Some of the same problems that have plagued the coronavirus vaccine rollout could also make it harder for people to get the second dose of the vaccines.

Why it matters: The two vaccines authorized so far both require two shots to reach the full potential of their protection, and those second shots need to happen within a specific window of time —putting extra pressure on a system that’s already struggling to work out its kinks.

What's next: This week will be“when we’re really starting to scale up to the second dose..the challenge is going to be about the availability of inventory and scheduling,” Louisville Mayor Greg Fischer said in an interview.

• “Unlike the first dose, you’ve gotta get the second dose within that time window, so there’s a little more criticality to it,” he added.

The problem: Some states say they don’t have enough visibility into how many doses of vaccine they are getting from the federal government, and when.

• “You need to have information on that entire supply chain,” said Celine Gounder, a professor at NYU Grossman School of Medicine. “Forget second doses, we just don’t know where doses are.”
• “You need to have visibility three to four weeks in advance to make sure you have that dose in hand, on time, for those patients who are coming back for a second dose,” said Jessica Daley, a vice president at Premier Inc., which works with health systems across the country.

Between the lines: When vaccinating health system employees, “we know them, we can account for them, and it’s a finite number. But when it gets to the community, its magnitude is multiple, multiple times” that, said Scott Evans, CEO of Sharp Grossmont Hospital.

Where it stands: Nationally, about 8% of the population has received at least one dose of the vaccine, and less 2% have received both shots, per Bloomberg.

• The Biden administration isn't holding doses in reserve for people's second shots — it's shipping everything it can right away, trying to give as many people as possible at least some protection. Second doses will come from new supplies, although some providers and health departments are withholding second doses themselves.
• Once someone receives the first dose of the vaccine, they have six weeks to get the second, per the Centers for Disease Control and Prevention’s recommendations.

Scheduling is also an issue. States and localities that used Eventbrite or other first-come, first-served systems may not have an easy way to guarantee appointments for second doses.

• “Things as simple as making appointments and calling people to come back and remind them to take their second dose — we don’t have the infrastructure," Gounder said.

The other side: Some health officials and providers feel confident that they’ll be able to make the second dose process run smoothly.

• This often comes down to being able to successfully pull off the little things, like differentiating online between first dose appointments and second dose appointments or scheduling second dose appointments at the same time patients receive their first dose.

The bottom line: We don’t know what will happen if millions of Americans fail to receive their second shot in a timely manner. But at this point in the pandemic, we can little afford to figure it out the hard way.