In desperate times, there are many ways to stretch vaccines and speed up inoculation campaigns, said experts who have done it.

Splitting doses, delaying second shots and employing roving vaccination teams have all saved lives under certain circumstances. During cholera outbreaks in war zones, Doctors Without Borders even used "takeaway" vaccination, in which the recipient is given the first dose and given the second to self-administer later.

Unfortunately, experts said, it would be difficult to try most of those techniques in the U.S. right now. The new mRNA-based coronavirus vaccines approved thus far are too fragile and more complicated to administer than older vaccines, experts said.

There are two strategies that might work with the current vaccines, but each is controversial.

The first is being tried in Britain. In December, faced with an explosive outbreak, chief medical officers said they would roll out all of the vaccines they had, giving modest protection to as many Britons as possible. Early data from the first 600,000 injections in Israel suggest that even one dose of the Pfizer vaccine cut the risk of infection by about 50%.

But some virus experts said single doses could lead to vaccine-resistant strains. Moncef Slaoui, chief scientific adviser to Operation Warp Speed, also warned that single doses might inadequately "prime" the immune system; then, if those vaccine recipients were later infected, some might do worse than if they had not been vaccinated at all.

As an alternative, he proposed using half-doses of the Moderna vaccine. During Moderna's early trials, the 50-microgram vaccine dose produced an immune response virtually identical to the 100-microgram one.

Moderna chose the higher dose to be extra sure it would work; company scientists at the time had no idea that their product would prove 95% effective. So Slaoui suggested using the lower dose.

Many experts also disagreed with that strategy. Dr. Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia, said, "There are no efficacy data on a partial dose."

What the U.S. can and must do now, health experts said, is train more vaccinators, coordinate delivery and get better at logistics.

Thanks to battles against polio, measles and Ebola, some of the poorest countries do better vaccination drives than the U.S., said Emily Bancroft, president of VillageReach, a logistics and communications contractor working in Mozambique, Malawi and the Democratic Republic of Congo and also assisting Seattle's vaccine drive.

"Hospitals here don't even know what they have on their shelves," she said. "For routine immunization, getting information once a month is OK. In an epidemic, it's not OK."

Training can be done on "injection pads" that resemble human arms. And data collection must be set up so that every team can report on a cellphone and it all flows to a national dashboard. "The U.S. will get there," Bancroft said. "The rockiness we're seeing now is the lack of experience."