People who got Johnson & Johnson Inc’s Covid-19 vaccine as a first shot had a stronger immune response when boosted with vaccines from Pfizer Inc/BioNTech SE or Moderna Inc, a study run by the National Institutes of Health showed on Wednesday.

The study, which included more than 450 adults who received initial shots from Pfizer, Moderna, or Johnson & Johnson, showed that "mixing and matching" booster shots of different types is safe in adults. Moderna's and Pfizer's vaccines are based on messenger RNA while J&J's uses...