Infertility is a real risk, not a distant possibility.
Piracicaba region saw mumps cases rise from 387 to 538 annually, with 103 cases already recorded in early 2026, primarily affecting children under 14 years old. Declining MMR vaccine application across São Paulo state is linked to parental vaccine resistance, despite medical warnings of serious complications including potential infertility.
- Piracicaba mumps cases rose from 387 in 2024 to 538 in 2025—a 39% increase
- 103 cases recorded in first three months of 2026
- Most infections affect children and adolescents under 14 years old
- Campinas region saw 36.2% increase with 98 cases in early 2026
- MMR vaccine uptake declining across São Paulo state
Mumps cases in Piracicaba region jumped 39% to 538 in 2025, with most infections affecting children under 14, coinciding with declining MMR vaccine uptake across São Paulo state.
The pediatric wards across Piracicaba are filling with children complaining of swollen cheeks and fever. In the past year, the regional health system recorded 538 cases of mumps—a 39 percent jump from the 387 cases documented in 2024. The trend shows no sign of slowing. By March of this year, just three months into 2026, clinicians had already logged 103 new infections. Nearly all of them are children and adolescents under fourteen years old.
The surge is happening against a backdrop of collapsing vaccination rates. Across São Paulo state, fewer parents are bringing their children in for the MMR shot—the triple viral vaccine that has long been the standard defense against mumps, measles, and rubella. Health officials obtained the data through public records requests and found the same pattern repeating in neighboring regions. Campinas, another major city in the interior, reported a 36.2 percent increase in mumps cases over the same period, with 98 infections already documented this year.
Pediatrician Marianna Hufnagel points to vaccine hesitancy as the likely culprit. Some parents, she explains, have grown resistant to vaccinating their children—a shift that has left a generation increasingly vulnerable to a disease that most Brazilians had nearly forgotten. The medical community is alarmed not just by the rising case count, but by what mumps can do once it takes hold. The virus doesn't simply cause the characteristic swelling and discomfort. In boys, it can descend into the testicles; in girls, into the ovaries. The damage can be permanent. Infertility is a real risk.
Yet not all families have abandoned vaccination. Thaís Tardelli, an entrepreneur in the region, keeps her daughter Ayoluwa's immunization record meticulously current. At one year and nine months old, the child has received every scheduled vaccine on time. Tardelli credits her own mother's example—a household where health precautions were never negotiable. The same commitment shows up in other families. Seven-year-old João Pedro Lopes Giménez received both doses of the MMR vaccine, completing his series this week with the support of his parents, Letícia and Alexsander. The boy employed an unconventional coping strategy during the injections, shouting the name of his favorite soccer team to distract himself from the needle.
These pockets of compliance, however, are exceptions in a state where the overall trend is unmistakable. Health authorities are watching closely as the gap between vaccinated and unvaccinated children widens. The question now is whether the rising case count will shift parental attitudes, or whether mumps will continue its quiet return to a region that had learned to live without it.
Citações Notáveis
Mumps can descend into the testicles in boys and ovaries in girls, with risk of causing future infertility— Pediatrician Marianna Hufnagel
The rising infections may be linked to parental resistance to vaccinating children— Pediatrician Marianna Hufnagel
A Conversa do Hearth Outra perspectiva sobre a história
Why is mumps coming back now, after being so rare for so long?
Because fewer children are getting vaccinated. The MMR shot was so effective that mumps nearly disappeared—people forgot it was ever a threat. Now some parents are hesitant about vaccines, and immunity in the population is dropping.
But mumps is just swollen cheeks, right? Why are doctors so concerned?
That's the dangerous part of forgetting. Yes, it starts with swelling and fever. But in adolescents and young adults, it can move deeper—into the testicles or ovaries. The inflammation there can cause permanent damage. Infertility is a real outcome, not a scare tactic.
Are we talking about a lot of children, or is this still relatively small?
In Piracicaba alone, 538 cases in one year. That's a 39 percent jump. And it's only the beginning of 2026—already 103 cases in three months. Most are children under fourteen. In a region where mumps was nearly gone, that's significant.
What's driving the vaccine hesitancy? Is it distrust, or something else?
The reporting doesn't specify the exact reasons, but pediatrician Hufnagel points to parental resistance. It's part of a broader pattern of vaccine skepticism. Some families, though, are doing the opposite—keeping records current, getting both doses, making sure their children are protected.
Do those families know something the others don't?
They seem to understand that immunity is fragile. One mother credits her own upbringing—a household where health precautions were taken seriously. It's not complicated. It's just the habit of protection.