Pfizer said yesterday that it expects to sell nearly $34 billion worth of coronavirus vaccines this year — and there could be billions more behind that, if people who have gotten the shot ultimately need boosters.

Why it matters: It's unclear whether, when and for whom a coronavirus vaccine booster will be necessary. Pfizer has a lot of money riding on those answers, and executives are already making the case that many Americans will need a third dose.

What they're saying: Pfizer released new data, not yet peer-reviewed, that suggests the vaccine's efficacy diminishes over time — from 96% in the first two months after receiving the second dose, to 84% after four months.

• Reduced efficacy could mean more transmission of the virus.
• "We are very, very confident a third dose, a booster, will take up the immune response to levels that will be enough to protect against the Delta variant," Pfizer CEO Albert Bourla told CNBC yesterday.

Yes, but: The same data show the vaccine was still 97% effective in preventing severe disease, across a full six months of monitoring.

• Those findings reinforce the FDA and CDC stances that people may not need booster shots at this time.

By the numbers: Pfizer increased its sales estimates yesterday for the doses it has already committed to sell. The company expects those sales to total $33.5 billion this year, almost a 30% jump from its previous estimates — without accounting for sales of any potential boosters.

What's next: "The [vaccine sales] numbers are going to be much higher," Bernstein analyst Ronny Gal wrote to investors, estimating Pfizer's sales could be as high as $43 billion this year.

• "We expect total sales growth will slow over the next 12 months as COVID-19 vaccine demand shifts toward emerging markets where pricing is lower," analysts at Morningstar wrote about Pfizer. However, "potential upside exists if larger demand for boosters emerges."