Measles virus circulation in Argentina: 1991-1999.

Nucleoprotein (N) and Haemagglutinin (H) genes from measles viruses isolated from Argentina before and after the 1993 and 1998 massive vaccination campaigns were characterised to determine genetic variations that occurred from 1991 to 1999. Measles viruses from the 1991-94 period were clustered with the C1 genotype and those from 1997-99 with D6. Genetic variations within the 1997-99 outbreak were less than 1.2% and 0.79% for the N and H sequences respectively. The C1 genotype has not been detected since 1994 and the finding that a single D6 virus was found in November 1999 demonstrates that wild type viruses are still circulating among a partially covered population.