Pfizer, one of the front-runners in the quest for a COVID-19 vaccine, said its candidate vaccine looks safe, and the company expects to have data next month on how well it protects people against the coronavirus.

Pfizer CEO Albert Bourla said Tuesday that he is intentionally revealing more information about the COVID-19 candidate vaccine than he would about any other vaccine under development, because he wants the process to be open and transparent.

“Transparency is a must, particularly given this situation and the politicization of the vaccine,” he said in a Q&A with journalists.

The company said Saturday that it was expanding its trial from 30,000 to 44,000 people to include teenagers, ages 16-18, as well as people with diseases such as HIV and hepatitis A, B or C. Tuesday, Bourla said the expansion took place because the vaccine appeared to be extremely safe, and the trial could be expanded without delaying the timeline for completion.

The first patient enrolled in Pfizer’s COVID-19 vaccine clinical trial at the University of Maryland School of Medicine in Baltimore receives an injection May 4.

In data released Tuesday, the company showed that participants – both younger people and senior citizens – complained of only minor side effects, such as headaches and sore arms. The data included about 6,000 people; some who received the active vaccine and others the placebo. The company – which is developing its vaccine, called BNT162, in collaboration with German vaccine developer BioNTech – does not know which participant got which.

An independent Data Safety Commission does know who got the active vaccine and has been checking regularly to make sure there are no health concerns, Pfizer executives said.

There probably have been some serious health issues during the trial, but the safety panel “concluded that none are vaccine-related,” said Kathrin Jansen, Pfizer senior vice president and head of vaccine research and development.

The larger numbers should allow the company to look more closely at subgroups of participants, such as those with underlying health conditions such as HIV, and those who had the virus when they received the vaccine, she said.

A final report on the safety and effectiveness of the vaccine should be ready for regulators to review next month.

The vaccine must be at least 50% effective – protecting on average at least half the people who take it – for it to win federal approval and be given to the public. Pfizer manufactures BNT162  in three plants in the USA – in Kalamazoo, Michigan; St. Louis; and Andover, Massachusetts – as well as in Germany and Belgium.

It is not clear how long the vaccine’s protection will last. The company is preparing for three possibilities: that people will need an annual shot, as with the flu; that they will need a vaccine every few years, as with tetanus; or that it will be one-and-done, like the polio vaccine, said Dr. Mikael Dolsten, the company’s chief scientific officer.

“We think this vaccine has the potential to give reasonable and good protection, but we need to monitor [it],” Dolsten said. “It’s reasonable also to assume that we need maybe in the future a boost, because this is a real pandemic and there’s going to be a lot of virus circulating even after global [vaccination] campaigns.”

Jansen said that although Pfizer is committed to and “very happy with its current vaccine candidate,” the company is already working on a second generation.

Pfizer hopes to make two improvements in the next generation, she said: eliminating the need to keep the vaccine frozen and altering the technology so only one dose will be needed, instead of two.

BNT162 uses technology called messenger RNA, which trains the person’s cells to make a protein on the surface of the coronavirus that causes COVID-19. Once the immune system learns to recognize this protein, it will attack when it sees it again on the virus.

In a next-generation vaccine, Jansen said, she could envision a messenger RNA that could amplify itself. “There may be an opportunity that with such an approach, you would be able to only need a single shot” that would provide both “the priming and the boosting effect.”

The vaccine needs to be kept frozen at minus-80 degrees, the temperature of dry ice. Pfizer ships BNT162 in coolers that maintain the ultra-cold temperature. The cooler can be fed with dry ice to keep the vaccine frozen for 15 days, then it can be refrigerated for up to five more days before being diluted and injected, said Angela Hwang, president of the Pfizer Biopharmaceuticals Group.

Because the company expects high demand for the vaccine, and its shipping network is efficient, Hwang said the vaccine shouldn’t suffer heat damage. “No dose is going to be lying around for very long,” she said.

A second-generation vaccine that did not require such cold conditions would be an improvement, Dolsten said.

Bourla, speaking at the end of a two-day conference for investors, bemoaned the politicization of COVID-19 vaccine and drug development.

But he said he thinks the pharmaceutical industry is “rising to the occasion” of the pandemic and hopes that will boost the industry’s public image.

“I don’t want to declare any victory, just because we’re going to bring a vaccine or a treatment that works, that we’re going to come back to where we deserve to be, but I think it will be a very good step,” he said. “Then we need to continue doing the right thing.”

He had one concluding thought as he ended the Q&A: “Science will win,” he said.