Covid-19: Some Johnson & Johnson Vaccine Doses on Hold in U.S. After Factory Mix-Up Last Updated April 1, 2021, 5:05 a.m. ETApril 1, 2021, 5:05 a.m. ET France will enter its third national lockdown. The Pfizer-BioNTech vaccine is highly effective in adolescents, a study suggests. This briefing has ended. An Emergent BioSolutions lab in Baltimore.Credit...Michael Robinson Chavez/The Washington Post, via Getty Images Workers at a plant in Baltimore manufacturing two coronavirus vaccines accidentally conflated the ingredients several weeks ago, contaminating up to 15 million doses of Johnson & Johnson’s vaccine and forcing regulators to delay authorization of the plant’s production lines.