On May 18, 2020, Moderna, Inc. of Cambridge, Massachusetts announced that it had obtained “positive interim clinical data” from a Phase I human clinical trial of its experimental mRNA-1273 COVID-19 vaccine that began on Mar. 16. The biotechnology company said that eight of the 45 healthy adult volunteer trial subjects developed antibodies that may provide protection from the SARS-CoV-2 virus that causes COVID-19.1 2 3 The company also reported that four participants suffered Grade 3 vaccine reactions.
Moderna’s chief medical officer Tal Zaks, MD said:
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. 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.
Severe Adverse Events Reported After One or Two Vaccine Doses
Each of the 45 participants was given two doses of the Moderna vaccine about a month apart. The dosage levels were 25, 100 or 250 micrograms (µg). Moderna said that the four participants who received doses of 25 µg developed antibodies against SARS-Cov-2 about two weeks after the second dose was administered and that the same was true for the four participants given doses of 100 µg. The company noted that the vaccine was “generally safe and well tolerated.”1 2
The mRNA-1273 vaccine reportedly produced a “Grade 3 adverse event” in one participant among those who received doses of between 25 µg and 100 µg doses. That person experienced Grade 3 erythema or a rash around the injection site. A Grade 3 rash can mean blistering, open ulcers, wet peeling (moist desquamation) or a serious rash over large areas of the body.4 5
Three participants in the clinical trial who received a vaccine dose of 250 µg doses experienced “Grade 3 systemic symptoms” following administration of the second dose. Moderna described these as the “most notable” of the adverse events and said that they had been “transient and self-resolving.”1 2
The U.S. Department of Health and Human Services (HHS) describes a Grade 3 adverse event as “severe or medically significant but not immediately life-threatening; hospitalization or prolongation of hospitalization indicated; disabling; limiting self care” such as “bathing, dressing and undressing, feeding self, using the toilet, taking medications.”6
Moderna said that none of the participants in the clinical trial experienced Grade 4 adverse events. HHS lists grade 4 events as “life-threatening consequences; urgent intervention indicated.” It describes Grade 5 events as “death related to [adverse events].”1 6
All 45 of the participants in Moderna’s Phase I clinical trial were healthy individuals 18 to 55 years of age.