Moderna, the Massachusetts biotechnology company behind a leading effort to create a coronavirus vaccine, announced promising early results from its first human safety tests Monday. The company plans to launch a large clinical trial in July aimed at showing whether the vaccine works.

The company reported that in eight patients who had been followed for a month and a half, the vaccine at low and medium doses triggered blood levels of virus-fighting antibodies that were similar to or greater than those found in patients who recovered. That would suggest, but doesn’t prove, that it triggers some level of immunity. The antibody-rich blood plasma donated by patients who have recovered is separately being tested to determine whether it is an effective therapy or preventive measure for covid-19.

Moderna’s announcement comes days after one of its directors, Moncef Slaoui, stepped down from the board to become chief scientist for Operation Warp Speed, a White House initiative to speed up vaccine development. Watchdogs called out Slaoui’s apparent conflict of interest. Filings with the Securities and Exchange Commission show Slaoui’s stock options in Moderna are worth more than $10 million with the company’s share price at $66.69. In pre-market trading Monday, Moderna’s stock soared as high as 30%, to nearly $87.

Moderna also received $483 million from the Biomedical Advanced Research and Development Authority, a federal agency.

“Slaoui’s blatant financial conflicts of interest disqualify him for the role of vaccine czar, unless he commits immediately to global vaccine access conditions over the obvious profit interests of the corporations he serves,” said Peter Maybarduk, director of the Access to Medicines Program at Public Citizen, a consumer advocacy group.

Sen. Elizabeth Warren, D-Mass., called for Slaoui to divest his stock options, tweeting it is “a huge conflict of interest for the White House’s new vaccine czar to own $10 million of stock in a company receiving government funding to develop a covid-19 vaccine.”

The data released Monday by Moderna is encouraging, but represents only a first step in a long process to bring a vaccine to market. It comes from an interim report on dozens of patients followed over weeks, whereas vaccine studies require broad testing in thousands of patients followed over many months or years.

Paul Offit, a vaccine expert at the Children’s Hospital of Philadelphia, said the data looked promising and it made sense to proceed to a large trial this summer.

“The fact that the vaccine elicited neutralizing antibody amounts comparable or higher to those found in convalescent sera [plasma] is very encouraging,” said Arturo Casadevall, chair of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, who is spearheading the initiative to test plasma as a treatment.

Peter Jay Hotez, who is working on developing a coronavirus vaccine at the Baylor College of Medicine, said it would be important to understand the level of antibodies detected in the patients beyond the information provided in a company news release. He pointed to emerging evidence that many recovered patients do not muster high levels after they recover – and that high levels of antibodies are needed to neutralize the virus.

The vaccine showed no worrisome safety signals, aside from redness at the injection site for one patient and some transient “systemic” symptoms in three patients given the highest dose, the company said.

The interim data comes from a clinical trial aimed at showing the safety of its experimental vaccine and helping the company select the correct dose. The company has not yet picked the final dose, or announced the size or length of the large trial that it will start in July, which will be the key one that regulators consider to decide whether the vaccine is safe and effective.

“We are very, very happy because first the vaccine was generally safe,” Stephane Bancel, chief executive of Moderna said in an interview. “The piece that was really exciting and was the big question, of course, was can you find antibodies in people in enough quantities” to prevent disease.

Moderna also reported that the vaccine protected mice who were vaccinated and then exposed to the virus, preventing it from multiplying in their lungs. The animal and human data being released by the company have not yet been published.

Moderna’s vaccine uses a genetic material called messenger RNA that codes for the distinctive spike protein that studs the outside of the novel coronavirus. The vaccine delivers the messenger RNA to cells, which then follows the genetic instructions to create the virus protein – allowing the body to learn to recognize and neutralize the pathogen.