(Reuters) – The best defense against the evolution of COVID-19 and the emergence of variant strains is getting as many people vaccinated as quickly as possible, top U.S. infectious disease doctor Anthony Fauci said on a Monday media briefing.

Fauci said while it was reasonable to think about studying the efficacy of Pfizer’s and Moderna’s vaccine as a one-dose regimen in light of supply vaccine constraints, such a study would take months to complete, thus likely making its conclusions moot. Fauci continued to encourage people get two doses of the vaccine.

(Reporting by Carl O’Donnell, Editing by Franklin Paul)