LANDOVER, Maryland - As tens of thousands of his National Guard colleagues descended on the nation's capital to ensure the peaceful transfer of presidential power, 16km up the road, Emmanuel Alfaro was doing what he viewed as the pinnacle of his career in the Guard: administering Covid-19 vaccines to his fellow citizens.

"It's a highlight, being able to come out and help the public out," said Alfaro, a senior airman and medic with the 175th Air National Guard, whose normal duties are helping at health care centres in Maryland.

As the pandemic continues to rage nationwide and a vaccine programme to control it struggles, governors are increasingly turning to the National Guard to help expedite the process. At least 16 states and territories are using Guard members to give shots, drawing on doctors, nurses, medics and others skilled in injections.

Many more states are using thousands more Guard personnel for logistical tasks, like putting together vaccine kits and moving them around, logging in patients and controlling lines at state vaccination sites. In West Virginia, for example, about 100 Guard troops are assisting with distribution across the state.

"We are a logistical operation here," said Major Holli Nelson, a spokesperson for the Guard there. "That is what the military does best." The growing presence of the Guard is a stark reminder that even as the country reels from the attack on the Capitol last week, a pandemic continues to roil all the states, which are struggling to expedite a complex vaccine programme with no modern precedent.

Since January of last year, 1 in 14 people who live in the United States have been infected with the coronavirus, and at least 1 in 862 have died. States like California and Arizona, with some of the highest number of infections in the nation, are contending with exhaustion among health care workers and inundations across their medical centres.

"States are naturally looking at alternative ways to get out the limited supply of vaccines," said Claire Hannan, the executive director of the Association of Immunisation Managers.

"We are seeing more and more states using the National Guard and thinking bigger." In Maryland, Governor Larry Hogan originally planned to disseminate vaccines largely through private health care providers and drugstore chains, setting up state-run health care clinics later.

Last week, realising that the private sector was unable to ramp up operations as quickly as he had hoped, Hogan turned to 140 Maryland National Guard members to help with pop-up sites in two counties and will be adding six more next week to help county and state health officials.

States have struggled to get the roughly 30 million doses of vaccines released by the Trump administration to Americans. The desire for vaccines has greatly outstripped supply, even as some Americans who qualified for an early dose have rejected them, causing the federal government and states to adjust their guidelines on who can receive them first.

Registration websites have crashed. Endless waits on phone lines have frustrated people seeking appointments or simple information. And some private health care centres have been unable to work through bureaucracies to get doses to the right people, at times wasting opened vaccines or giving them to people far down the priority list. In Florida, older residents camped on lawn chairs outside centres waiting for their shots.

State health department officials say they are happy to have the Guard's ability to put up tents in 15 minutes and turn to a bevy of skilled personnel to quickly scale up and change direction when steps like registration are bogged down.

"It was a no-brainer for us," said C.J. Karamargin, a spokesperson for Governor Doug Ducey of Arizona, a state that deployed the Guard immediately after receiving its vaccine supply in December.

"This crisis has seen the largest mobilisation of the Arizona Guard since World War II." The Guard was called on to assist with personal protective equipment and testing, and "they hit it out of the park," Karamargin said.

The federal government currently will reimburse states - many of them struggling from large drops in tax revenues - for only 75 per cent of their National Guard costs associated with coronavirus relief.

At one point, the Trump administration gave 100 per cent reimbursements to Florida and Texas, and governments from both parties say they intend to press the Biden administration to make whole on this front.

"North Carolina has been clear we would like to get to 100 per cent reimbursement," said Sadie Weiner a spokesperson for Governor Roy Cooper. On Monday, the state's first teams of 75 Guard personnel in two cities began to "stick, plunge and pull," said Lt-Col Matt DeVivo, a spokesperson for the Guard. They expect to greatly increase their sites over the next few weeks.

Some heath care experts were sceptical that the Guard could keep up when vaccine allotments became larger.

"All hands on deck are important," said Dr Georges C. Benjamin, the executive director of the American Public Health Association. "But I think you have to be realistic, though, about the Guard's ability. We have to be careful that we are not expecting them to bring more medical assets than they can to the table. Guard members are working in hospitals and pharmacies already detailed to provide services for Covid-19." Guard officials say they have the capacity to manage the need.

While the Defence Department has frequently boasted about its role in Operation Warp Speed, the federal vaccine effort, Pentagon officials have said that active-duty troops would not be administering shots.

Further, many officials are mindful of a history of the United States conducting unethical medical experiments on Black Americans and general distrust of government. Having uniformed Guard troops give shots was something that could require extra assurances, officials said.

"I do think that is something we really need to pay attention to," said Hannan of the Association of Immunisation Managers. "I don't know if we understand all the questions around that. But the trust and confidence in the vaccine is in a different place than it was in July and August, when there were strong concerns about the military delivering the vaccine."

This week, uniformed Guard troops wove among state and local health officials around the sporting centre in Landover to get to about a dozen white tents to give residents - largely emergency medical workers - their shots.

Taylor Brown, an official with the Office of Emergency Management in Prince George's County, Maryland, looked on with approval; the county has been one of the hardest hit in the state.

"Thank goodness they are here," she said. "The more the merrier, really."