Measles: highly contagious viral disease that can lead to severe complications and death. Mumps: contagious viral disease characterised by swelling of the salivary glands. Rubella: contagious viral infection and leading vaccine-preventable cause of birth defects. Varicella (chickenpox) is an acute, highly contagious disease caused by varicella-zoster virus (VZV). Following infection, the virus remains latent in neural ganglia and in about 10-20% of cases it is reactivated to cause herpes zoster, or shingles, generally in persons over 50 years of age or immunocompromised individuals. Almost one-third of the population will experience an outbreak of shingles during their lifetime.

Measles spreads easily when an infected person breathes, coughs or sneezes. Mumps is transmitted by aerosol and respiratory droplets. Rubella is transmitted by airborne droplets when infected people sneeze or cough. VZV transmission occurs via droplets, aerosols, or direct contact with respiratory secretions, and almost always produces clinical disease in susceptible individuals.

Measles: A prominent rash is the most visible symptom. Early symptoms usually last 4–7 days and include running nose, cough, red and watery eyes and small white spots inside the cheeks. Mumps: The most common clinical presentation of mumps is an acute and tender parotid swelling which develops 16–18 days after exposure in up to 70% of cases. Parotitis may be preceded by non-specific symptoms lasting 3–5 days including malaise, fever, headache, myalgia and arthralgia. Rubella: the infection usually causes a mild fever and rash in children and adults; during pregnancy, the infection can result in miscarriage, fetal death, stillbirth, or infants with congenital malformations, known as congenital rubella syndrome (CRS). Varicella is characterized by an itchy rash initially accompanied by fever and malaise. The rash gradually spreads to the trunk and extremities. The vesicles gradually dry out and crusts appear which then disappear over a period of one to two weeks. While mostly a mild disorder in childhood, varicella tends to be more severe in adults. It may be fatal, especially in neonates and in immunocompromised persons. The infection may occasionally be complicated by pneumonia or encephalitis (inflammation of the brain), at times with serious or fatal consequences.