Promising Results in Early Stages of COVID-19 Vaccine Development

The elephant in the room when discussing a COVID-19 vaccine is whether it is even possible for humans to develop a robust antiviral immune response to SARS-CoV-2.  New research now suggests it is, and preliminary results from an early stage study of one candidate vaccine indicates that the response is similar to that in patients who have recovered from the infection. Here are more details.

CAMBRIDGE, MA – If promising first results for a candidate vaccine for COVID-19 bear out, pharmacists might be administering novel coronavirus immunization somewhat sooner – and with more certainty about effectiveness -- than previously anticipated.

The vaccine from the biotechnology company Moderna appears to generate an immune response in line with that of patients who have recovered from the virus, according to a company press release. 

The company notes that immunogenicity data were currently available only for the 25 µg and 100 µg dose level (ages 18-55) after two doses (day 43) and at the 250 µg level (ages 18-55) after one dose (day 29).

In the National Institute of Allergy and Infectious Diseases-led study, results indicate that all participants ages 18-55, 15 per cohort, across all three dose levels seroconverted by day 15 after a single dose. “At day 43, two weeks following the second dose, at the 25 µg dose level (n=15), levels of binding antibodies were at the levels seen in convalescent sera (blood samples from people who have recovered from COVID-19) tested in the same assay,” according to the press release. “At day 43, at the 100 µg dose level (n=10), levels of binding antibodies significantly exceeded the levels seen in convalescent sera. Samples are not yet available for remaining participants.”

At the time of the announcement on May 18, neutralizing antibody data were available only for the first four participants in each of the 25 µg and 100 µg dose level cohorts. The vaccine, mRNA-1273, was found to be generally safe and well tolerated, with a safety profile consistent with that seen in prior Moderna infectious disease vaccine clinical studies. One participant experienced redness around the injection site.

Meanwhile, preclinical results from a viral challenge study in mice conducted in collaboration with NIAID and its academic partners suggest that vaccination with mRNA-1273 prevented viral replication in the lungs of animals challenged with SARS-CoV-2. “Neutralizing titers in Phase 1 clinical trial participants at the 25 µg and 100 µg dose levels were consistent with neutralizing titers that were protective in the mouse challenge model,” according to the announcement.

“These interim Phase 1 data, while early, demonstrate that vaccination with mRNA-1273 elicits an immune response of the magnitude caused by natural infection starting with a dose as low as 25 µg,” said Tal Zaks, MD, PhD, Chief Medical Officer at Moderna. “When combined with the success in preventing viral replication in the lungs of a pre-clinical challenge model at a dose that elicited similar levels of neutralizing antibodies, these data substantiate our belief that mRNA-1273 has the potential to prevent COVID-19 disease and advance our ability to select a dose for pivotal trials.”

Based on the interim Phase 1 data, the Moderna-led Phase 2 study will be amended to study two dose levels, 50 µg and 100 µg, with the goal of settling on a dosage for pivotal studies. Moderna says it anticipates the dose for the Phase 3 study to be between 25 µg and 100 µg and expects Phase 3 trial initiation in July, subject to finalization of the clinical trial protocol.

“With today’s positive interim Phase 1 data and the positive data in the mouse challenge model, the Moderna team continues to focus on moving as fast as safely possible to start our pivotal Phase 3 study in July and, if successful, file a BLA,” said Stéphane Bancel, Chief Executive Officer at Moderna. “We are investing to scale up manufacturing so we can maximize the number of doses we can produce to help protect as many people as we can from SARS-CoV-2.”

Another NIAID-supported study documented a robust antiviral immune response to SARS-CoV-2 in a group of 20 adults who had recovered from COVID-19. The findings show that the body's immune system is able to recognize SARS-CoV-2 in many ways, resolving concerns that the virus may elude ongoing efforts to create an effective vaccine.

In response to concerns about whether the human immune system can mount a substantial and lasting response to SARS-CoV-2, the study posted online by the journal Cell demonstrates a substantial antiviral immune response to SARS-CoV-2 in a group of 20 adults who had recovered from COVID-19. Supporting efforts to protect against the virus by use of a vaccine, the results indicate that the body's immune system is able to recognize SARS-CoV-2 in many ways.

"If we had seen only marginal immune responses, we would have been concerned," explained Alessandro Sette, Dr. Biol. Sci., at La Jolla Institute for Immunology’s Center for Infectious Disease and Vaccine Research, and adds, "but what we see is a very robust T cell response against the spike protein, which is the target of most ongoing COVID-19 efforts, as well as other viral proteins. These findings are really good news for vaccine development."

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