The cases in Kansas are likely part of the mushrooming outbreak that began in West Texas in late January. On March 13, Kansas reported a single measles case, the first the state had seen since 2018. The nine cases reported last week had ties to that original case.
Spreading infections and misinformation
On Wednesday, KDHE Communications Director Jill Bronaugh told Ars Technica over email that the department has found a genetic link between the first Kansas case and the cases in West Texas, which has similarly spread swiftly in under-vaccinated communities and also spilled over to New Mexico and Oklahoma.
“While genetic sequencing of the first Kansas case reported is consistent with an epidemiological link to the Texas and New Mexico outbreaks, the source of exposure is still unknown,” Bronaugh told Ars.
Bronaugh added that KDHE, along with local health departments, is continuing to work to track down people who may have been exposed to measles in affected counties.
In Texas, meanwhile, the latest outbreak count has hit 327 across 15 counties, mostly children and almost entirely unvaccinated. Forty cases have been hospitalized, and one death has been reported—a 6-year-old unvaccinated girl who had no underlying health conditions.
On Tuesday, The New York Times reported that as measles continues to spread, parents have continued to eschew vaccines and instead embraced “alternative” treatments, including vitamin A, which has been touted by anti-vaccine advocate and current US Health Secretary Robert F. Kennedy Jr. Vitamin A accumulates in the body and can be toxic with large doses or extended use. Texas doctors told the Times that they’ve now treated a handful of unvaccinated children who had been given so much vitamin A that they had signs of liver damage.
“I had a patient that was only sick a couple of days, four or five days, but had been taking it for like three weeks,” one doctor told the Times.
In New Mexico, cases are up to 43, with two hospitalizations and one death in an unvaccinated adult who did not seek medical care. In Oklahoma, officials have identified nine cases, with no hospitalizations or deaths so far.
Stat asked the HHS specifically about the Wild to Mild campaign as well as promotional campaigns for other vaccines, but an HHS spokesperson puzzlingly responded with a statement saying: “No, the CDC was not told to take down the flu vaccination campaign webpage,” which wasn’t what the outlet had asked about.
The statement went on to say: “Unfortunately, officials inside the CDC who are averse to Secretary Kennedy and President Trump’s agenda seem to be intentionally falsifying and misrepresenting guidance they receive.” NPR received the same statement.
Meanwhile on Thursday, The Washington Post reported that the HHS told the CDC to indefinitely postpone a meeting of its vaccine advisory committee (the Advisory Committee on Immunization Practices, or ACIP), which Kennedy has criticized. ACIP, comprised of independent experts, meets regularly to review and discuss vaccine safety and efficacy data and vote on recommendations.
ACIP was previously scheduled to meet February 26 to 28 to discuss a large number of vaccines, including those against meningitis, influenza, RSV, chikungunya, HPV, mpox, pneumococcal infections, Lyme disease, COVID-19, and CMV. An HHS spokesperson told the Post that the meeting was “postponed to accommodate public comment in advance of the meeting,” but there is no rescheduled date.
Leading medical experts and organizations, such as the American Medical Association, quickly sent a joint letter urging Kennedy to preserve the meeting. “Each ACIP meeting holds tremendous weight and relevance,” the letter states. ‘Infectious diseases are constantly evolving opponents; vaccines are among the best tools for constantly adapting and responding to the latest public health threats. … Making America healthy requires healthy discussion and timely, evidence-based decisions. This meeting should be no different.”
In an interview with Ars Technica last week, Zach Holbrooks, the executive director of the South Plains Public Health District (SPPHD), which includes Gaines, said that the area has a large religious community that has expressed vaccine hesitancy.
Additional cases likely
Pockets of the county have yet lower vaccination rates than the county-wide averages suggest. For instance, one independent public school district in Loop, in the northeast corner of Gaines, had a vaccination rate of 46 percent in the 2023–2024 school year.
Measles is one of the most infectious diseases known. The measles virus spreads through the air and can linger in the airspace of a room for up to two hours after an infected person has left. Ninety percent of unvaccinated people who are exposed will fall ill with the disease, which is marked by a very high fever and a telltale rash. Typically, 1 in 5 unvaccinated people with measles in the US end up hospitalized, and 1 in 20 develop pneumonia. Between 1 to 3 in 1,000 die of the infection. In rare cases, it can cause a fatal disease of the central nervous system called Subacute sclerosing panencephalitis later in life. Measles can also wipe out immune responses to other infections (a phenomenon known as immune amnesia), making people vulnerable to other infectious diseases.
“Due to the highly contagious nature of this disease, additional cases are likely to occur in Gaines County and the surrounding communities,” the state health department said.
While Gaines is remarkable for its low vaccination rate, vaccination coverage nationwide has slipped in recent years as vaccine misinformation and hesitancy have taken root. Overall, vaccination rates among US kindergartners have fallen from 95 percent in the 2019–2020 school year into the 92 percent range in the 2023–2024 school year. Vaccine exemptions, meanwhile, have hit an all-time high. Health experts expect to see more vaccine-preventable outbreaks, like the one in Gaines, as the trend continues.
As federal lawmakers prepare to decide whether anti-vaccine advocate Robert F. Kennedy Jr. should be the next secretary of the Department of Health and Human Services, pediatricians from around the country are making emotional pleas to protect and support lifesaving immunizations.
The American Academy of Pediatrics (AAP) has assembled nearly 200 stories and dozens of testimonials on the horrors of vaccine-preventable deaths and illnesses that pediatricians have encountered over their careers. The testimonials have been shared with two Senate committees that will hold hearings later this week: the Senate Committee on Finance and the Senate Committee on Health, Education, Labor, and Pensions (HELP).
“I remember that baby’s face to this day”
In a statement on Monday, AAP President Susan Kressly noted that the stories come from a wide range of pediatricians—from rural to urban and from small practices to large institutions. Some have recalled stories of patients who became ill with devastating diseases before vaccines were available to prevent them, while others shared more recent experiences as vaccine misinformation spread and vaccination rates slipped.
In one, a pediatrician from Raleigh, North Carolina, spoke of a baby in the 1990s with Streptococcuspneumoniae meningitis, a life-threatening disease. “I remember holding a baby dying of complications of pneumococcal meningitis at that time. I remember that baby’s face to this day—but, thanks to pneumococcal vaccination, have never had to relive that experience since,” the doctor said. The first pneumococcal vaccine for infants was licensed in the US in 2000.
A doctor in Portland, Maine, meanwhile, faced the same disease in a patient who was unvaccinated despite the availability of the vaccine. “As a resident, I cared for a young, unvaccinated child admitted to the pediatric intensive care unit with life-threatening Streptococcus pneumoniae meningitis. This devastating illness, once common, has become rare thanks to the widespread use of pneumococcal conjugate vaccines. However, this child was left vulnerable…and [their parents] now faced the anguish of watching their child fight for their life on a ventilator.”
Kressly emphasizes that “One unifying theme of these stories: vaccines allow children to grow up healthy and thrive. As senators consider nominees for federal healthcare agencies, we hope these testimonies will help paint a picture of just how important vaccinations are to children’s long-term health and wellbeing.”
Their investigative report—based on interviews with multiple health department employees who spoke on the condition of anonymity for fear of retaliation—revealed that employees were told of the startling policy change in meetings in October and November and that the policy would be implemented quietly and not put into writing.
Ars Technica has contacted the health department for comment and will update this post with any new information.
The health department provided a statement to NPR saying that it has been “reevaluating both the state’s public health priorities as well as our messaging around vaccine promotion, especially for COVID-19 and influenza.” The statement described the change as a move “away from one-size-fits-all paternalistic guidance” to a stance in which “immunization for any vaccine, along with practices like mask wearing and social distancing, are an individual’s personal choice.”
According to employees, the new policy cancelled standard fall flu vaccination events this year and affects every other aspect of the health department’s work, as NPR explained:
“Employees could not send out press releases, give interviews, hold vaccine events, give presentations or create social media posts encouraging the public to get the vaccines. They also could not put up signs at the department’s clinics that COVID, flu or mpox vaccines were available on site.”
“We’re really talking about deaths”
The change comes amid a dangerous swell of anti-vaccine sentiment and misinformation in Louisiana and across the country. President-elect Trump has picked Robert F. Kennedy Jr.—a high-profile anti-vaccine advocate and one of the most prolific spreaders of vaccine misinformation—to head the US Department of Health and Human Services.
Earlier this week, Robert F. Kennedy, Jr. used a Zoom call to tell his supporters that Donald Trump had promised him “control” of the Department of Health and Human Services (HHS), the federal agency that includes the Centers for Disease Control, Food and Drug Administration, National Institutes of Health, as well as the Department of Agriculture. Given Kennedy’s support for debunked anti-vaccine nonsense, this represents a potential public health nightmare.
A few days after, Howard Lutnick, a co-chair of Trump’s transition team, appeared on CNN to deny that RFK Jr. would be put in charge of HHS. But he followed that with a long rant in which he echoed Kennedy’s spurious claims about vaccines. This provides yet another indication of how anti-vaccine activism has become deeply enmeshed with Republican politics, to the point where it may be just as bad even if Kennedy isn’t appointed.
Trump as Kennedy’s route to power
Kennedy has a long history of misinformation regarding health, with a special focus on vaccines. This includes the extensively debunked suggestion that there is a correlation between vaccinations and autism incidence, and it extends to a general skepticism about vaccine safety. That’s mixed with conspiracy theories regarding collusion between federal regulators and pharmaceutical companies.
While there is no evidence for any of this, and some of it is clearly wrong, the conspiracies have real-world consequences. An anti-vaccine activist in Samoa, aided by a visit from RFK Jr., helped pave the way for a measles outbreak that shut down the government and ultimately led to over 80 deaths.
Kennedy has long been interested in getting access to the agencies that regulate vaccines and other interests of his, such as food safety, under the assumption they are hiding the data that would vindicate his views. And, long before his recent presidential run, he viewed Trump as the route to that access. Shortly before Trump’s inauguration in 2017, Kennedy claimed that he would be appointed to head a vaccine safety commission that Trump would supposedly create once in office. Nothing ever came of that, and it was never clear whether that was due to Trump lying to him, Kennedy exaggerating his significance, or Trump simply telling him what he wanted to hear at the time and never following up.
In the hearing, board member Jennifer Riebe (who voted to keep COVID-19 vaccinations available) worried about the potential of a slippery slope.
“My concern with this is the process because if this board and six county commissioners and one physician is going to make determinations on every single vaccine and pharmaceutical that we administer, I’m not comfortable with that,” she said, according to Boise State Public Radio. “It may be COVID now, maybe we’ll go down the same road with the measles vaccine or the shingles vaccine coverage.”
Board Chair Kelly Aberasturi, who also voted to keep the vaccines, argued that it should be a choice by individuals and their doctors, who sometimes refer their patients to the district for COVID shots. “So now, you’re telling me that I have the right to override that doctor? Because I know more than he does?” Aberasturi said.
“It has to do with the right of the individual to make that decision on their own. Not for me to dictate to them what they will do. Sorry, but this pisses me off,” he added.
According to Boise State Public Radio, the district had already received 50 COVID-19 vaccines at the time of the vote, which were slated to go to residents of a skilled nursing facility.
The situation in the southwest district may not be surprising given the state’s overall standing on vaccination: Idaho has the lowest kindergarten vaccination rates in the country, with coverage of key vaccinations sitting at around 79 percent to 80 percent, according to a recent analysis by the Centers for Disease Control and Prevention. The coverage is far lower than the 95 percent target set by health experts. That’s the level that would block vaccine-preventable diseases from readily spreading through a population. The target is out of reach for Idaho as a whole, which also has the highest vaccination exemption rate in the country, at 14.3 percent. Even if the state managed to vaccinate all non-exempt children, the coverage rate would only reach 85.7 percent, missing the 95 percent target by nearly 10 percentage points.
Enlarge/ A US child infected with measles during a 2024 outbreak. The child’s cheek shows the characteristic rash associated with this viral infection.
With one of the highest vaccine exemption rates in the country, Oregon is experiencing its largest measles outbreak in decades. This year’s count is now higher than anything seen since 2000, when the Centers for Disease Control and Prevention declared the highly contagious virus eliminated from the US.
Last month, when the outbreak tally was still in the 20s, health officials noted that it was nearing a state record set in 2019. There were 28 cases that year, which were linked to a large outbreak across the border in Washington state. But, with that record now surpassed, the state is in pre-elimination territory.
“Before 2019, you have to go all the way back to the early 1990s to see case counts this high,” Paul Cieslak, medical director for communicable diseases and immunization at Oregon Health Authority, said in a statement. “The reason is, we maintained very high vaccination rates and very high population levels of immunity. Unfortunately, we’ve seen an erosion in the percentage of people who are getting vaccinated against measles.”
Vaccination decline
In 2000, when measles was declared officially eliminated, only about 1 percent of kindergarteners in the state had exemptions from childhood vaccines, such as measles. But in the years since, Oregon has become one of the states with the highest exemption rates in the country. In the 2022–2023 school year, 8.2 percent of Oregon kindergarteners had exemptions from vaccinations, according to a CDC analysis published in November. Only Idaho had a higher rate, with 12.1 percent of kindergarteners exempt. Utah was a close third, with 8.1 percent, followed by Arizona (7.4 percent) and Wisconsin (7.2 percent).
Oregon’s exemption rate has risen since then, with the exemption rate now at 8.8 percent, according to the Oregon Health Authority. Any exemption rate above 5 percent is concerning. At that threshold, even if every non-exempt child is vaccinated, a state will not be able to achieve the target of 95 percent vaccine coverage expected to prevent sustained transmission of infectious diseases.
Health officials are directly linking the rise of non-medical exemptions to the current measles outbreak, which is centered in Clackamas, Marion, and Multnomah counties. All three are in the northwestern corner of the state, with Clackamas and Multnomah in the Portland area.
“In Clackamas County, as in other Oregon counties, pockets of unvaccinated people raise risk of infection in communities where they live,” Clackamas County Health Officer Sarah Present said. “That’s why the counties reach out to every case that’s been identified and try to determine exactly where they’ve been while infectious.”
Notorious virus
Measles is among the most infectious viruses known. It is notorious for its ability to stay aloft in indoor air for up to two hours after an infected person has been present. For unvaccinated people who are exposed, up to 9 out of 10 will end up falling ill. Those who become infected are contagious from about four days before developing the tell-tale rash and four days after it erupts. Other common symptoms of the infection include high fever, runny nose, cough, and conjunctivitis (pink eye). Many children become severely ill, requiring hospitalization.
In a small percentage of cases, measles can lead to severe complications, including pneumonia, encephalitis, and a progressive neurological disorder (subacute sclerosing panencephalitis), which develops five to 10 years after an initial infection. Additionally, measles is known to cause “immune amnesia.” That is, being infected with measles virus wipes out existing antibodies and immune responses to other germs, leaving people more vulnerable to other diseases.
So far this year, the US has logged 236 measles cases. Of those, 40 percent were in children under the age of 5, while 30 percent were in children and teens between the ages 5 and 19. Eighty-seven percent were either unvaccinated or had an unknown vaccination status. Forty-four percent (103 of 236) were hospitalized.
This year’s tally is already well ahead of the total for 2023, which reached just 59 cases. It is still significantly lower than the 1,274 cases seen in 2019, when the US nearly lost its elimination status.
Enlarge/ A 13-year-old celebrates getting the Pfizer-BioNTech COVID-19 vaccine in Hartford, Connecticut, on May 13, 2021.
With the impending arrival of the 2024–2025 COVID-19 vaccines approved yesterday, some Americans are now gaming out when to get their dose—right away while the summer wave is peaking, a bit later in the fall to maximize protection for the coming winter wave, or maybe a few weeks before a big family event at the end of the year? Of course, the group pondering such a question is just a small portion of the US.
In a press briefing Friday, federal health officials were quick to redirect focus when reporters raised questions about the timing of COVID-19 vaccination in the coming months and the possibility of updating the vaccines twice a year, instead of just once, to keep up with an evolving virus that has been producing both summer and winter waves.
“The current problem is not that the virus is evolving so much, at least in terms of my estimation,” Peter Marks, the top vaccine regulator at the Food and Drug Administration, told journalists. “It’s that we don’t have the benefits of the vaccine, which is [to say] that it’s not vaccines that prevent disease, it’s vaccination. It’s getting vaccines in arms.” When exactly to get the vaccine is a matter of personal choice, Marks went on, but the most important choice is to get vaccinated.
Estimates for this winter
The press briefing, which featured several federal health officials, was intended to highlight the government’s preparations and hopes for the upcoming respiratory virus season. The FDA, the Centers for Disease Control and Prevention, and the Department of Health and Human Services (HHS) are urging all Americans to get their respiratory virus vaccines—flu, COVID-19, and RSV.
CDC Director Mandy Cohen introduced an updated data site that provides snapshots of local respiratory virus activity, national trends, data visualizations, and the latest guidance in one place. HHS, meanwhile, highlighted a new outreach campaign titled “Risk Less. Do More.” to raise awareness of COVID-19 and encourage vaccination, particularly among high-risk populations. For those not at high risk, health officials still emphasize the importance of vaccination to lower transmission and prevent serious outcomes, including long COVID. “There is no group without risk,” Cohen said, noting that the group with the highest rates of emergency department visits for COVID-19 were children under the age of 5, who are not typically considered high risk.
So far, CDC models are estimating that this year’s winter wave of COVID-19 will be similar, if not slightly weaker on some metrics, than last year’s winter wave, Cohen said. But she emphasized that many assumptions go into the modeling, including how the virus will evolve in the near future and the amount of vaccine uptake. The modeling assumes the current omicron variants stay on their evolutionary path and that US vaccination coverage is about the same as last year. Of course, beating last year’s vaccine coverage could blunt transmission.
As the COVID-19 case count continues to tick upward, the US Food and Drug Administration has approved an updated vaccine for use ahead of the northern hemisphere winter. The emergency use authorization covers updated mRNA vaccines from both Pfizer and Moderna.
The booster shots will target the JN.1 and KP.2 strains of SARS-CoV-2, both of which are omicron variants. Last year’s booster keyed on omicron subvariant XBB.1.5, which has long since lost the evolutionary arms race.
Both Spikevax (Moderna) and Comirnaty (Pfizer) vaccines have been updated. While the vaccine is targeted toward those 12 and over, parents of children aged six months through 11 years are also eligible for the updated vaccines under the FDA’s emergency use authorization.
“Vaccination continues to be the cornerstone of COVID-19 prevention,” said Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research. “These updated vaccines meet the agency’s rigorous, scientific standards for safety, effectiveness, and manufacturing quality. Given waning immunity of the population from previous exposure to the virus and from prior vaccination, we strongly encourage those who are eligible to consider receiving an updated COVID-19 vaccine to provide better protection against currently circulating variants.”
Updated vaccines will hit hospitals and pharmacies soon, as Moderna and Pfizer are ready to ship vaccines. Once injected, the boosters will take a couple of weeks to hit peak protection, and they will offer that level of protection for a few months after the shot. Keep that in mind as you think about timing your booster for maximum efficacy.
Enlarge/ Polio victim Larry Montoya is at the airport for the arrival of cases of vaccine, which were distributed as part of the KO Polio campaign, September 5, 1962.
Public sentiment on the importance of safe, lifesaving childhood vaccines has significantly declined in the US since the pandemic—which appears to be solely due to a nosedive in support from people who are Republican or those who lean Republican, according to new polling data from Gallup.
In 2019, 52 percent of Republican-aligned Americans said it was “extremely important” for parents to get their children vaccinated. Now, that figure is 26 percent, falling by half in just five years. In comparison, 63 percent of Democrats and Democratic leaners said it was “extremely important” this year, down slightly from 67 percent in 2019.
Overall, only 40 percent of Americans now say it is extremely important for parents to vaccinate their children, down from 58 percent in 2019 and 64 percent in 2001.
More broadly, 93 percent of the Democratic group said it was “extremely” or “very” important for parents to vaccinate their children this year, while only 52 percent of the Republican group said the same.
On the other end of the spectrum, 11 percent of the Republican group said vaccinating children was “not important at all,” and an additional 8 percent said it was “not very important.” For the Democratic group, only 1 percent was reported in each of those categories.
Dangerous disinformation
Perhaps most concerning, the data indicated that a growing number of Americans view vaccines as more dangerous than the diseases they prevent—including polio, measles, tetanus, rotavirus, diphtheria, whooping cough, meningitis, and RSV, among others. Now, 20 percent of Americans overall think vaccines are more of a threat than the dangerous diseases they effectively prevent.
The partisan divide is most stark on this sentiment. In 2019, the two parties were about the same. Twelve percent of the Republican group and 10 percent of the Democratic group held this erroneous belief. But now, a whopping 31 percent of the Republican group say vaccines are a more significant threat than dangerous diseases, while the percentage among the Democratic group fell to 5 percent.
Republicans and Republican leaners are much more likely than Democrats and Democratic leaners to believe the false and debunked claim that vaccines are linked to autism—19 percent of the Republican group believe this falsehood compared to 4 percent of the Democratic group.
The polling data aligns with national vaccination trends tracked by the Centers for Disease Control and Prevention. During the pandemic, rates of routine vaccination among kindergartners slipped from the protective target of 95 percent—which prevents infectious diseases from spreading widely—to 93 percent. Additionally, nonmedical exemptions from vaccinations have reached an all-time high of 3 percent nationally. At least 10 states have exemption rates at or above 5 percent, preventing them from reaching the protective target of 95 percent vaccination coverage.
Enlarge/ A view from a hospital as children receiving medical treatment, in capital Kabul, Afghanistan on April 18, 2022. More than 130 children have died from the measles in Afghanistan since the beginning of this year.
The Centers for Disease Control and Prevention and the American Medical Association sent out separate but similar pleas on Monday for unvaccinated Americans to get vaccinated against the extremely contagious measles virus as vaccination rates have slipped, cases are rising globally and nationally, and the spring-break travel period is beginning.
In the first 12 weeks of 2024, US measles cases have already matched and likely exceeded the case total for all of 2023. According to the CDC, there were 58 measles cases reported from 17 states as of March 14. But media tallies indicate there have been more cases since then, with at least 60 cases now in total, according to CBS News. In 2023, there were 58 cases in 20 states.
“As evident from the confirmed measles cases reported in 17 states so far this year, when individuals are not immunized as a matter of personal preference or misinformation, they put themselves and others at risk of disease—including children too young to be vaccinated, cancer patients, and other immunocompromised people,” AMA President Jesse Ehrenfeld said in a statement urging vaccination Monday.
The latest data indicates that vaccination rates among US kindergarteners have slipped to 93 percent nationally, below the 95 percent target to prevent the spread of the disease. And vaccine exemptions for non-medical reasons have reached an all-time high.
The CDC released a health advisory on Monday also urging measles vaccination. The CDC drove home the point that unvaccinated Americans are largely responsible for importing the virus, and pockets of unvaccinated children in local communities spread it once it’s here. The 58 measles infections that have been reported to the agency so far include cases from seven outbreaks in seven states. Most of the cases are in vaccine-eligible children aged 12 months and older who are unvaccinated. Of the 58 cases, 54 (93 percent) are linked to international travel, and most measles importations are by unvaccinated US residents who travel abroad and bring measles home with them, the CDC flagged.
The situation is likely to worsen as Americans begin spring travel, the CDC suggested. “Many countries, including travel destinations such as Austria, the Philippines, Romania, and the United Kingdom, are experiencing measles outbreaks,” the CDC said. “To prevent measles infection and reduce the risk of community transmission from importation, all US residents traveling internationally, regardless of destination, should be current on their [measles-mumps-rubella (MMR)] vaccinations.” The agency added in a recommendation to parents that “even if not traveling, ensure that children receive all recommended doses of MMR vaccine. Two doses of MMR vaccine provide better protection (97 percent) against measles than one dose (93 percent). Getting MMR vaccine is much safer than getting measles, mumps, or rubella.”
For Americans who are already vaccinated and communities with high vaccination coverage, the risk is low, the CDC noted. “However, pockets of low coverage leave some communities at higher risk for outbreaks.” This, in turn, threatens wider, continuous spread that could overturn the country’s status of having eliminated measles, which was declared in 2000. The US was close to losing its elimination status in 2019 when outbreaks among unvaccinated children drove 1,247 cases across 31 states. Vaccination rates have only fallen since then.
“The reduction in measles vaccination threatens to erase many years of progress as this previously eliminated vaccine-preventable disease returns,” the AMA’s Ehrenfeld warned.
As Ars has reported previously, measles is among the most contagious viruses known and can linger in airspace for up to two hours. Up to 90 percent of unvaccinated people exposed will contract it. Symptoms can include high fever, runny nose, red and watery eyes, and a cough, as well as the hallmark rash. About 1 in 5 unvaccinated people with measles are hospitalized, while 1 in 20 infected children develop pneumonia, and up to 3 in 1,000 children die of the infection. Brain swelling (encephalitis) can occur in 1 in 1,000 children, which can lead to hearing loss and intellectual disabilities. The virus can also destroy immune responses to previous infections—a phenomenon known as “immune amnesia”—which can leave children vulnerable to various other infections for years afterward.
