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A candidate vaccine for Covid-19 developed by the drug maker Moderna appears to generate an immune response similar to the response seen in people who have been infected by the virus and recovered, the company said Monday.

In a Phase 1 trial, eight patients who received two doses of the vaccine at the lowest and middle doses tested — 25 and 100 micrograms — developed neutralizing antibodies to the virus at levels similar to people who had recovered from infection, the company said in a statement.

The data were limited and from only a small number of participants in the trial, led by the National Institute of Allergy and Infectious Diseases. But they are still likely to be seen as encouraging. Research aimed to develop a vaccine against SARS, a related virus responsible for a 2002-2003 outbreak, showed that neutralizing antibodies are pivotal for achieving protection.


Moderna is developing the vaccine in conjunction with the NIAID’s Vaccine Research Center.

“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, Moderna’s chief medical officer.


The statement noted that a new arm of the trial is being established to test a 50-microgram dose, which may suggest concern that the 25-microgram dose may be too low.

As the vaccine’s developers work to establish a dose, they must balance the need to achieve protection in individuals — including seniors, who are at highest risk in this pandemic but whose immune systems do not respond as well to vaccines — with the goal of using as little vaccine as possible per person to stretch out what will be limited supplies.

“I think 25 [micrograms] gets us there but you always want to have somewhat of a margin,” Zaks told STAT in an interview.

“The sense is at the end of the day we’re going to narrow it down on somewhere between 25 and 100,” he said. “It’s going to be really hard math for us.”

While some experts wanted more detail before commenting on the data, others saw it as a positive sign for this vaccine.

“The neutralizing antibody and safety results from the Phase 1 clinical study are promising for the Moderna mRNA vaccine candidate and supportive to proceed forward with the planned Phase 2 studies,” Robin Robinson, chief scientific officer at RenovaCare, told STAT. Robinson is a former director of the Biomedical Advanced Research and Development Authority.

Vaccination with the candidate vaccine, provisionally labeled mRNA-1273, also prevented viral replication in the lungs of mice in preclinical testing, the company’s statement said.

A Phase 2 trial has already been given the go-ahead by the Food and Drug Administration. CEO Stéphane Bancel said the company is pushing forward with a Phase 3 trial set to start in July and is ramping up its capacity to manufacture the vaccine.

“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,” Bancel said, referring to the virus that causes Covid-19.

The company’s statement suggested the vaccine was well-tolerated in people who received it in the Phase 1 dosing trial. One of the people in the 100-microgram arm developed redness at the injection site that met the criteria for a Grade 3 adverse event. And three volunteers in the highest dose arm — 250 micrograms — developed Grade 3 systemic reactions after receiving the second of two doses. There were no Grade 4 or life-threatening adverse events recorded in the trial.

The early readout included arms of the trial involving people ages 18 to 55 years old who received either two doses at the 25 microgram or 100 microgram level or one dose at 250 microgram. There were 45 people involved in these three arms, though neutralizing antibody data are only available at this point for the first four patients each of the 25 microgram and 100 microgram cohorts.

People who received two doses at the 25 microgram level developed binding antibodies at levels consistent with those seen in the blood of people who have recovered from Covid-19 infection, the statement said. People who received two doses at 100 microgram had binding antibody levels that “significantly exceeded” the levels seen in the blood of Covid-19 survivors.

  • Given the robust dose dependent response observed, even in the small sample, bodes well for the efficacy of the vaccine in the sample population of 18 to 55. We will soon get results from all subjects, including seniors. Hence, the enthusiasm for Moderna, and another mRNA vaccine by Pfizer seems justified. Long term efficacy needs to be proven. In the interests of time, two 100ugm seems to be a logical phase 2 dose, depending on the PK data and side effects. The 100ugm has room for reduction to 75 or 50 ugm to reduce side effects.

    • Nazir- Agreed. However, I might add that it’s not even known how long immunity persists after actual infection with the virus, because the virus is so new. Antibody titers in the 100 microgram dose were significantly more than one gets from infections. If Moderna gets 6 or more months that will be quite sufficient for the USA at least, because we can boost again later. (The same couldn’t be said about a vaccine delivered by a viral vector.)

    • Oh, I might add one thing– From the company webcast, it sounded like they were more interested in a reduced dose so that they could produce more doses of vaccines in a hurry. Otherwise, other considerations would argue for a full 100 microgram dose– Since it isn’t known how long immunity to the virus lasts, they’d prefer to have have some margin of safety rather than a minimal dose.

  • Just a co-incidence that just days after appointing his new head of covid19 team, Moderna hits national news touting a possible vaccine & their stock goes thruthe roof? And guess who has stocks/ interests in Moderna? Why, it’s Trump’s new head of response team.

    • And I suppose the Clinton’s, Bidens, Pelosi’s et al do to. So why try to create division and promote hatred in a time when national unity across political lines is what’s needed. Please try to unite people not turn good news into a cause for animosity.

    • Did you also notice that he agreed to donate the stock bump profits to charity after he took the job? My guess is that is the guy who was CEO of a company that is making a top vaccine perhaps may be the best guy to get the vaccine in production and blow out the bureaucracy. But if you want an FDA official in charge, we will be waiting for a few years.

  • This sounds promising but further clarity is required about the virus subtypes. From a hypothetical point of view, can this vaccine generated immune response be generalized to all virus subtypes infections. Are there subtypes that might not be covered by this vaccine?

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