1.8 Epidemiologic features of rubella and CRS

Mick Mulders

Rubella has a worldwide distribution except in countries where the disease has been eliminated. It usually occurs in a seasonal pattern (i.e. in temperate zones during the late winter and spring), with epidemics every five to nine years. However, the extent and periodicity of rubella epidemics is highly variable in both developed and developing countries.

Rubella is spread through contact with respiratory secretions of an infected person. This may result from airborne droplet spread, direct contact with an infected person or indirect contact with freshly infected articles. Rubella is moderately contagious, primarily just before and just after the appearance of the rash, but transmission of virus can occur from 1 week before the onset of the rash and up to 1 week after the appearance of rash. Infants with CRS shed large quantities of rubella virus in their pharyngeal secretions and in urine, and can serve as a source of transmission. In closed institutions, such as in military barracks and child day-care centres, all exposed and susceptible individuals may become infected. The Ro for rubella is 6-7, less than half that for measles. To interrupt transmission of rubella, a herd immunity threshold of approximately 83-85% is required [18].

An estimate of worldwide CRS incidence in 2010 was 105,000 cases (95% CI: 54,000-158,000) [27]. The majority of these cases occur in developing countries that have not yet introduced rubella vaccine. Many countries have not yet included CRS in their communicable disease surveillance systems and not all countries with well-established CRS surveillance have provided complete data to regional offices or to WHO/UNICEF. Therefore, until more countries establish an effective CRS surveillance and reporting system, a more precise estimate of the burden of rubella cannot be provided.

The existing, internationally-licensed rubella vaccines, single or in combination with vaccines against measles (and mumps) have proved to be highly efficacious in the prevention of rubella infection and CRS in different parts of the world. Seroconversion following a single dose is ≥95%. Through immunization programmes, endemic transmission of rubella virus has been successfully eliminated in the western hemisphere and several European countries. Rubella-containing vaccine is usually administered in a combination vaccine with measles-containing vaccine, following the schedule recommended for measles [26,28].