Identification:
A highly communicable but mild febrile viral disease with a diffuse punctuate maculopapular rash similar to measles and scarlet fever. Children usually have no other symptoms. Adults may experience a 1 to 5 day prodrome of low grade fever, malaise, mild coryza and conjunctivitis. Lymphadenopathy of post auricle, occipital and posterior cervical nodes is the most characteristic clinical feature and precedes rash by 5 to 10 days. Half of cases have no rash.
Infectious Agent:
Rubella virus.
Reservoir:
Humans.
Geographical Distribution:
Rubella occurs worldwide and the risk of exposure outside of North America can be high. Few countries routinely use this vaccine. Immigrant women from these risk countries (majority of Asia, Africa, South America and Central America including Mexico) are particularly susceptible.
An MMR immunization program for all infants was introduced in Canada in April 1983. Outbreaks still occur in clustered unimmunized populations. Fewer than 100 cases or rubella have been reported in each of the past 3 years and only 1-2 cases of CRS.
Mode of Transmission:
Contact with nasopharyngeal secretions of infected persons. Spread by droplet infection and by direct contact. Infants with CRS may shed the virus for months in secretions and urine.
Incubation Period:
14 to 21 days, commonly 14 to 17 days.
Period of Communicability:
One week prior to onset of rash until at least four days after rash appears. Highly communicable.
Susceptibility:
General. Active immunity is acquired by natural infection or by vaccination following first birthday.
Prevention:
Immunization with live attenuated rubella virus vaccine available in monovalent vaccine or in combination with measles and mumps as MMR.
The vaccine stimulates the formation of antibody in over 97% of susceptibles. Titres are generally lower than those observed in response to natural infection.
Asymptomatic re-infection has been noted in vaccines and may account for the continued endemicity of the disease.
Immunization schedules vary by province and can be obtained from local Public Health Departments. One dose of vaccine is recommended routinely on or as soon as practical after the first birthday in the combined MMR vaccine.
In all provinces and territories, a second dose of vaccine is given as MMR at 18 months of age or at school entry and at least one month after the first dose. This second dose is not necessary for achieving elimination of CRS but is thought to benefit those who failed to respond to primary immunization (1 to 3%).
The vaccine should be given to all females of childbearing age unless they have proof of immunity either in the form of a record or lab evidence of detectable antibody. A clinical history without lab confirmation is not a reliable indicator. Prenatal testing in Ontario and Quebec indicates serosusceptibilty rates of 7 to 11 %. Every effort should be made to immunize foreign-born women of childbearing age from risk areas. Women should be advised to avoid pregnancy for one month following immunization.
Up to one third of CRS cases occur in second and subsequent pregnancies therefore it is essential that all women found to be susceptible be immunized in the immediate postpartum period or as soon as practical after birth.
Studies indicate the duration of cellular and humeral immunity exceeds 20 years and since any detectable level protects against viremic infection, booster dosed are not considered necessary but are not harmful.
Preparations:
Available in the combined form as MMR 11 from Merck or as Priorix from GSK.
The vaccine incorporates the live attenuated virus strain RA 27/3 prepared in human diploid cell culture.
Vaccine should be stored in the frig between 2 to 8 degrees Celsius.
Once reconstituted it should be administered promptly.
It may be given at the same time but at different sites as DPT- containing vaccines. It may also be given at the same time as other live virus vaccines or if possible, separated by a 4 week interval.
The dose is 0.5 ml given as a subcutaneous injection.
Rash and lymphadenopathy occur occasionally. Acute transient arthritis or arthralgia may occur 1 to 3 weeks later and may persist for 1 to 3 weeks. The frequency and severity of these reactions increases with age and are more common in post-pubertal women.
Avoid administration during pregnancy. Do not administer to those known to be hypersensitive to the vaccine components such as antibiotics (e.g. neomycin) used in the preparation
Convincing evidence supports the safety of routine administration to all those who have allergy to eggs but at a facility with appropriate supportive treatment.
Breastfeeding is not a contraindication to immunization.
The vaccine should not be administered to those with impaired immune systems except under special circumstances. It may be given to HIV- infected people who are not severely immunosupressed in consultation with a specialist.
Vaccine must not be administered less than 2 weeks before an immune globulin injection and when this has been given then immunization should be delayed for 5 months if given as MMR and 3 months as monovalent serum.
Anti-Rho (D) may interfere with response so it should be given simultaneously and testing done 3 months later for immunity or wait for 3 months and then do titres.