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Coronavirus vaccine: AstraZeneca could expand US trial to pursue 90% efficacious vaccine

Anjalee Khemlani
·Senior Reporter
·5 min read

AstraZeneca’s (AZN) positive interim results for its COVID-19 vaccine Monday was met with some confusion as health experts and Wall Street attempted to parse the company’s “up to 90%” and “average 70%” vaccine efficacy claims.

The vaccine candidate was tested in two different ways, resulting in two different efficacy rates — 62% and 90%— which the company averaged at 70%. The lower efficacy was from two full doses given a month apart, the higher efficacy came from the first dose being halved followed by a full booster.

But that confused health experts and irked some analysts.

“I’m completely surprised. I don’t understand it, ” said Dr. Arthur Caplan, a leading bioethicist and professor at New York University Langone Medical Center, about why the company chose to test the two regimens so late in the game, and why the weaker regimen provided stronger protection.

He wasn’t alone. Other top vaccine experts like Baylor College of Medicine’s Dr. Peter Hotez and Children’s Hospital of Pennsylvania’s Dr. Paul Offit made similar statements in interviews with Yahoo Finance Monday.

“It’s science by press release and really hard to know what’s going on,” Offit said.

What do the numbers mean?

The 62% efficacy of a full-dose regimen was intriguing for many, with some wondering if previous concerns about an adenovirus vector platform — which both AstraZeneca and some Chinese vaccine candidates are using — were at play. Johnson & Johnson is also using a similar platform, but it is unlikely to see the same issue, some experts said.

Unlike Pfizer (PFE)/BioNTech (BNTX) and Moderna (MRNA), which are using a new synthetic technology called messenger RNA, AstraZeneca is using a synthetic coding in an inactive virus to deliver the vaccine.

Hotez surmised the first shot induced more antibodies that inhibited a second dose. Adenovirus-based vaccines can sometimes render the body immune to a second shot of the same vaccine.

But even with a lower efficacy than Pfizer and Moderna, which both came in at about 95%, Hotez noted that the real world efficacy is still unknown.

“These efficacy numbers may fluctuate as we vaccinate the entire U.S. population,” he said.

SVB Leerink analysts were less forgiving, saying AstraZeneca, and partner Oxford University, embellished the results to present a higher efficacy.

“The suggestion by the inventors that the small sample given the lower priming dose was evidence of superior efficacy only brings discredit to the program,” said analyst Geoffrey Porges.

He added, “It appears that the occurrence of pre existing or post vaccination immunity to the vector has a significant dampening effect on the efficacy of the vaccines.”

NYU’s Caplan noted that even with the data released from any vaccine trial, much still remains unknown about the vaccines.

Which age group, ethnicity or disease state does or does not work better with a specific vaccine, as well as the durability of protection and ability to block transmission all remain unknown, he said.

Which means that even as the regulatory bodies globally prepare to evaluate the data, much remains to be known.

Porges said, “We regard the data disclosure as premature and insufficient.”

The company will submit for emergency use to the World Health Organization, which will allow low- and middle-income countries to have a vaccine candidate that doesn’t require special shipping and handling.

Other SVB Leerink analysts said as much Monday.

“Despite apparent inferiority vs the mRNA drugs, we think there are some attributes of the program that are important, especially during the first wave of vaccines at the height of the pandemic, where demand will significantly outstrip supply,” they said.

FILE - In this Thursday, April 23, 2020 file screen grab taken from video issued by Britain's Oxford University, showing a person being injected as part of the first human trials in the UK to test a potential coronavirus vaccine, untaken by Oxford University in England. AstraZeneca says late-stage trials of its COVID-19 vaccine were “highly effective’’ in preventing disease. A vaccine developed by AstraZeneca and the University of Oxford prevented 70% of people from developing the coronavirus in late-stage trials, the team reported Monday Nov. 23, 2020. (Oxford University Pool via AP, File)
AstraZeneca says late-stage trials of its COVID-19 vaccine were “highly effective’’ in preventing disease. A vaccine developed by AstraZeneca and the University of Oxford prevented 70% of people from developing the coronavirus in late-stage trials, the team reported Monday Nov. 23, 2020. (Oxford University Pool via AP, File)

Doubling down on halving the dose

AstraZeneca’s U.S. head Ruud Dobber told Yahoo Finance the company will be engaging with the U.S. Food and Drug Administration (FDA) to discuss the U.S. trial and potentially add a new arm in the late-stage trial to include the half-dose primer.

“Overall, I think that the data set is very comprehensive and very positive, Dobber said.

When asked about the reason behind the change in dosage and why the higher dose wasn’t as efficacious, AstraZeneca declined to comment. One executive told The Guardian the half dose was an accident. But why it resulted in higher efficacy remains unknown.

But it is clear the company is excited about the discovery and intends to pursue the half-dose prime, full-dose booster regimen further in ongoing trials.

In an emailed statement Tuesday, a spokesperson said, “We see a lot of merit in this regimen and we will now start discussions with regulators into incorporating this dose combination for further clinical investigation. We will continue to follow the science to better understand these data and share in a peer-reviewed journal in due course.”

In a briefing Tuesday, Operation Warp Speed head Moncef Slaoui said that the U.S. trial, which has only recruited 11,000 individuals, or about one-third of its target participants, has only been testing the two full doses. He also noted that those who received the half dose in other trials were younger than 55 years old.

Meanwhile, Dobber said the data for the U.K. and Brazil trials will be released by the end of this week and has been submitted to a peer-review journal.

Among the leading candidates, the company is the only one so far to promise no profit from its vaccine amid the pandemic. The price is about $3 per dose, compared to about $20 and higher for the mRNA candidates.

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