The first company in the US to begin human testing for a coronavirus vaccine has reported “positive results” from the initial tests.

The biotech company, Moderna, previously dosed 45 patients between the ages of 18 and 55 with varying doses of its experimental drug.

In 25 people who received either the 25mg or 100mg measure doses of the experimental vaccine, levels of antibodies reached or exceeded levels found in patients who had fought of Covid-19, according to a company statement.

“This is a very good sign that we make an antibody that can stop the virus from replicating,” Moderna Chief Executive Officer Stephane Bancel told Bloomberg in an interview.

The data “couldn’t have been better,” he said.

In all eight people examined in the second round of testing, the vaccine caused people to create enough antibodies to defeat the virus in a test tube.

“These data substantiate our belief that mRNA-1273 has the potential to prevent Covid-19 disease,” Tal Zaks, Moderna chief medical officer, told The Financial Times.

Three patients who received a high dose of the vaccine had more severe side effects, the company said. As a result, researchers have ruled out the use of this dose in later trials.

One person who received the middle dose experience more severe side effects, but all of the symptoms were temporary and resolved themselves on their own, the statement said.

In light of the findings the company has said the experimental vaccine is thought to be “generally safe and well-tolerated”.

The next phase of the trial, which will see the company will administer the vaccine to 600 patients, is set to begin shortly.

The third trial will need to include thousands of participants, to demonstrate safety and efficacy across a large number of the population.

The coronavirus has infected more than 4.7 million people and killed over 300,000, according to data from the Johns Hopkins University.

A successful vaccine has previously been considered the only real “way out” of the coronavirus pandemic, allowing countries to re-open economies. Around a dozen experimental vaccines are in the first stages of testing or nearing it worldwide.

Moderna’s results are just a sample from the small, first study of many needed to make ensure a vaccine is viable, and experts say initial results should be viewed with caution.​