Childhood vaccination rates in the United States have seen a disturbing decline, particularly since the onset of the COVID-19 pandemic.
This drop in immunity levels has led to a resurgence of measles cases, including a significant outbreak in western Texas that infected more than 620 individuals, resulting in 64 hospitalizations and the tragic deaths of two children.
A new study from researchers at Stanford Medicine and other universities has raised alarms about what could happen if these immunization rates continue to fall over an extended period.
The findings suggest that diseases once considered eliminated, such as rubella and polio, could make a return to the U.S.
Published on April 24 in the Journal of the American Medical Association, the study employed large-scale epidemiological modeling to simulate the spread of infectious diseases in the United States under various childhood vaccination levels.
According to the researchers, even at current vaccination rates, measles may become endemic in the U.S. within the next two decades.
However, they also warn that small declines in vaccination could expedite this process, while even marginal increases in vaccine coverage would help prevent it.
Lead author Mathew Kiang, ScD, who is an assistant professor of epidemiology and population health, and senior author Nathan Lo, MD, PhD, an assistant professor of infectious diseases, hope their findings will inform vaccine policy decisions.
When asked why the research holds significant importance, Lo explained that measles is one of the most infectious diseases known to humankind.
To prevent its transmission, an exceptionally high percentage of the population must be immune.
While diseases like polio, diphtheria, and rubella are also highly infectious, measles stands out as one person can potentially infect up to 20 others, although the researchers’ model conservatively estimated 12 infections.
The controversy surrounding the MMR (measles, mumps, and rubella) vaccine partly stems from fraudulent medical research that raised safety concerns; however, it has been conclusively proven that there is no link between the vaccine and autism.
Additionally, because measles is still prevalent globally, travelers are more likely to carry it back to the U.S.
Kiang likened the situation to striking a match in a tinderbox — with under-vaccination acting as the tinder and travelers introducing the disease like matches.
He anticipated that a further decline in vaccination rates would have dire consequences.
If vaccination rates were to drop by even 10% today, Kiang projected that there would be approximately 11.1 million measles cases over the next 25 years.
In a more severe scenario where vaccination rates are halved, this would lead to 51.2 million measles cases, nearly 10 million cases of rubella, and 4.3 million polio cases, along with 200 cases of diphtheria over the same period.
Such an increase would result in about 10.3 million hospitalizations and an estimated 159,200 deaths.
The grim figures also include 51,200 children suffering from neurological complications due to measles, 10,700 cases of birth defects from rubella, and 5,400 people experiencing paralysis from polio.
In the scenario of a drop in vaccinations, measles could potentially become endemic in less than five years, while rubella could take less than two decades to reach similar status.
Even polio could become endemic in about half of the simulations performed, with a timeline of around 20 years.
The researchers also looked into the differences in vaccination coverage at the state level.
For instance, Massachusetts maintains high vaccination rates, placing it consistently at low risk.
Conversely, California and Texas are viewed as higher-risk states due to plummeting vaccination rates and considerable travel activity.
The model used in the study assumed there would not be a spillover of infections across state lines, indicating that the reported risks could be an underestimate.
In light of potentially widespread outbreaks, Lo noted that unvaccinated individuals are at the greatest risk of infection and severe complications.
This at-risk group includes infants aged 6 to 12 months, who have waning maternal antibodies but have not yet received their first dose of the MMR vaccine.
Individuals who are immunocompromised also face significant risks due to their vulnerability.
Complications arising from these diseases may soon become a reality for many clinicians, who have not had to contend with such issues thanks to decades of successful immunization efforts.
Lo posited that a plausible scenario could unfold where vaccine coverage continues to decline, leading to larger and more frequent measles outbreaks, ultimately resulting in the disease becoming endemic again.
He expressed hope that some unvaccinated individuals would seek vaccination in response to rising outbreaks and that public health departments would remain active in outbreak response efforts.
Such vigilance could help restore measles elimination in the U.S.
However, if changes to the childhood vaccination schedule are made and coverage decreases significantly, the fear of diseases like polio and rubella returning could manifest within a decade or longer.
Once these diseases reemerge, KIANG emphasized that eradication would not be instantaneous, explaining that it would require time to eliminate them once again.
Lo urged parents, healthcare providers, and policymakers to take action based on these insights.
He encouraged parents uncertain about vaccination to have discussions with their pediatricians and trust in healthcare experts.
Furthermore, the researchers aim their findings at federal and state officials, vaccine guideline committees, and other decision-makers to clearly illustrate the repercussions of declining vaccination rates.
Lo reiterated that even a 5% increase in vaccination rates could significantly reduce measles cases and slide the numbers safely away from endemic status.
This shows that small changes in vaccine coverage can have powerful impacts.
Kiang concluded by emphasizing that there should ideally be no cases of these preventable diseases, as any occurrence beyond zero is a tragedy.
The prospect of potentially thousands or millions of cases is unfathomable and urgent.
The research was supported by a grant from the National Institutes of Health, and additional contributors included experts from Baylor College of Medicine, Rice University, and Texas A&M University.
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