At day 43, following the second dose, levels of binding antibodies in the 25-mcg cohort were at the levels generally seen in blood samples from people who recovered from the disease.
Bancel said the findings of the study, which was led by the National Institutes of Health and has yet to be peer-reviewed, are "interim data" and that "it's a small data set. but, they are encouraging data". The levels of those so-called neutralizing antibodies matched the levels found in patients who had recovered after contracting the virus in the community. Then he reminded investors of a study of two Zika vaccines that were very similar in their ability to generate neutralizing antibodies-but that ended up offering wildly different levels of protection against that virus.
How is the vaccine prepared?
Nevertheless, the lack of precise data from Moderna irked other researchers.
"We've demonstrated that these antibodies, this immune response, can actually block the virus".
A viral protein requires heavy production needs; an mRNA vaccine bypasses that need.
The age of the volunteers that developed "neutralising" antibodies also remained unknown, so there was a risk that it was biased towards younger and healthier individuals.
What does this mean for a vaccine timeline?
The company said that grant will enable it to supply millions of doses per month in 2020 and, with further investments, tens of millions a month in 2021 if the vaccine proves successful.
Moderna announced on May 7 that the Food and Drug Administration, or FDA, has cleared their application to proceed to a clinical trial (phase two) involving about 600 people.
The world grapples with the coronavirus disease, with over 4.89 million people infected with the virus. The initial results are based on tests of the low and medium doses. One patient at a lower dose level experienced redness at the injection site.
The company said that three patients at the highest dose level experienced some discomfort, including fever, after receiving their second dose of the vaccine. A high dose version is being dropped after spurring some short-term side effects.
What's more, using convalescent serum as a benchmark is problematic, particularly because Moderna generated that data internally, Raffat said. A gradual slide in the shares that began when trading opened gained momentum after a report from the health publication Stat highlighted the early nature of the vaccine data, helping to drag down the broader market. However, the shares plunged after health publication Stat News reported that "the vaccine does not provide the critical data needed to assess its effectiveness", Reuters reported. How durable will the response of the vaccine be?
Moderna recently announced a partnership with the giant drugmaker Lonza to boost its manufacturing capacity to up to one billion doses a year.
Zaks said the battle against COVID-19 marked the firm's ninth bid to develop vaccines against viruses, "and we succeeded with the previous eight".