Measles virus is an enveloped, ribonucleic acid virus of the genus Morbillivirus. Although at least 20 different genotypes have been isolated in various parts of the world, there is only one serotype. Measles is highly contagious, and an infected person will often transmit the virus to over 90% of unprotected close contacts.
Following inhalation of virus-containing droplets, measles virus replicates in the cells of the nose and throat, and 5-7 days after exposure infection is spread through the blood to the skin, the eye, and the respiratory tract. Patients develop high fever, cold-like symptoms, and conjunctivitis. A typical rash appears after another 3-4 days, spreading from the face and neck to the trunk and extremities. While most persons recover from measles without lasting effects, severe forms of the disease with bleeding from skin and mucosa may occur. Among children less than 5 years of age measles complications frequently include otitis media and pneumonia. Persons with malnutrition, especially vitamin A deficiency, or with severe immunological disorders such as advanced HIV infection are at increased risk of developing severe or even fatal measles.
The envelope of measles virus contains haemagglutinin that is responsible for the binding of the virus to the host cell surface and a fusion protein that facilitates viral uptake into the cell. Antibodies to haemagglutinin correlate with protection against the disease. A number of live, attenuated measles vaccines are available, either as monovalent vaccine or in combination with either rubella vaccine (MR) or mumps and rubella vaccines (MMR). Many of the attenuated strains in use are derived from the Edmonston strain isolated in 1954, including the Schwartz, the Edmonston-Zagreb, and the Moraten strains.
Other strains which are not derived from Edmonston strain include the CAM-70, TD 97, Leningrad-16, and Shanghai 191 (Ji-191) strains. Typically, the attenuated production virus is replicated in primary chick embryo or cell cultures, the virus harvested, clarified, and (alone, or with other antigens) lyophilized. The vaccine is reconstituted and generally injected subcutaneously, although intramuscular administration has also been shown to be effective. Measles vaccines have had a dramatic impact on measles morbidity and mortality, and programs for regional elimination of measles through high vaccine coverage of all children continue to reduce the number of cases.
Measles Vaccine Standardization
WHO first published the requirements for the production and quality control of inactivated and live measles vaccines in 1966. This document was revised in 1988 following the discontinuation of use of the inactivated vaccine and the increased use of eggs from closed colonies as well as cell cultures. As measles vaccines are routinely used in multi-antigen combinations with mumps and rubella vaccines, WHO updated the guidance for the three vaccines in 1992 into a single document which contains the requirements for the three monovalent vaccines and MMR.
Requirements for measles, mumps and rubella vaccines and combined vaccine (live), Technical Report Series No. 840, 1994, Annex 3
A WHO reference material for live attenuated measles vaccine is available to qualified applicants.
IABS Scientific Workshop on Neurovirulence Tests for Live Virus Vaccines, WHO, Geneva, Switzerland, 31 January-1 February 2005,
Prequalified measles vaccines
Measles and measles-containing vaccines (MR and MMR) are prequalified for procurement by UN organizations: