Pharmaceutical giant Pfizer reported no major safety problems on their COVID-19 vaccine trial after more than 12,000 people received their second of two doses.

During an online meeting with investors, Mikael Dolsten, Pfizer's chief scientific officer, said there has been "no safety signal reported" so far.

The trial has reached its initial goal of 30,000 subjects. It is now targeting at enrolling 44,000 people, according to Pfizer executives. The company has expanded its trial to include teenagers and people with certain medical conditions, such as HIV.

The trial compares two shots of the vaccine Pfizer is co-developing with Germany's BioNTech SE to two doses of a placebo. The doctors and subjects in the trial do not know who got the vaccine, which is a measure to avoid bias.

A committee of outside experts who know which people received the shot is reviewing safety data weekly, said Pfizer executives.

Kathrin Jansen, Pfizer's head of vaccine research, noted that they would be notified if these people had any safety concerns. She said the review team had not done that as of the moment.

Meanwhile, Pfizer's own scientists are looking for worrisome adverse events that have not appeared so far. Fatigue has been one of the most common side effects seen in the trial so far.

Pfizer also said that it expects to get conclusive data on the vaccine's efficacy by the end of October. The board responsible for the trial will do its first review of the data for efficacy when a total of 32 coronavirus cases have been reported among participants.

Pfizer also vowed to make its safety and efficacy data publicly available once they start seeking for an emergency authorization for the COVID-19 vaccine.

"What we are doing in terms of releasing data is very unusual. It is a must to release this data," Chief Executive Officer Albert Bourla said in a report.

The safety of the COVID-19 vaccines in the trial has been a huge concern after AstraZeneca paused its clinical trials of the vaccine co-developing with the University of Oxford.

AstraZeneca's U.K. has been continued, but its U.S. trial remains postponed. Once a preliminary analysis of Pfizer and BioNTech's vaccine data shows that it is safe, the companies could seek Food and Drug Administration's emergency authorization.

Jansen said the trial is designed to continue gathering safety and efficacy data even if an emergency authorization is granted. Top executives promised that distribution would immediately start once Pfizer receives an emergency authorization.

Pfizer's president of biopharmaceuticals, Angela Hwang, said there are currently three options for distributing the COVID-19 vaccine.

Distribution can be done with Pfizer's freezer, where the COVID-19 vaccine can have a shelf-life by six months.

On the other hand, Pfizer's COVID-19 vaccine can have a 15-day shelf-life with the company's thermal shippers and dry ice. For a typical refrigerator, the vaccine can last for five days.

Hwang said these different options give a wide range of flexibility. But Pfizer's researchers are already looking for ways to make an improved version of the COVID-19 vaccine.

The company is looking for a new COVID-19 vaccine formula, which could be done in a single dose.

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