Facing record levels of coronavirus, the United States began shipping vaccine nationwide on Sunday as it launched a massive immunization effort, while in Germany an explosion of cases forced a return to partial lockdown.

Delivery trucks with special refrigeration equipment rolled out of a facility in Kalamazoo, Michigan, as part of a public-private plan to ship millions of doses of the newly approved Pfizer-BioNtech vaccine to vulnerable Americans.

Delivery services FedEx and UPS are deploying fleets of trucks and planes to carry their precious cargo — sometimes under armed guard — to all 50 states, where healthcare workers and nursing-home residents will be first in line. 

As the historical mobilization unfolds, an initial 2.9 million doses are to be delivered by Wednesday, with officials saying 20 million Americans could receive the two-shot regimen by year end, and 100 million by March.

One state governor, Andy Beshear of Kentucky, tweeted Sunday, “We now believe that the first individuals will be vaccinated” on Monday morning — less than 72 hours after the vaccine received emergency authorization from the US Food and Drug Administration.

But the breakthrough comes at one of the darkest moments of the global pandemic, with infections in the United States and many other countries soaring and health experts still struggling against vaccine skepticism, lockdown fatigue and uneven adherence to safety rules.