PandemicPreparedness

18 December: Two publications on the earlier Phase 1/2 trial results of the Oxford-AstraZeneca vaccine, ChAdOx1 nCoV-19, have been published in Nature Medicine. The first found that a full dose booster shot was well-tolerated and induces a good immune response. The second details the immune mechanisms which are stimulated by this vaccine, with the authors concluding "strong humoral and cellular immune responses” are achieved.

The results from the Phase 1/2 safety and efficacy trials formed the basis for progression to Phase 3 efficacy trials, and provided the rationale for switching to a two-dose regime.

8 December: Data published in The Lancet has confirmed that the Oxford/AstraZeneca vaccine is safe and highly effective in preventing COVID-19, stating that the efficacy is 90% if given as half dose first, followed by a full dose. If the vaccine is administered in two full doses, its efficacy is 62%.

There have been no reports of hospitalisations or severe disease among the volunteers. The majority of the participants were between 18 and 55 years of age, and so vaccine efficacy in older age groups could not be assessed because there were too few cases.

25 November: The manufacturers of the vaccine released information that there was a dosage error during their trial. One of the dosing schedules trialed involved half a dose initially, then a full-dose booster a month later (as reported below.) The company now states that the half-dose regimen was not planned, but was an error. Only about 2,800 of the nearly 13,000 trial participants received the half-dose/full dose; the majority had two full doses, as planned.

It is not clear if any of the people in the half-dose group were over 55 years old. Data about the vaccine's efficacy in older adults is crucial, as they are more at risk for severe COVID-19 infections and are thus a priority group for vaccination. The company's CEO said they expect to do an additional trial, possibly outside of the United States, to validate these initial findings.

23 November:

A dosing regimen of the Oxford/AstraZeneca vaccine candidate (ChAdOx1 nCoV-19) has been found to prevent up to 90% of COVID-19 infections.

Two dosing regimens were tested and differing efficacy was found:

• Half dose followed by a full dose at least one month apart: 90% efficacy
• Two full doses given at least one month apart: 62% efficacy

Average efficacy: 70%

There were a total of 131 COVID-19 cases in the interim analysis and no hospitalisations or severe cases of the disease were reported in participants receiving the vaccine. No serious safety events related to the vaccine were confirmed.

Professor Andrew Pollard, Chief Investigator of the Oxford Vaccine Trial at Oxford, said: "These findings show that we have an effective vaccine that will save many lives."

"Excitingly, we’ve found that one of our dosing regimens may be around 90% effective and, if this dosing regime is used, more people could be vaccinated with the planned vaccine supply."

"Today’s announcement is only possible thanks to the many volunteers in our trial, and the hard working and talented team of researchers based around the world.”