AstraZeneca/Oxford said this week it would assess why its vaccine candidate generated better efficacy at a lower dose. The statement came as the British-Swedish drug maker AstraZeneca started rolling submission of data to regulators across the world, while also battling perception about the varied efficacy data from the trial of the vaccine developed jointly with the University of Oxford.
The vaccine seemed to have worked better during trials in a group of about 2,700 volunteers who had received half the dose in the first round, followed by a full dose after a month, compared with those who received two full doses. The company reported a 90% vaccine efficacy in the first group and 63% in the second.
“We are delighted to study more on this,” Sara Gilbert, professor of vaccinology at the University of Oxford said during a press briefing on November 23 to share the interim results of the vaccine trial. She explained that this result might be because the vaccine was able to better mimic the actual infection.
“What we are able to do with vaccines is fool the immune system into thinking that there is a dangerous infection that it needs to respond to, but we do it in a safe way so that it generates cell response. And it could be possible that giving a small amount of vaccine and following it up with a full dose we get this result,” Gilbert said on Monday, while adding that more work would be needed to study that. Gilbert also has experience in developing a vaccine for the Middle East Respiratory Syndrome (MERS), an infection caused by one form of the coronavirus.
Two divergent vaccine efficacy data raised eyebrows among medical experts and statisticians who asked for more explanations from the company on the results.
“AstraZeneca/Oxford get a poor grade for transparency and rigor when it comes to the vaccine trial results they have reported. This is not like Pfizer or Moderna where we had the protocols in advance and a pre-specified primary analysis was reported,” Natalie Dean, an assistant professor at Biostatistics University of Florida, said in a Twitter post on November 25 after the efficacy data were released.
“All vaccines so far present good news by press release. The Oxford vaccine has safety and immunogenicity on a subset last week, but needs further analysis to link to efficacy results. All vaccines need to go to regulators, of course, but follow quickly with publication” of trial data, said Gagandeep Kang, a vaccine expert and member of the Coalition for Epidemic Preparedness and Innovation.
Vaccine efficacy is different from actual effectiveness. In efficacy data, companies present results from a randomised controlled trial that gives a statistical indication of how the vaccine might work in a real-field setting. The US FDA and most other regulators demand efficacy of at least 50% for a vaccine to get approval.
AstraZeneca is positioning the vaccine as one that could be universally administered and has shown to be safe. Andrew Pollard, chief investigator of the Oxford Vaccine trial, said the vaccine could be stored in usual refrigerated conditions that could help in distribution widely across the world. He said by next month, there would be more data released on the half-dose vaccine efficacy.
While Pfizer and Moderna have manufactured initially 100 million doses, AstraZeneca has manufacturing partnerships with companies in Latin America to Asia including in India (through Serum Institute of India) that would make its product widely accessible.
The vaccine makers, weeks after releasing their efficacy data for the Covid vaccine candidate, are now preparing to position their vaccine platforms to regulators and governments as the most suited for a mass distribution in most parts of the world.
In the last two-week, companies such as Pfizer/BionTech, Moderna and AstraZeneca/Oxford have released their data on the efficacy of their Covid vaccines, with the first two companies reporting a 95% efficacy of their vaccines, compared with 63% and 90% in the two groups by AstraZeneca/Oxford.
While Pfizer and Moderna vaccines have better efficacy, the extremely low temperature requirement of the vaccines makes them a difficult vaccine to roll out in countries such as India.