ZURICH, Dec 27 (Reuters) - Swiss drugs regulator Swissmedic said on Monday it approved booster doses for Johnson & Johnson"s (JNJ.N) COVID-19 vaccine in people 18 years and older who have received a first vaccination. The second dose of the vaccine can be administered, at the earliest, two months after the first dose, Swissmedic said in a statement. It said mixed vaccinations with the J&J shot being administered six months after the second dose of Pfizer/BioNTech"s (PFE.N), (22UAy.DE) or Moderna"s (MRNA.O) mRNA vaccines were also authorised.