Most people understand that for every virus or bacteria, their can be multiple strains of the same organism that cause disease.
For example, there is flu A and B, swine flu, bird flu, and even dog flu.
In the case of flu, those different strains are a problem, because having immunity to one, doesn’t mean that you will have immunity to others. In fact, usually you won’t, whether it is natural immunity from a previous infection or immunity from a vaccine.
Pains with Strains
Do we have the same issues with other diseases?
We certainly have situations in which vaccines don’t cover all disease strains, including:
- Gardasil – now covers nine strains of HPV that cause 90% of cervical cancers
- Hib – only covers Haemophilus influenzae type b, which causes invasive disease, like meningitis, pneumonia, and sepsis, but not other Haemophilus influenzae strains that can cause ear infections
- Polio – originally protected against three serotypes of polio, but monovalent (one strain) and bivalent (two strains) oral poliovirus vaccines have also been available to respond to outbreaks and bOPV is the one used for routine immunization, except in industrialized, polio-free countries that use the IPV shot
- Prevnar – now covers 13 strains of Streptococcus pneumonia
- Rotavirus – protects against severe disease caused by rotavirus strains that aren’t even in the vaccine
Fortunately, even when a vaccine doesn’t cover all strains, it does cover those that most commonly cause disease.
What about measles?
There are at least 24 different genotypes of measles that come from 8 different clades (A-H), with even more wild type virus strains (based on those genotype).
These genotypes include A (all vaccine strains are genotype A), B2, B3, C1, C2, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, G2, G3, H1, and H2.
In general, genotypes are restricted to a specific part of the world, such as:
- African Region – B2, B3
- Eastern Mediterranean Region – B3, D4, D8
- European Region – D4, D5, D6
- Southeast Asian Region – D4, D5, D8, D9, G2, G3, H1
- Western Pacific Region – D5, D9, G3, H1
In countries that have eliminated measles, like the United States, the genotypes that are found will depend on from where the measles strain was imported.
Additionally, five genotypes, B1, D1, E, F, and G1 are now inactive.
Specific strains of measles viruses include the vaccine strains (Edmonston, Moraten, Zagreb, Schwarz, AIK‐C, CAM, Leningrad-16, and Shanghai-191, etc.) plus wild strains, like:
- MVi/NewYork.USA/94 – a wild strain of B3 genotype
- Johannesburg.SOA/88/1 – a wild strain of D2 genotype
- Manchester.UNK/30.94 – a wild strain of D8 genotype
- Hunan.CHN/93/7 – a wild strain of H1 genotype
Why so many vaccine strains?
It may come as a surprise to some people, but the whole world doesn’t use the same vaccines. For example, unlike the United States, Japan has used measles vaccines derived from AIK‐C, CAM, and Schwarz strains of the measles virus.
And just how many wild strains of measles are there? It’s hard to know, but consider that a study of 526 suspected measles cases from 15 outbreaks over 3 years in one state of India found at least 38 different strains.
Myths About Measles Strains
Do the measles vaccines cover all of the measles strains that cause outbreaks around the world?
Yes they do, despite the myths you may hear about mutated measles strains.
This came up a lot during the Disneyland measles outbreak, when folks first tried to place blame on a vaccine strain and then on the fact that the outbreak strain didn’t match the vaccine strain.
“…California patients were genotyped; all were measles genotype B3, which has caused a large outbreak recently in the Philippines…”
CDC Measles Outbreak — California, Dec 2014–Feb 2015
And it is coming again in the latest measles outbreak in Minnesota. Could that outbreak be caused by a vaccine strain? Anything is possible, but it’s not. A communication’s director for the Minnesota Department of Health has confirmed that “that the virus strain making people sick in this outbreak is the B3 wild-type virus.”
Of course, none of these outbreaks are started by a vaccine strain of measles shed from someone who was recently vaccinated. It also had nothing to do with the fact that the strains didn’t match – after all we aren’t talking about the flu.
These outbreaks are imported from other countries by folks who typically aren’t vaccinated or are incompletely vaccinated and mostly spread among other people who are unvaccinated.
So what’s the most important thing to understand when considering all of these vaccine strains and wild strains of measles? It is that “there is only 1 serotype for measles, and serum samples from vaccinees neutralize viruses from a wide range of genotypes…”
In other words, the measles vaccine works against all strains of measles in all genotypes of measles. That makes sense too, because the measles virus, unlike influenza, is monotypic.
There is only one main type of measles virus, despite the many small changes in the virus that can help us identify different strains and genotypes. And these changes don’t affect how antibodies protect us against the measles virus.
What To Know About Measles Strains
The best way to get protected against all measles strains is to get vaccinated with two doses of the MMR vaccine.
More About Measles Strains
- How I Accidentally Started an Anti-Vaxx Myth in the Name of Science
- Is the measles outbreak that occurred in Disney Land of a different strain than what’s in the vaccine?
- Genotypes, Serotypes and the MMR: Cognitive Dissonance in Action
- Study – Genetic Characterization of Measles Vaccine Strains
- Report – Global Distribution of Measles Genotypes and Measles Molecular Epidemiology
- Measles Surveillance Data
- Study – Identification of different lineages of measles virus strains circulating in Uttar Pradesh, North India
- Review – Elimination of endemic measles, rubella, and congenital rubella syndrome from the Western hemisphere: the US experience.
Updated May 23, 2017