"We don't really know" if a third shot will be the final or if more are needed, Hoge told Yahoo Finance.
In addition, who would benefit most from an additional shot is still a question.
"This is the key scientific question we're all wrestling with now," Hoge said.
If an additional dose does prove to provide some level of increased protection, it would likely be necessary when late fall and winter approach, when respiratory illnesses thrive and breakthrough cases are likely to increase, he noted.
Health experts have been watching the upcoming seasons with dread, anticipating yet another surge in cases nationwide. The severity of those cases could be low considering the higher levels of vaccination, but the Delta variant is proving to be capable of increasing breakthrough cases and other variants could develop and spread by the year's end.
It's why some experts have said that the current level of vaccination is sufficient and the memory cells, whose job it is to remember how to fight off COVID-19 after being trained by the vaccine, should be relied on.
Others however are relying on antibody levels, which are typically highest after a vaccine, in order to determine when to boost.
But Hoge said he disagrees the two are mutually exclusive. "We think ... the debate between whether it's memory cells or antibody titers is a bit false. Both are important," he said.
In data released Wednesday, Moderna showed better protection against breakthrough cases after 8 months from the first dose compared to after a year. But the most benefit will be derived from the elderly and immunocompromised — the latter of which has already received authorization for boosters by the FDA.
Moderna is also seeking authorization for its booster dose, which is 50 micrograms, half the dose of the original shot. It anticipates getting FDA authorization not long after Pfizer (PFE), whose advisory panel hearing is set for September 17.
Manufacturing boost for Moderna
In addition, Moderna is eyeing the potential to increase manufacturing as a result of a lower booster dose. That's an area where, unlike the other vaccine companies, Moderna still lags.
The once-small biotech has seen a boost in the company's stock since arriving on the COVID-19 vaccine scene last year. The surge in available capital is allowing it to increase its manufacturing amid the pandemic but at a slower pace.
"For us as a company, we are flat out in manufacturing," Hoge said.
The company has relied on third parties, known as contract manufacturers, which hasn't been without problems, which is why the company has to focus on expansion while still making good on existing dose commitments.
"We are making as much as we can, and have been for the better part of a year — and will be for the better part of the next year. We are trying to scale up and invest in manufacturing to create more doses," Hoge said.
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