Moderna's COVID-19 Vaccine Clinical Trial Moves into 2nd Round of Dosing


On March 16, Moderna and the National Institute of Allergy & Infectious Diseases (NIAID) began dosing patients with mRNA-1273, its vaccine candidate against COVID-19. The second round of dosing in healthy Seattle volunteers has now begun.

Without placing too much significance on this, it is a good sign, suggesting that the trial is progressing well and there are no obvious bad side effects from the first round.

Lisa Jackson, senior investigator, Kaiser Permanente Washington Health Research Institute, who is heading the study, told USA Today that the physicians at Kaiser Permanente’s Vaccine Treatment and Evaluation Unit in Seattle don’t have results from the first round. This suggests that the study data is blinded, meaning it will not be released until a specific point in the trial.


mRNA-1273 is an mRNA vaccine against SARS-CoV-2 that encodes for a prefusion stabilized form of the Spike (S) protein. The mRNA vaccine is a new type of technology, where the vaccine contains a section of messenger RNA that codes for a protein associated with the virus. The vaccine is injected into a person and the mRNA moves into the test subject’s cells, where the cells then churn out the protein. The body’s immune system should then treat the protein like the virus and attack it, developing an immune response that it will then use if it comes into contact with the actual virus.

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A more traditional vaccine uses either a dead or weakened form of the virus or proteins from the virus.

The Phase I trial is evaluating three doses, 25, 100 and 250 µg administered on a two-dose schedule given 28 days apart. A total of 45 healthy adults are enrolled in the study. They will be followed through 12 months after the second vaccination.

Of the second doses, Jackson said, “The trial hasn’t been stopped. We know from the study protocol that if adverse events had happened, the protocol would have required that. Therefore, we presume those things haven’t happened.”

Which is good news. What is also important, and is unclear at this point, is whether the vaccine is resulting in an immune response, how much of an immune response—will it be enough to offer protection against the virus—and how long that immune response will last.

Jackson noted that the two-dose regimen is because SARS-CoV-2 is a novel virus, meaning nobody has been exposed to it before it appeared in late-fall of 2019. The first dose, she said, “is a primer to set the immune system up, giving it a first look at the virus.”

The second dose supports that initial “first look.”

After the first Seattle group was enrolled, the trial expanded on March 27 with more healthy volunteers at Emory University in Atlanta. The first group included 28 volunteers in Seattle and 17 in Atlanta. The National Institutes of Health (NIH) is expanding the trial to include 60 adults over the age of 56, some in Seattle and Atlanta, with additional patients at the NIH in Bethesda, Maryland.

Phase I trials focus on safety and determining dosage, as well as whether the vaccine produces an immune response. The larger, but still small, Phase II trial is more focused on determining if the vaccine is effective in preventing infection.

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