“I don’t think the current situation demands a multitrillion-dollar package,” Senate Majority Leader Mitch McConnell told reporters on Tuesday. “So I think it should be highly targeted, very similar to what I put on the floor in both October and September.” That would likely match the size of the $500 billion “skinny” stimulus package that was blocked twice by Senate Democrats this fall. But a more modest stimulus package means some items could get left out altogether. Indeed, Senate Republicans’ plans have excluded another round of $1,200 stimulus checks from the package—an item both the White House and House Democrats have supported for months.

Last week House Speaker Nancy Pelosi told reporters a smaller bill “doesn’t appeal” to her, reiterating her stance that the Senate Republicans’ “skinny” bill was a nonstarter for Democrats.

But McConnell taking the reins for Republicans in stimulus negotiations isn’t the only hurdle facing stimulus checks.

Vaccine hopes could ‘delay’ a package

Another reason more stimulus may be pushed back? An encouraging report from Pfizer and BioNTech on the efficacy of their COVID-19 vaccine, currently in late-stage trials. The vaccine would be great news for the country—but potentially bad news for stimulus talks.

“I worry that for those in Congress who were already squeamish about passing a large stimulus bill, this might encourage them to delay a little bit longer or to pass something smaller because it is good news,” Eric Winograd, senior economist at AllianceBernstein, tells Fortune. “That prospect might encourage a smaller bill, which I don’t think would be the right policy choice.” (He believes $1.5 trillion would better serve the recovery.)

The problem, Winograd notes, is that the promise of a vaccine “a few months from now“ doesn’t help the more than 11.1 million Americans who are currently unemployed. And the latest vaccine developments don’t change the “urgency” for stimulus to renew those expiring benefits.

Tom Porcelli, chief U.S. economist at RBC Capital Markets, doesn’t necessarily think there needs to be a multitrillion-dollar package (he believes something around $700 billion may suffice as a “bridge”), but agrees the vaccine “takes some of the edge off the urgency with getting it done sooner than later.”

Stimulus checks are a ‘lower priority’

Notwithstanding the vaccine, some economists note a stimulus check might not be in the cards at all, even if a package is passed.

“I think [more stimulus checks are] going to be a very hard sell. If you have a Republican Senate, I think that’s almost a nonstarter,” RBC’s Porcelli tells Fortune, referring to the future balance of power if Republicans secure two runoff Senate seats in Georgia come January. AllianceBernstein’s Winograd on the other hand argues that nothing “is off the table, because who really knows? But I would think that is a lower priority item than is extending unemployment benefits.”

Meanwhile, stimulus checks aren’t high up on some economists’ wish lists for the next bill, either: Porcelli, Winograd, and UBS Global Wealth Management senior economist Brian Rose all agree more enhanced unemployment benefits and small-business Paycheck Protection Program loans are more important to aiding the most affected groups.

A lame-duck deal?

While there is broad consensus among most economists that more aid is needed—and soon—getting a deal passed in the lame-duck session before 2021 is looking like a tall order.

To be sure, it’s not impossible a deal could get done in the lame duck, as those like McConnell have even recently said a deal needs to be done “before the end of the year.” But Pelosi thus far doesn’t seem willing to capitulate on the size and key sticking points, and neither does McConnell.

Indeed, Sen. Roy Blunt (R-Mo.) outlined it Monday: “Both sides are saying they want one. But both sides are saying they want the one they want. So we’ll see.”

According to RBC’s Porcelli: “The direction that it goes, and the person that will ultimately end up getting what they want, is going to be entirely contingent on the virus. I think the urgency will rise if case counts really do start to advance from here in a more dramatic way.”

Many economists agree a deal in the lame duck would be smaller than iterations of the bill discussed leading up to the election, but if a deal does get pushed until next year, its passage is largely dependent on the composition of Congress.

If Congress is split and Republicans maintain control of the Senate (a scenario many find most likely), Winograd finds it “hard to believe that Republicans in the Senate who were not eager to pass a stimulus bill in the midst of an electoral campaign would be willing to do so in the early days of a Democratic administration.”

But if Democrats win the two runoff seats in Georgia and clinch control of both the House and Senate, some economists believe that could mean a bigger deal early next year and possibly follow-up stimulus legislation later in the year.