What’s behind the efficacy results?

The UK will become the first country in the world to implement the coronavirus vaccine developed by the University of Oxford and AstraZeneca, in what could be a historic moment in the fight against Covid-19.

The vaccine is cheaper and easier to distribute than the Pfizer-BioNTech alternative. But its efficacy results, while still high, are not so straightforward.

Provisional data published in the lancet earlier this month it gave the AstraZeneca-Oxford vaccine an overall efficacy of 70.4%. This is less than the 95% efficacy of the Pfizer-BioNTech vaccine, but it is still a remarkable figure compared to the seasonal flu vaccine.

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Although efficacy varies from year to year, studies show that the vaccine reduces the risk of getting the flu by between 40% and 60% in the entire general population, as the CDC notes.

Different dosage regimens

A complication with the AstraZeneca-Oxford figure is the fact that it reflects data from two different dosing regimens. The trials showed that two full doses of the vaccine provided 62% efficacy, while a lower dose followed by a full dose appeared to provide 90% efficacy.

Although that second number is higher, it comes from a much smaller group of participants. While 4,440 volunteers received two full doses of the vaccine, only 1,367 volunteers received the low dose followed by a full dose.

The efficacy figures for each group were calculated by comparing the number of people who received the vaccine and developed Covid-19 with a similar number of people who received a placebo.

Dr. David Thompson of the coronavirus testing company Medic Testing said scientists are still not sure why different dosing regimens produced different results. He told me, “No one knows, just yet, there are some theories. The first is that the lower dose better prepares the immune system to produce antibodies.

“The second theory is that this is simply the result of a study with fewer participants, which means that the results are not as accurate and reflect a problem with the study design.”

He added that the low-dose study involved younger and fitter participants, so it’s not yet clear how effective this regimen would be in an older population.

Synchronization

As the Guardian You see, regulators rejected the 90% finding on more detailed analysis. It is believed that time may have played a role in the smaller group’s efficacy results, as many of these volunteers received their second dose later than normal.

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Professor Andrew Pollard, a member of the UK Joint Committee on Vaccination and Immunization, told the publication: “If you have a longer gap between the first and second doses, then the strength of the boost tends to be stronger. So that’s not a surprise or unusual. That’s what we see with almost every other vaccine that has been tested. ”

For now, at least, people in the UK are expected to get two full doses. Reece Samani of Signature Pharmacy explained: “Currently, only the standard dosing regimen, two full doses four to 12 weeks apart, has obtained regulatory approval.”

But this may change as new data comes in, Samani added.

Restrictions

For now, restrictions in the UK are unlikely to ease as a result of vaccines. But eventually they could see that life was returning to relative normality. Samani told me: “Although we will not see the benefits of the vaccine for a few months, I think it will be significant. It will continue to be necessary to guarantee social distancing, the use of masks, hand washing, etc., but the tranquility provided by the vaccine will allow an eventual relaxation of the restrictions ”.

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Dr Thompson added: “When a sufficient number of the UK population is protected by vaccines, we can hope that the level of threat will decrease … and the UK can return to a more normal way of life.

“This may still take months, however, as vaccine distribution focuses first on health professionals and the vulnerable.”