Johnson & Johnson said it is sending additional experts to oversee production of its COVID-19 vaccine at a plant in Maryland where human error ruined millions of its one-dose vaccines. The plant is owned by a company that reportedly has been cited by US health officials for quality-control problems.

Emergent, a contract manufacturer based in Gaithersburg, Maryland, has been making the main ingredient for the pharmaceutical company's vaccine at one of its plants in Baltimore known as Bayview.

Workers at the plant mixed up the ingredients in the vaccine, The New York Times reported Wednesday. J&J didn't disclose the nature of the lapse in quality or how many doses were affected, but the Times said 15 million doses were ruined. J&J said the doses weren't distributed.

Emergent is one of about 10 companies J&J is using to speed up manufacturing of its recently approved vaccine, the New Brunswick, New Jersey-based company said. Emergent has been cited repeatedly by the Food and Drug Administration (FDA) for problems, according to records obtained by The Associated Press through the Freedom of Information Act. The records cover inspections at Emergent facilities since 2017.

The Washington Post reported that workers at the Baltimore plant in late February mixed up the ingredients for the AstraZeneca and J&J vaccines both being produced there, throwing the entire batch into question.

The FDA had previously flagged quality-control concerns at the plant related to its testing of a potential treatment for anthrax, according to the AP.

The Bayview factory where the tainted vaccine ingredient was found hadn't yet been approved by the FDA, so no vaccine in circulation is affected. Emergent declined to comment.

Future shipments of the J&J vaccine have been halted while the FDA investigates, the Times reported. The FDA said it was aware of the situation but declined further comment.

Doses of the J&J vaccine that already have been distributed aren't affected because they were made in the Netherlands, according to the Times. J&J said it would be able to make enough doses to meet production targets for the US in the coming months.

The J&J vaccine is one of three being used in the United States. Pfizer and Moderna vaccines were already the bulk of the US supply, and the manufacture of those is proceeding as planned.

The problems with J&J's manufacturing process came less than a week after President Joe Biden doubled his target for the number of shots to be administered during his first 100 days in office, to 200 million.

As of Wednesday, more than 150 million shots had been administered in the US — including 3.3 million J&J jabs, according to the US Centers for Disease Control and Prevention, with 21.1 percent of the population over the age of 18 being fully vaccinated.

On Thursday, the Biden administration announced formation of a group collectively called the COVID-19 Community Corps that will be part of an advertising campaign aimed at encouraging Americans to be inoculated against the coronavirus in communities where vaccine hesitancy remains high.

A recent survey by the Kaiser Family Foundation found that the number of Americans, particularly black adults, who want to get vaccinated is continuing to increase, but it also found that vaccine skepticism remains persistent, particularly among Republicans and white evangelical Christians.

The campaign, to air this month on network and cable television and online, comes as US health officials warn against a possible fourth surge of the virus.

The administration is working with 275 organizations in the campaign to get more Americans vaccinated, including NASCAR, the Catholic Health Association of the United States and the North American Meat Institute. Administration officials said the participating organizations are able to reach millions of Americans who trust them.