A COVID-19 vaccine candidate under development by pharma giant Pfizer and biotech firm BioNTech showed promise in interim results released Wednesday.

The vaccine candidate, BNT162b1, was able to induce the formation of antibodies that neutralized SARS-CoV-2, the virus that causes COVID-19, in all participants who received doses between 10ug to 30ug, according to a report posted on the preprint server MedRxiv. The report has not yet been peer-reviewed.

Seven days after the last injection, levels of neutralizing antibodies in those who received 10 µg and 30 µg of the vaccine 21 days apart were 1.8 to 2.8 times the level of neutralizing antibodies in recovered COVID-19 patients. 

“These preliminary data are encouraging in that they provide an initial signal that BNT162b1 targeting the RBD SARS-CoV-2 is able to produce neutralizing antibody responses in humans at or above the levels observed in convalescent sera – and that it does so at relatively low dose levels. We look forward to providing further data updates on BNT162b1,” said Ugur Sahin, M.D., CEO and Co-founder of BioNTech, in a press release.

The study placed 45 healthy volunteers between the ages of 18 to 55 into three groups for the initial analysis. Some 24 subjects received two injections of 10 µg and 30 µg, 12 subjects received a single injection of 100 µg, and 9 subjects received 2 doses of placebo control. However, the study did not include results from adults over 65 years of age and pregnant women. 

Three-quarters of the subjects in the first group experienced acute low-grade fever below 100 degrees Celsius, and some experienced minor to moderate pain at the injection site.

More trials must be done in order to test whether the vaccine can lower the likelihood of infection by 50%. But the preliminary results indicate that Phase ⅔ trials may be set to start in late July, as Pfizer Chief Executive Officer Albert Bourla told reporters in May. These trials may enroll up to 30,000 healthy volunteers

The Pfizer vaccine is one of 14 candidates currently in human trials. It is based on messenger RNA, a single-stranded construct that carries a blueprint for a protein immune cells can then learn to attack, the same model as the Moderna vaccine candidate.  

The Moderna vaccine also showed promising early results, inducing neutralizing antibodies in a small group of early volunteers, but further results have yet to be released.

Image Credits: Pfizer, Pfizer.