While the latter two reportedly showed around 95% efficacy in Phase 3 trials, the candidate the Anglo-Swedish drugmaker is developing for Oxford University achieved what it said was 70% average efficacy based on the result for two regimens. The larger cohort of 8,895 volunteers received two full doses while a smaller cohort of 2,741 got a half dose followed by a full booster shot.

The vaccine’s efficacy in those receiving the two full doses was shown to be 62%, compared with 90% in those who began with a half dose. None of the subjects receiving the vaccine was hospitalized or had a severe case of Covid-19, AZ said. Altogether, there were 131 Covid-19 cases present in the interim analysis.

The trials described were carried out in the UK and Brazil. Additional trials are in progress in the US, Japan, Russia, South Africa, Kenya and Latin America, with studies now on the agenda in other European and Asian countries. Up to 60,000 participants are expected to be enrolled globally.

On the drugmaker’s news, pharmacologists speculated on why efficacy for the viral vector vaccine was lower than for the mRNA vaccines. Some thought the small number of subjects in AZ’s half-dose trial cohort distorted the comparison. Others believed differences between the designs of the trials may have played a role, noting also that the Pfiizer/BioNTech tests were conducted mainly with diverse populations and AZ’s mainly with Caucasian volunteers.

As data continues to accumulate, additional analyses will be conducted, AZ said, thus refining the efficacy reading and establishing the duration of protection. The final analysis of interim results will be published as a peer reviewed study in a scientific journal.

According to an independent data safety monitoring board, the Oxford vaccine met its primary endpoint, achieving protection from Covid-19 from 14 days after patients received two doses of the vaccine. No serious safety events directly related to the vaccine were confirmed, and the candidate was well tolerated across both dosing regimens, the board said.

AstraZeneca now plans to begin submission of the data to regulatory authorities in countries that have a framework in place for conditional or early approval. It also will seek an Emergency Use Listing from the World Health Organization for an accelerated pathway to availability in low-income countries.

The company said it is making rapid progress in manufacturing with a capacity of up to 3 billion doses of the vaccine to be rolled out in in 2021, pending regulatory approval. It expects to sell these doses next on a non-profit basis for around $3 a dose in 2021, as announced.

Author: Dede Williams, Freelance Journalist