Preliminary results from the trials of the Covid-19 vaccine jointly developed by the University of Oxford and AstraZeneca indicate that the vaccine’s overall efficacy is 70% but that a regimen that calls for a lower first dose is 90% effective.
The preliminary results on the AstraZeneca vaccine were based on a total of 131 Covid-19 cases in a study involving 11,363 participants. The findings were perplexing. Two full doses of the vaccine appeared to be only 62% effective at preventing disease, while a half dose, followed by a full dose, was about 90% effective. That latter analysis was conducted on a small subset of the study participants, only 2,741.
Hopefully more study will be done on that dosage question. From the AP:
“The report that an initial half-dose is better than a full dose seems counterintuitive for those of us thinking of vaccines as normal drugs: With drugs, we expect that higher doses have bigger effects, and more side-effects,” he said. “But the immune system does not work like that.”
The seemingly lower efficacy comes with some perhaps significant benefits: this vaccine is cheaper to produce and doesn’t require any special refrigeration.
The vaccine can be transported under “normal refrigerated conditions” of 2 to 8 degrees Celsius (36 to 46 degrees Fahrenheit), AstraZeneca said. By comparison, Pfizer plans to distribute its vaccine using specially designed “thermal shippers” that use dry ice to maintain temperatures of minus-70 degrees Celsius (minus-94 degrees Fahrenheit).
The Pfizer and Moderna vaccines were pretty similar in many respects and this one seems quite different. These results were just released a few hours ago, so it will be interesting to follow the debate and expert commentary on this. Stay tuned…
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