Rubella is a human disease and animal reservoir has not yet identified. It is an acute, viral disease characterized by mild febrile rash illness. Rubella is a self-limited illness usually occurs during childhood. The rubella virus is transmitted through person-to-person contact and droplet nuclei from respiratory secretions. Its incubation period ranges from 12 to 23 days. Although it is a moderately contagious disease, it remains the most contagious when rashes appear. However the virus may be shed from 7 days before to 5-7 days or more after the onset of rashes. The disease usually occurs in a seasonal pattern, with epidemics every 5-9 years. However, the extent and periodicity of its epidemics is highly variable in both industrialized and developing countries.
Congenital rubella syndrome- CRS, is a serious consequence of rubella infection in pregnancy. The outcome of primary rubella infection during pregnancy includes spontaneous abortion, stillbirth, foetal death, infant born with congenital rubella syndrome. The most common defects of CRS are hearing impairment- unilateral or bilateral sensorineural, eye defects- cataracts, congenital glaucoma, or pigmentary retinopathy, and cardiac defects- patent ductus arteriosus, or peripheral pulmonic stenosis. Other clinical manifestations may include microcephaly, meningo-encephalitis, hepato-splenomegaly, purpura, low birth weight, developmental delay and radiolucent bone disease. The risk of congenital infection is related to the gestational age at the time of maternal infection. The period of highest risk of CRS is up to 90 percent of cases from just before conception and during the first 8-10 weeks of gestation.
Manifestations of CRS may be delayed from 2 to 4 years. Diabetes mellitus appearing in later childhood occurs frequently in children with CRS. In addition, progressive encephalopathy resembling subacutesclerosing panencephalitis has been observed in some older children with CRS. Rubella and CRS were documented as significant public health problems in Nepal.
*General Secretary, Nepal Public Health Association, Kathmandu
Public Health Aspects
Rubella has a worldwide distribution. It usually occurs in temperate zones during the late winter and spring, with epidemics every 5-9 years. However, the extent and periodicity of rubella epidemics is highly variable in both developed and developing countries. The reasons for this are not known.
Before the introduction of large-scale rubella vaccination, the average age at which children were infected varied between 6-12 years in industrialized areas and 2-8 years in urban areas of developing countries. The highest risk of CRS is found in countries with high susceptibility rates among women of childbearing age. Although low susceptibility rates have been reported in studies of selected populations within some countries, these may reflect local variations, and extrapolating from such studies could mask a significant national benefit from the introduction of rubella vaccination.
Rubella/CRS Situation in Nepal
After the catch-up and follow up measles campaigns in 2005 and 2008, the measles cases were dramatically reduced and unmasked the ongoing transmission of rubella cases. There were 11 confirmed rubella outbreaks reported in 2007, 29 in 2008, 59 in 2009 and 19 in 2010. A total of 15,535 febrile rash illness cases reported during 2004 to 2009, of which 10,116 were from outbreak investigations and 5,419 were from sentinel surveillance reporting. Of 15,535 cases 3,710 (24%) of reported febrile cases were confirmed rubella (1,187 lab-confirmed and 2,523 (Eilinked rubella).
Rubella cases show seasonal distribution peaking in late winter and early spring. A sero-prevalence study among women in childbearing age (15-39 years) conducted in 2008 showed an estimated 6,091 pregnant women infected with rubella and 1,426 estimated infants born with CRS with rate of 192/100,000 live births. A cross-sectional study conducted in August 2009 in students attending a School for the Deaf, documented the presence of CRS.
Rubella Vaccines and Immunogenicity
Most rubella vaccines are based on the live, attenuated RA 27/3 strain. Rubella containing vaccines (RCVs) are available either as monovalent formulations or, more commonly, in combinations with vaccines against measles (MR), measles and mumps (MMR), or measles, mumps and varicella (MMRV). The immune response to rubella antigens is not affected by the other vaccine components.
Rubella containing vaccines (RCVs) are administered subcutaneously usually at the age of 12-15 months, but may be administered to children aged 9-11 months and to older children, adolescents, and adults. Although one dose of rubella vaccine probably induces life-long protection, in most countries using the MR or MMR vaccines a second dose is offered at 15-18 months or 4-6 years, as indicated for protection against measles and mumps.
In clinical trials, 95-100% of susceptible persons aged ≥12 months develop rubella antibodies after a single dose of the vaccine. In outbreak situations the effectiveness of different rubella vaccines has been estimated at 90-100%. RA 27/3-containing vaccines have eliminated rubella and CRS from the western hemisphere and in European countries with high vaccination coverage.
Natural rubella infection normally confers lifelong immunity. There have been rare cases of serologically documented reinfections either after earlier natural infection or after vaccination. Reinfection in pregnancy resulting in CRS has occasionally been reported in women with natural or vaccine-induced immunity, but the risk to the fetus is low. Antibodies are first detectable about 14-18 days after acquired rubella infection at about the time the maculopapular rash appears.
Adverse reactions following vaccination with RA27/3-containing rubella vaccine are mild, particularly in children. However, in susceptible adult women, transient arthralgias and arthritis are relatively common. Rubella vaccination of pregnant women is not recommended, and pregnancies should be avoided for 1 month following rubella vaccination. Rubella vaccination is contraindicated for people with a history of an anaphylactic reaction to components of the vaccine and for persons suffering from severe immunodeficiency.
Vaccination Strategies
The primary purpose of rubella vaccination is to prevent the occurrence of congenital rubella infection, which is an important cause of deafness, blindness and mental retardation. There are two general approaches to the use of rubella vaccine: (i) the first focuses exclusively on reducing CRS by immunizing adolescent girls and/or women of childbearing age; (ii) the second approach aims at interrupting viral transmission and thereby eliminating rubella as well as CRS.
For CRS reduction alone, adolescent and adult females should be vaccinated through either routine services or supplementary immunization activities. This option will provide direct protection to women of childbearing age; however, the impact of this strategy is limited by the coverage achieved and the age groups targeted. In the absence of a program that ensures vaccination of infants and young children, rubella will continue to circulate, resulting in ongoing exposure of pregnant women and the associated risk of CRS.
For the elimination of rubella and CRS, the preferred approach is to begin with MR vaccine or MMR vaccine in a campaign targeting a wide range of ages, immediately followed by the introduction of MR or MMR vaccine into the routine immunization program. All subsequent follow-up campaigns should use MR vaccine or MMR vaccine. In addition, countries should make efforts to reach women of childbearing age by immunizing adolescent girls or women of childbearing age, or both, either through routine services or mass campaigns. Measles-vaccine delivery strategies provide an opportunity for synergy and a platform for advancing rubella and CRS elimination. All countries that are providing two doses of measles vaccine using routine immunization or SIAs, or both, should consider including RCVs in their immunization program.
Depending on the burden of disease and the available resources, countries may choose to accelerate their progress towards elimination by conducting campaigns targeting a wide range of ages of both adult males and females. The precise target population addressed will depend on the country's susceptibility profile, cultural acceptability and operational feasibility.
Sustained low coverage of rubella immunization in infants and young children can result in increased susceptibility among women that may increase the risk of CRS above levels during the pre-vaccine era. Therefore, countries should achieve and maintain immunization coverage of ≥80% with at least one dose of an RCV delivered through routine services or regular SIAs. The need to document the impact of rubella vaccination requires laboratory-supported surveillance for rubella and CRS, and molecular epidemiology. Immunization coverage should be monitored by age and locality and supplemented by seroprevalence surveys where necessary to determine age-specific susceptibility to rubella and direct vaccination activities. Antenatal serological screening is a practical tool in this context.
Synergy with Measles Vaccination Programs
Measles vaccine delivery strategies provide an opportunity for synergy and a platform for advancing rubella and CRS elimination. All countries that are providing two doses of measles vaccine using routine immunization or supplementary immunization activities should consider including RCVs in their immunization program. Cost-benefit studies of rubella vaccination have shown that benefits outweigh costs and that rubella vaccination is economically justified, particularly when combined with measles vaccine.
Surveillance
Susceptibility or immunity to rubella can be ascertained only by serological tests. Sero-prevalence studies, using a representative sampling approach and reliable laboratory testing procedures, may be useful in monitoring susceptibility and determining the age groups for vaccination during SIAs. Antenatal serological screening is a practical tool for surveillance in this context. However, serological testing may be expensive and should be used as a supplementary tool in addition to monitoring immunization coverage and conducting surveillance for rubella and CRS. However, serological screening for susceptibility is not recommended before rubella vaccination. Field and laboratory surveillance for rubella should be integrated with measles surveillance in a single system. Also, surveillance for CRS should be initiated. The need to document the impact of rubella vaccination will require laboratory-supported surveillance for rubella, CRS surveillance, and molecular epidemiology, as outlined in WHO surveillance guidelines.
