Computer Simulation Just Predicted a Huge Measles Outbreak in Texas, With 4,000 Percent Increase Predicted in Some Communities

Texas could be hit by large measles outbreaks in which up to 400 people fall ill at a time, according to a forecast by researchers investigating low vaccine rates. Between 2003 and 2018, the number of children exempt from vaccines before attending school spiked from 23,000 to 64,000, according to existing research.

In the new paper published in the journal JAMA Network Open, the authors wrote: Decreases in vaccination rates in schools with undervaccinated populations in 2018 were associated with exponential increases in the potential size of outbreaks: a 5% decrease in vaccination rate was associated with a4 0% to 4000% increase in potential outbreak size, depending on the metropolitan area."

The team warned of "dramatic increases in the probability of large outbreaks" totaling more than 100 cases if trends continue.

In Austin and Dallas-Fort Worth, where vaccination rates are lower than 92 percent in a small number of schools, up to 400 cases could occur at a time, modelling predicted. An estimated average of 36 percent of those sickened in outbreaks involving at least 25 cases could happen in people other than unvaccinated children, the authors warned.

However, limiting the number of pupils who can be exempt from vaccination could tackle the problem, the researchers argued.

Vaccines partly work thanks to herd immunity. This is where a population is protected from an infectious disease because the vast majority of people have been vaccinated against it. This not only prevents the individual from falling ill, but it reduces their risk of passing the bug on to vulnerable people who can't receive vaccines because their immune system is too weak. Newborn babies and children with cancer fall into this category.

Thanks to the vaccine, measles was eliminated in the U.S. in 2000: defined as reduced to zero incidences for more than 12 months. But an outbreak has seen 1,203 cases confirmed by the Centers for Disease Control and Prevention this year.

In the past two decades, herd immunity has been jeopardized by a minority who decline to have vaccinations, the researchers explained. In Texas, parents can cite conscientious exemptions for both personal and religious reasons.

Some are put off by the false and widely debunked claims made by disgraced former doctor Andrew Wakefield. In 2010, he was struck from the medical register for publishing a 1998 study in The Lancet journal wrongly linking the MMR vaccine to autism. The work has since been shown to have no scientific basis. The former British doctor lives in Austin. The CDC reassures that the MMR shot provides "very safe and effective" protection against measles, mumps and rubella.

Caused by a virus, measles spreads when an infected person coughs or sneezes. This enables the bug to enter the body through the eyes, mouth or nose. The condition can trigger a rash that starts at the head before spreading to the rest of the body. As many as 90 percent of unvaccinated people who come into contact with an infected person will fall ill.

Measles can lead to serious complications, with one out of every 20 children getting pneumonia: the most common cause of death from measles in young children. Around one child out of every 1,000 will develop encephalitis (swelling of the brain) that can lead to convulsions and can leave the child deaf or with intellectual disability.

To calculate the risk of widespread measles outbreaks in school districts in Texas and beyond, the researchers looked at data on the size, location and vaccination rates of the state's school districts, as well as 2010 U.S. Census data. They crunched these numbers in a modelling tool to mock up a synthetic population of Texas and looked to see how an infected individual might affect different populations.

The authors suggested that areas with school outbreaks could adopt approaches used in New York State, such as isolating children or making vaccines mandatory.

As with any study, the findings were partly limited. In this instance, the authors acknowledged they were unable to access vaccination rates of specific schools.

David Sinclair, a postdoctoral researcher in Pitt's Public Health Dynamics Laboratory and lead author of the study, told Newsweek: "I was surprised at how large measles outbreaks could be in Texas at current vaccination rates, according to our forecasts. The clustering of unvaccinated children in certain schools appears to help measles spread widely."

"We also find that while 64 percent of infections may occur in children with a religious or personal vaccine exemption, 36 percent of cases occur in other members of the population: those unable to be vaccinated, those for whom the vaccine failed to provide immunity, and unvaccinated members of the population who are not school children. This supports the argument that individual choices to seek non-medical vaccine exemptions can have significant negative health outcomes for other people."

William Moss, a specialist in epidemiology and immunology at Johns Hopkins Bloomberg School of Public Health who did not work on the study, told Newsweek: "The study is significant because it provides insights into the size of potential measles outbreaks in the state of Texas resulting from vaccination exemptions for schoolchildren, using a sophisticated model and real data on populations and vaccination coverage."

He said it was "surprising" that only a 5 percent decrease in vaccination coverage was linked with a 40 to 4000 percent increase in potential outbreak size.

"We tend to think in terms of linear relationships, and thus that a 5 percent decrease in vaccination coverage might result in a 5 percent increase in potential outbreak size, but in fact the relationship is exponential. This is very important from a public health perspective: small decreases in measles vaccination coverage can have large consequences."

"They [the findings] show that vaccination exemptions for schoolchildren put not only these children at risk of measles but also susceptible people within the school or community within which they live," said Moss. "That is why vaccination is a broad public health good, benefiting not only the vaccinated child but the community."

This article has been updated with comment from Professor William Moss, and David Sinclair.