Moraten strain

Moraten strain. The Moraten strain is a live attenuated virus used as the standard component in measles vaccines throughout much of the world, particularly in the United States. Derived from the original Edmonston strain isolated by John F. Enders, it was further attenuated by Maurice Hilleman at Merck & Co. to reduce adverse reactions. Its introduction represented a pivotal advancement in the global effort to control and eliminate the highly contagious measles disease.

History and development

The lineage of this viral isolate began with the seminal work of John F. Enders and his team, who first isolated the progenitor Edmonston strain in 1954 from a patient named David Edmonston. This breakthrough, for which Enders shared the Nobel Prize in Physiology or Medicine, enabled the first generation of measles vaccines. Seeking to improve upon the reactogenicity of the initial Enders vaccine, researcher Maurice Hilleman at the pharmaceutical company Merck & Co. undertook a further attenuation process. Through additional passages in chick embryo tissue culture, Hilleman developed a more attenuated derivative which he named "Moraten," a portmanteau meaning "more attenuated Enders." This strain was subsequently licensed in the United States and became a cornerstone of public health strategy, supported by organizations like the World Health Organization and the Centers for Disease Control and Prevention.

Characteristics and attenuation

This isolate exhibits specific genetic and phenotypic markers resulting from its serial passage history. The attenuation process involved culturing the virus in cells from chick embryos, which selected for variants adapted to avian cells and less suited to human physiology. Compared to its parental Edmonston strain, it demonstrates a reduced replication capacity in human tissues, leading to a lower incidence of fever and rash in vaccine recipients. The strain is genetically stable and does not revert to a wild-type pathogenic form, a critical safety feature for a live attenuated vaccine. Its antigenic profile remains effectively identical to circulating wild-type measles virus, ensuring that the immune response it elicits provides robust protection against natural infection.

Vaccine usage and efficacy

The strain is exclusively used in the measles component of the combined MMR vaccine, which also immunizes against mumps and rubella, and the MMRV vaccine, which adds protection against varicella. Administered via subcutaneous injection, a single dose typically induces protective antibodies in over 95% of susceptible individuals aged 12 months or older. The implementation of a two-dose schedule, as recommended by the Advisory Committee on Immunization Practices, pushes population efficacy toward 99%, crucial for establishing herd immunity. Vaccine efficacy has been instrumental in the dramatic decline of measles cases and complications such as subacute sclerosing panencephalitis in countries with high vaccination coverage. Its use is a central pillar of the World Health Organization's Measles & Rubella Initiative.

Global distribution and impact

While the strain is the predominant measles vaccine used in the Americas and many nations, other attenuated strains like Schwarz strain and AIK-C strain are used in different regions. Its widespread adoption, particularly through the Expanded Programme on Immunization, has had a profound global impact. The Pan American Health Organization declared the elimination of endemic measles in the Americas in 2016, a milestone achieved largely through vaccination with this strain. Despite this success, ongoing outbreaks in areas with low coverage, such as certain communities in Europe and the Philippines, underscore the necessity of maintaining high vaccination rates. Global eradication remains a goal of major health bodies, though challenges persist in regions like the Democratic Republic of the Congo and Yemen.

Related strains and variants

The Moraten strain belongs to a family of vaccines descended from the original Edmonston strain. Its closest relative is the Edmonston-Zagreb strain, which uses a different passage history and is employed in some high-titer vaccine formulations. The Schwarz strain, developed concurrently by another researcher, is another further-attenuated Edmonston derivative used extensively by UNICEF and the GAVI Alliance. Other notable variants include the CAM-70 strain and the TD97 strain, developed in Japan and China, respectively. The continued genetic surveillance of wild-type measles viruses by networks like the Measles Nucleotide Surveillance helps monitor the match between vaccine strains and circulating genotypes, ensuring ongoing vaccine effectiveness.

Category:Vaccines Category:Virology Category:Public health