I’m an infectious disease researcher and the mother of two children, so I’m usually the first person friends and family turn to whenever a disease is in the news. Since the Disneyland measles outbreak, I’ve responded to a lot of myths and misinformation from concerned parents.
As a mother I understand what it’s like to to want to arm yourself with as much information as possible to protect your children. As an infectious disease researcher it’s frustrating to see people without knowledge of virology nor immunology misconstrue science, or simply ignore it, and spread dangerous misinformation.
A new anti-vaxx myth has surfaced which seems to have been developed as a result of my recent post “Disneyland Measles Outbreak is Due to Measles”, which discussed the measles genotype responsible for this outbreak. The post was a response to another circulating myth that the measles strain is unknown and could be the strain found in the vaccine. It seems my post was then misconstrued and has become the basis of yet another anti-vax myth.
The new myth goes like this: since the measles strain in the MMR vaccine is genotype A, the vaccine doesn’t protect against the strain of the measles responsible for the Disneyland outbreak, which is genotype B3. This is not true and I want you to know how and why it’s not true. The MMR vaccine does provide cross-protective coverage for wild-type measles strains such as B3.
Before I get into the how and why, though, I want to define some terms:
- RNA: Ribonucleic Acid are strings of nucleic acid, similar to DNA, that acts as a messenger of genetic information.
- Genotype: The small differences within a specific region in the RNA or DNA of a species of microorganism.
- Antigen: A protein on the surface of a virus or bacteria that provokes an immune system response.
- Serotype: The same species of microorganism such as virus or bacteria that can be further divided into sub-groups based upon their surface antigens.
- Epitope: The very specific part of the antigen which antibodies attach to.
- Strain: A generic term to refer to subgroups of a virus or bacteria that include the above variables.
When a physician suspects a patient has the measles they take a sample from the patient through a throat or nasal swab and send it to be genetically sequenced. Epidemiologists use two genes within the measles virus to determine the virus’ genotype, specifically they look at regions of nucleotide sequences in the RNA called hemagglutinin (H) and nucleoprotein (N). This is where we get the labels genotype A and genotype B.
The measles virus has only one serotype which causes only one illness, unlike Human Papillomavirus which has dozens of serotypes and can cause different diseases. This is why we see multiple serotypes included in the HPV vaccine and only one strain in each of the available measles vaccines which are all genotype A. Additionally, Unlike other viruses, such as the flu, the genotypes within strains of the measles virus only vary ~12% at the nucleotide level.
For these reasons, studies including millions of individuals have shown that the genotype A strain in the measles vaccines available today produce the antibodies necessary to provide immunity to all strains of the measles.
Measles viruses recovered through testing are constantly monitored, analyzed and characterized to identify areas of the genome which may antigenically-drift. The measles viruses currently circulating have also been tested against vaccine-derived antibodies to ensure vaccines will cross-protect against the numerous genotypes that have been detected in different parts of the world.
There are tests such as virus neutralisation assays that combine different measles viruses with serum samples (the antibody-rich fraction of blood) of people who have either been vaccinated or previously infected with wild-type measles to determine if antibody binding occurs to different measles genotypes. A fluorescent tag is added in order to visualize a reaction and then the antibody-antigen complex is measured. Results of numerous studies demonstrate that vaccine-derived antibodies protect against many different measles genotypes:
One of the tools public health agencies such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) use to monitor and test the efficacy of the measles vaccines are antibodies called monoclonal antibodies (MAbs) and have found that between the vaccine strain (genotype A) and wild type measles viruses (genotypes B-D) the measles vaccines currently available offer protection against these strains.
Specifically, the CDC and the WHO have found that the current measles vaccines offer protection against measles genotype, B3 the strain responsible for the Disneyland outbreak.
It is frustrating to know that a post I intended to inform and educate parents has been used to fuel a myth that may put their children at risk. If any further evidence was needed to support that the MMR vaccine is effective against the Disneyland measles outbreak, which has sickened 121 people to date (dozens more reported), only 7% of those infected had received two doses of the MMR vaccine. If the MMR and MMRV vaccines were ineffective against genotype B3 we would see many more people with both doses of the vaccine test positive for the measles.
Measles is one of the most infectious diseases we know of and this interactive infographic demonstrates how measles can spread in variable susceptible populations. If the vaccine did not proffer cross-protection, there would be tens of thousands of cases to date. Help me save lives and It is a public health imperative that parents have accurate information in order to feel confident that the available measles vaccine do work and have an excellent safety profile.
Science Mom. Disneyland Measles Outbreak is Due to The Measles
. JustTheVax.Blogspot.com. January 28, 2015. Retrieved February 16, 2015.
The RNA Society. What is RNA? Retrieved February 16, 2015.
Blamaire, J. Genotype and Phenotype Definitions. City University New York. 2000. Retrieved February 16, 2015.
National Institutes of Health. Antigen Definition. Medline Plus. August 11, 2013. Retrieved February 16, 2015.
Centers for Disease Control and Prevention. Serotypes and the Importance of Serotyping Salmonella. April 8, 2014. Retrieved February 16, 2015.
Medicinenet.com. Epitope Definition. June 16, 2012. Retrieved February 16, 2015.
Wikipedia. Strain (biology). Retrieved February 16, 2015.
Centers for Disease Control and Prevention. Specimens for Detection of Measles RNA by RT–PCR or Virus Isolation. November 3, 2014. Retrieved February 16, 2015.
Centers for Disease Control and Prevention. Genetic Analysis of Measles Viruses. November 3, 2014. Retrieved February 16, 2015.
“Wild-type measles viruses have been divided into distinct genetic groups, referred to as genotypes, based on the nucleotide sequences of their hemagglutinin (H) and nucleoprotein (N) genes, which are the most variable genes on the viral genome.
The 450 nucleotides encoding the carboxy-terminal 150 amino acids of the nucleoprotein has up to 12% nucleotide variation between genotypes. The 450 nucleotides that encode the carboxy-terminal region of the nucleoprotein (N–450) are required for determination of the genotype. The measles genotyping protocol is available from CDC.”
World Health Organization. Measles. March 11, 2013. Retrieved February 16, 2015.
“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.”
Growdon, W. B., & Del Carmen, M. (2008). Human Papillomavirus-Related Gynecologic Neoplasms: Screening and Prevention. Reviews in Obstetrics and Gynecology, 1(4), 154–161.
Centers for Disease Control and Prevention. Serologic Testing for Measles in Low Prevalence Setting. November 3, 2014. Retrieved February 16, 2015.
Tamin, A., Rota, P., Wang, Z. et al., Antigenic Analysis Of Current Wild Type And Vaccine Strains Of Measles Virus. Journal of Infectious Diseases. (1994) 170 (4): 795-801.doi: 10.1093/infdis/170.4.795
“The serum samples from recently vaccinated persons neutralized both the Moraten and Chicago-I viruses equally well (table 1): There was a <2-fold difference in neutralization titers. In contrast, serum samples from persons with a recent wild type infection were able to detect antigenic differences between the viruses. Sera in this set had neutralization titers against Chicago-l that were 4-8 times higher (average, 5.1) than the titers against the vaccine strain.”
Bankamp, B., Takeda, M., Zhang, Y. Genetic Characterization of Measles Vaccine Strains. Journal of Infectious Diseases. (2011) 204 (suppl 1):S533-S548.doi: 10.1093/infdis/jir097
“On the basis of the sequences of their N and H genes, MeVs can be assigned to 1 of 23 genotypes and 1 provisional genotype [11, 12]. All vaccine strains and their wild-type progenitors are assigned to genotype A. Experiments with monoclonal antibodies have defined antigenic differences between the H proteins of genotype A vaccines and the H proteins of wild-type viruses grouped in other genotypes [62, 188, 189]. However, there is only 1 serotype for measles, and serum samples from vaccines neutralize viruses from a wide range of genotypes, albeit with different neutralization titers [188, 190] More importantly, despite the presence of different endemic genotypes, vaccination programs with standard measles vaccines have been successful in every country where they were performed adequately [191–193]. Suboptimal seroconversion after vaccination is likely the result of inadequate coverage; improper administration, transport, or storage of vaccine; or age of the vaccine recipients [194–196].”
Centers for Disease Control and Prevention. Measles Outbreak — California, December 201–February 2015. Early Release. Morbidity and Mortality Weekly Report. February 13, 2015. Retrieved February 16, 2015.
Centers for Disease Control and Prevention & World Health Organization. History and Epidemiology of Global Smallpox Eradication. Slides 16-1. Retrieved February 16, 2015.
Harris, R., Popovich, N., Powell, K. Watch how the measles outbreak spreads when kids get vaccinated – and when they don’t. The Guardian. February 5, 2015. Retrieved February 16, 2015.