Increasing incidence of mumps in Scotland: options for reducing transmission

Abstract

Background: There has been a dramatic increase in mumps in Scotland since November 2003, with cases primarily in adolescents and young adults.

Objectives: This paper describes mumps epidemiology in Scotland, undertakes a risk assessment and considers option for reducing transmission.

Results: Mumps is primarily a risk for the 13-25 year age group, as they have neither been offered two routine doses of measles, mumps and rubella MMR vaccine, nor been exposed to wild virus. Transmission is facilitated by a high degree of social mixing, with enclosed settings (school, universities etc.) being higher risk. On the basis of susceptibility and risk of transmission, three categories of higher (17-20 years), intermediate (21-22; 15-16 years), and low (23-25; 13-14 years) risk were defined, all in higher risk enclosed settings. Herd immunity would be very difficult to achieve, as it would require unrealistically high MMR uptake (an additional 45-80% in 17-20 year olds). A risk management strategy of reducing transmission and decreasing the likelihood of outbreaks was therefore proposed. Action would be targeted at the higher risk group (17-20 years) in higher risk settings. Three options were considered: do nothing; opportunistic immunisation through GPs; a mass campaign. The 'do nothing' option was discounted. The preferred option was to alert GPs to the need to offer MMR vaccine to 17-20 year olds in higher risk settings. The rationale for this was that it had the lowest cost, avoided disruption to services, and primarily that it would reduce the probability of mumps transmission in higher risk settings.

Conclusions: The Chief Medical Officer issued a letter to all health professionals in Scotland encouraging them to offer MMR vaccine to 13-15 year olds, who had not previously received two doses, and particularly those aged 17-20 years in higher risk settings.