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Leaders from the two companies responsible for America's most-used COVID-19 vaccines looked back Saturday at how they were able to develop the lifesaving shots so quickly – and offered a glimpse of what might lie ahead in the fight against the coronavirus and other maladies.

Dr. Mikael Dolsten, chief scientific officer at Pfizer who oversees its worldwide research, and Stéphane Bancel, Moderna's chief executive officer, spoke at the ÃÛÑ¿´«Ã½'s virtual Scientific Sessions.

Dolsten said that from the start of the pandemic, Pfizer was planning not just for the immediate challenge of developing a vaccine that worked, but for everything that would follow. "We really tried to take a holistic, comprehensive approach," with "end-to-end planning."

Vaccine developers usually wait for one step of the development process to conclude before moving on to the next. "But this was a pandemic," he said.

So as soon as the company had promising data from early tests, it was setting up advanced clinical trials and preparing for manufacturing.

The approach of "working in parallel, rather than serial" paid off, Dolsten said. Not only is the company on track to deliver up to 3 billion doses of its vaccine by year's end, it promising results for an antiviral COVID-19 pill.

The process was always about finding "maximum benefit and the best safety profile," he said.

Moderna's Bancel echoed that emphasis on safety.

"The thing that was always our North Star was to never take any risk to a clinical trial participant," whom he called "the unsung heroes of the pandemic, like the health care workers, of course."

Like Pfizer, Moderna was able to do "everything in parallel, as long as it was safe. That was of course the No. 1 criteria. But we took a lot of business risks."

Those, too, paid off. Moderna, as a company, made less than 100,000 doses of any vaccine in all of 2019, he said. It is on track to ship up to 800 million doses this year.

He and Dolsten both foresee a long-lasting role for their products. "Because unfortunately, we think we're going to need more boosters," Bancel said. "COVID is going to become endemic. It's not going away."

Dolsten expects such vaccine boosters to be annual. The effectiveness of a third shot has been impressive in studies, he said. "Projections are that an annual vaccination is likely going to be very helpful to refill your immune response defense line, and to further train it for any future needs," although those needs might be different for people in high-risk groups, such as people with cancer or cardiovascular conditions.

Bancel envisions a single annual shot that would combine a COVID-19 booster; a flu vaccine that has "a much higher efficacy than what we have seen so far in older-technology vaccines;" and a vaccine for RSV, or respiratory syncytial virus, an illness that's common but sometimes severe in children younger than 2.

"So one shot and you'll be set for the fall and winter," he said.

Beyond COVID-19, both men saw exciting potential in the technology behind their companies' vaccines, which use a molecule called messenger RNA, or mRNA, to deliver information that allows cells to make proteins.

With traditional technologies, the majority of promising drugs don't make it from the lab to market, Bancel said. "We think mRNA is going to change that in a very profound way," because the chemistry and process in mRNA technology is the same for all cell types.

"Once you get the mRNA inside the cells, you can make any protein you want," or combinations of proteins, he said.

Researchers are exploring mRNA treatments that might repair blood vessels harmed by diabetes, treat heart failure or repair damage from heart attacks. Moderna also is testing a vaccine for cytomegalovirus, or CMV, which sometimes causes long-term health problems such as hearing loss in babies whose mothers are infected.

As part of Saturday's presentation, Dr. Biykem Bozkurt, professor of medicine at Baylor College of Medicine in Houston, summarized findings on COVID-19 vaccines and myocarditis, an inflammation of the heart muscle.

Bozkurt was lead author of a study published in July in the AHA journal that looked at myocarditis and COVID-19 vaccines and concluded that the "the risk of hospitalization, ICU stay and death with COVID infection itself far outweighs the risk of myocarditis following mRNA COVID vaccination," she said.

She noted a recent study in the , based on a national database from Israel, estimated the risk of myocarditis at one to five cases per 100,000 people vaccinated. The risk of myocarditis from a COVID-19 infection was much higher, she said, and infection also raised the risk of other problems, including heart attacks.

The risk of myocarditis after vaccination is slightly higher in young males. But overall, cases tend to be mild and resolve in four or five days, she said.

She asked whether the pharmaceutical companies would be willing to partner with others on finding the mechanisms that underlie the problem to potentially adjust the vaccines to reduce or silence those mechanisms. Both leaders agreed.

"Once we know the mechanistic understanding, there could be tweaks that allow us for the future to do even more sophisticated design," Dolsten said, "whether we speak about COVID or future viral challenges."

Find more news from Scientific Sessions.

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