RT Journal Article SR Electronic(1) A1 Noah, N A1 Ramsay, M A1 Twisselmann, B YR 2001 T1 Imported cases of polio in Bulgaria – vaccination campaign postponed JF Weekly releases (1997–2007) VO 5 IS 21 SP 1747 OP DO https://doi.org/10.2807/esw.05.21.01747-en UL https://www.eurosurveillance.org/content/10.2807/esw.05.21.01747-en