to cost and ease of storage. But as with much of the recent “science by press release,” we’ll be anxiously awaiting further details.

For the 3rd Monday in a row, we awoke to happy results from a Phase III clinical trial for a COVID-19 vaccine. The headlines were a bit confusing however, with some citing 70% efficacy and some “up to 90%” efficacy.

Why the confusing headlines? It turns out the Oxford vaccine used two different dosing regimes (accidentally at first-see link below). The first and second doses were given one month apart:

Two full doses (8,895 participants): 62% efficacy

Half dose + full dose (2,741 participants): 90% efficacy

Pooled results for both regimes: 70% efficacy

What does efficacy mean again? TL;DR it is the % reduction in infection between those vaccinated and those receiving a placebo. For 131 infections, a 70% reduction means that around 100 people in the placebo group were infected versus around 30 in the vaccine group.

❓Why on earth would a half first dose be more effective than a full dose? Scientists aren’t yet sure, but a couple of hypotheses have been proposed:

➡️ Vector immunity: the vaccine uses an altered chimpanzee adenovirus (cold virus) to deliver the famous SARS-CoV-2 spike protein gene into our cells, which then manufacture the spike protein thus illiciting an immune response. A high initial dose may produce more of a response to the adenovirus and not enough to spike protein. The half dose may hit the sweet spot.

➡️ Priming: Professor Andrew Pollard, director of the Oxford vaccine group said “…by giving a smaller first dose we’re priming the immune system differently, we’re setting it up better to respond.”
Professor Sarah Gilbert whose team created the vaccine said: “It could be that by giving a small amount of the vaccine to start with and following up with a bigger amount, that’s a better way of kicking the immune system into action and giving us the strongest immune response.”

➡️ Statistical fluke: Given the relatively small numbers in the half-dose group (we don’t yet know how many infections were seen in that group), these results might be imprecise, and the two dosing regimes may actually have more similar efficacy results. As more cases accrue in both groups we can say with more statistical certainty whether they are the same or different.

Despite the somewhat confusing dosing and possible lower efficacy numbers, the results are very welcome for several reasons:

💥 Prior to the Pfizer/Moderna news, we would have thought 70% efficacy was great! This will still do a lot to reduce the burden of COVID-19 infections and deaths globally.

🏥 There were NO hospitalizations or severe cases in the vaccine group.

😷 Suggestive evidence that the vaccine may also prevent asymptomatic infection—parts of this trial swabbed participants every week rather than waiting for symptoms.

💰Cheaper: $2.50 per dose compared to $15-25 for Pfizer and Moderna.

🌡️ Storage: The vaccine can be transported and stored at regular refrigerator temperatures (2-8 degrees Celsius/ 36-46 degrees Fahrenheit) for at least six months, making it much easier to distribute around the world.

🌎 More vaccine may be available sooner. Astrazeneca estimates it will have 200 million doses ready by the end of 2020, and capacity to produce 100-200 million does per month. If the half dose is indeed the preferred first dosing, even more supply will be available.

Given the number of people to vaccinate worldwide to truly beat down this virus, multiple effective vaccines will be key, and the cheaper and easier to distribute the better.

As with the Pfizer and Moderna vaccine, trials are continuing and thus results may change as new information comes in—watch this space for updates.

Remember, with vaccines poised and ready to give very soon to our most vulnerable, we should be EVEN MORE careful than ever going into this holiday season. A COVID-19 infection and death averted now may NEVER have to happen. Thank you SCIENCE!!!

Stay safe, Stay sane.

Those Nerdy Girls

Further reading:

Why Oxford’s positive vaccine results are puzzling scientists

Why the Oxford Astrazeneca vaccine is now a global game changer

Lucky dosing error

Astrazeneca Press Release

Link to original FB post