LONDON - A new study from the United Kingdom revealed one shot of the Pfizer/BioNTech vaccine boosted protection against COVID-19 variants - but only for those who had been previously infected with the virus.Researches from Imperial College London, Queen Mary University of London and University College London published their study on Friday.Scientists looked at the immune responses of health care workers from Barts and Royal Free hospitals after they’d received one shot of the Pfizer/BioNTech vaccine, which requires two doses.Blood samples were analyzed to measure the immunity against the COVID-19 variants. RELATED: UK variant a 'brand new ballgame,' infecting children in US 'very readily,' epidemiologist warnsThe data revealed that those.