Hospitals around the nation earlier this year began imposing COVID-19 vaccine mandates, but employees were told they’d meet the requirements if they received the single-shot Johnson & Johnson (J&J) vaccine. That’s changed at a New Jersey hospital, where employees now must get a booster if they received the single-shot jab. University Hospital in Newark on Wednesday announced employees have until Dec. 24—Christmas Eve—to get an additional vaccine dose. Per federal guidance, the workers can choose from any of the three COVID-19 vaccines authorized in the United States, including J&J. Drug regulators last week said Americans could mix and match booster shots. Workers who got the Moderna or Pfizer vaccine do not need to get an additional shot at this time, though hospital leadership did not rule out a future widening of the booster mandate. “Data and analysis indicate that a single dose of the Johnson & Johnson vaccine may no longer …