“In recent years, 13 Victorians have been hospitalized with measles despite having one or two vaccinations that should have made them immune. Why? Well, experts believe that because measles is so rare in Australia, we pretty much never come into contact with it, so our immune systems are starting to let their guards down and wane a little bit.”
Nathan Templeton on Measles Immunity Concerns
What is he talking about?
It’s the idea of exogenous boosting from being around natural infections. In other words, after you become immune from being vaccinated, you could get a boost in your immune protection if you are around someone with the disease.
“The exogenous boosting (EB) hypothesis posits that cell-mediated immunity is boosted for individuals reexposed to varicella-zoster virus (VZV).”
Talbird et al on Understanding the role of exogenous boosting in modeling varicella vaccination.
While this is thought to happen with chickenpox, we aren’t sure if it happens with measles.
It might, but the “problem” is that it is known that folks can have an amnestic response, so can be immune even though they have low antibody levels.
Mostly though, it is important to keep in mind that most of the people who get measles are unvaccinated, often intentionally unvaccinated.
“The key to measles elimination is increasing vaccination coverage and monitoring of measles antibody status for all ages, as well as enhancing surveillance of both domestic and overseas incidences.”
Inaida et al on Measles elimination and immunisation: national surveillance trends in Japan, 2008-2015.
So how many vaccinated Australians are getting measles?
“In Australia, the majority of measles cases are due to unvaccinated individuals becoming infected while travelling to countries in which measles is either common or there are outbreaks occurring. As measles is highly contagious, these people can then spread the disease to others, causing outbreaks, often before they are aware that they have the virus.”
Australia’s Measles Outbreaks 2019
And just as in the United States and most other countries, most of their outbreaks are started by folks who are unvaccinated.
Traditionally, the time when measles case counts are the highest occurs:
during the late winter and early spring (temperate climates, like the United States)
after the rainy season (tropical climates)
when kids are in school
So just like flu season, it’s always measles season somewhere…
And in areas of the world where measles is still highly endemic, you can expect cycles of larger measles epidemics every 1 to 4 years.
Can you guess why?
“As higher uniform population immunity is achieved the scale of epidemics, both their duration and absolute number of cases, progressively decreases. Epidemic frequency simultaneously decreases with increasing time intervals between epidemics. Another uniform feature as elimination is approached is the loss of epidemic seasonality.”
Durrheim et al on Measles – The epidemiology of elimination
I’ll give you a hint – there is nothing different about the measles virus during those years.
Eventually though, as the number of people susceptible to measles builds up, there is the opportunity for bigger outbreaks. Of course, that doesn’t happen if most people are vaccinated and protected.
“Source countries included Philippines (14 cases), Ukraine (8), Israel (5), Thailand (3), Vietnam (2), Germany (2), and one importation each from Algeria, France, India, Lithuania, Russia, and the United Kingdom.”
Increase in Measles Cases — United States, January 1–April 26, 2019
In the early part of 2019, we saw a lot of cases because unvaccinated travelers were returning from Philippines, Ukraine, and Israel, countries in peak measles season.
As cases in those countries hopefully slow down over the summer, unfortunately, we might see a rise in other parts of the world.
Of course, there is an easy way to end our measles seasons once and for all.
Get vaccinated and protected, especially before traveling out of the country.
There are also many countries with rather small numbers of cases that are seeing measles deaths.
In Samoa, a country that stopped vaccinating last year after two infants tragically died when they got a powerful anesthetic instead of the diluent for the MMR vaccine, over 80 people have died already.
And don’t forget that the last death in France, in April 2019, occurred after only 852 cases were reported.
In Romania, the first death of 2019, in January, came after just 133 cases.
And since the outbreaks in Europe started in 2016, there have been deaths in:
Bulgaria – only 416 cases
Portugal – only 202 cases
Spain – only 457 cases
Switzerland – two deaths and only 197 cases!
Hungary – only 24 cases!
Of course, there are more deaths in countries that are seeing more cases.
Measles deaths are on the rise too. While the risk of complications of measles can be reduced with vitamin A treatment, that doesn’t eliminate them. And the benefit is mostly in those who are already vitamin A deficient. Vitamin A has a much more modest effect in developed countries, where measles deaths still occur.
What to reduce your child’s risk of dying from measles?
Do you remember when measles was eliminated in the United States?
You probably should.
It wasn’t that long ago…
When Measles Was Eliminated in the United States
After several years of declining numbers of measles outbreaks in the United States, the endemic spread of measles was declared eliminated in March 2000.
“The data indicated that, during 1997–1999, measles incidence has remained low (<0.5 cases per 1,000,000 population) and that most states and 99% of counties reported no measles cases. In addition, measles surveillance was sensitive enough to consistently detect imported cases, isolated cases, and small outbreaks. Evidence of high population immunity included coverage of >90% with the first dose of measles vaccine in children aged 19–35 months since 1996 and 98% coverage among children entering school. In 48 states and the District of Columbia, a second dose of measles vaccine is required for school entry. A national serosurvey indicated that 93% of persons aged >6 years have antibody to measles.”
So, measles wasn’t gone yet. It was just that most cases were imported from outside the country. Only imported strains of the measles virus were causing outbreaks.
“The end of endemic measles transmission in the United States has both domestic and international importance. Domestically, the absence of endemic exposure to measles means few persons in the United States will be infected and risk complications of measles. This decreased risk of exposure provides protection to groups not protected directly by vaccination: children too young for routine vaccination; the few persons who, although vaccinated, are not protected, primarily from failure to mount an adequate response to vaccine; persons for whom vaccine is contraindicated (e.g., those with immunodeficiency); and persons who choose not to be vaccinated.”
Wharton on Measles Elimination in the United States
Unfortunately, the “choose not to be vaccinated” group might be endagering our claim to have eliminated measles.
“Endemic measles transmission is the existence of any continuous indigenous chain of transmission of measles virus that persists for >1 year in any defined geographic area (e.g., the United States).”
Orenstein on Defining and Assessing Measles Elimination Goals
Still, when you look at the numbers, technically, measles isn’t yet spreading endemically in the United States.
We are getting close though.
The outbreaks in Rockland County and Brooklyn started in September and October 2018. If they aren’t stopped soon, will it be easier to make a case that measles is no longer eliminated in the United States?
“Outbreaks in New York City and Rockland County, New York have continued for nearly 8 months. If these outbreaks continue through summer and fall, the United States may lose its measles elimination status.”
U.S. measles cases in first five months of 2019 surpass total cases per year for past 25 years
It sounds like it.
One thing to consider though, after an unvaccinated visitor introduced measles to Brooklyn from Israel back in October, measles has been reintroduced into the community at least seven other times! This includes travelers from Israel, UK, and Ukraine.
So the outbreak isn’t necessarily a “continuous indigenous chain of transmission of measles virus.”
It is multiple chains in the same community.
“There have been additional cases of measles from international travelers to Rockland, exposing more people to measles.”
2018 – 2019 Measles Outbreak in Rockland County
The same thing has happened in Rockland County after the initial importation from Israel in September.
Measles Elimination Criteria
Does that matter?
It likely should, but let’s also look at how we do with other criteria that are often used to assess the absence of the endemic spread of measles:
Few measles cases/low measles incidence – we will have the most cases in 2019 since 1992, but most cases are clustered in just a few big outbreaks
The duration of outbreaks is short – outbreaks are getting longer and harder to contain, but part of the problem is the global rise in measles and the reintroduction of measles into existing outbreaks
Most cases are associated with international importation – still very true
No endemic measles virus strain – outbreaks this year have been associated with strains that are commonly seen in Ukraine, the Philippines, and a few other areas