Pfizer and its partner BioNTech have five potential COVID-19 vaccines in clinical trials, each of which is based on a different mRNA format. Now the companies are reporting that the most advanced candidate, BNT162b2, performed well in trials in which mice and macaques were infected with the coronavirus after inoculation.
The companies announced Wednesday that the vaccine candidate produced neutralizing antibodies against SARS-CoV-2, the virus that causes COVID-19, in macaques, as well as antigen-specific CD4+ and CD8+ T cells in both the nonhuman primates and mice. Those T cell responses indicate a "strong" anti-viral immune attack, the companies said. The results were published on the journal preprint site BioRxiv.
Pfizer and BioNTech reported that after one shot and a booster shot, the macaques that had been challenged with the COVID-19 virus had no viral RNA in their lower respiratory tracts, as compared to non-immunized animals, most of which did show evidence of the viral RNA.
According to the study, two shots of BNT162b2 given to the macaques induced COVID-19 neutralizing antibodies at levels that were 10.2 to 18 times higher than those found in convalescent plasma from human patients.
The news came in the wake of a major disappointment in the development of COVID-19 vaccine candidates. On Tuesday night, AstraZeneca said it had to pause its trial of its vaccine, AZD1222, after one participant suffered an inflammatory spinal cord condition called transverse myelitis. Some analysts predicted the setback could result in Pfizer and other rivals claiming a bigger chunk of the eventual market.
AstraZeneca’s vaccine relies upon an adenovirus vector to prompt an immune response against COVID-19, as do candidates from CanSino Biologics and Johnson & Johnson. Vaccines being developed by Moderna and Pfizer and BioNTech use mRNA to generate the immune response. Adenovirus vaccines have more of a track record, leading some analysts to predict earlier this summer that they could have an edge over mRNA vaccines. But that was before yesterday’s hold.
In July, scientists at Beth Israel Deaconess Medical Center who are working with J&J on its vaccine effort released preclinical data showing that a single dose of the company’s lead candidate, Ad26.COV2.S, generated high amounts of COVID-19 neutralizing antibodies in nonhuman primates. The company was preparing to enroll 60,000 people in a clinical trial of the vaccine starting this month.
Pfizer and BioNTech said the new animal data was the basis for the current global phase 2/3 efficacy trial of BNT162b2, which has enrolled over 25,000 people in three countries, with three additional countries starting up soon.