Table 1.

Basic reproductive number and antigenic diversity of certain viruses

Virus	Reproductive No.	Antigenic diversity
Measles	12-18[4]	Stable, single serotype, long-lasting immunity
Mumps	5-7[4]	Stable, single serotype, long-lasting immunity
Rubella	5-7[4]	Stable, single serotype, long-lasting immunity
Poliovirus	5-7[4]	Stable, 3 serotypes, long-lasting immunity
Respiratory syncytial virus	1-2[16]	Two major antigenic groups, multiple antigenic variants within the groups, re-infection can occur[17,18]
Influenza	1-2[2,3]	Antigenic drift, numerous antigenic variants, re-infection is common