Daniel Pastula, University of Colorado Anschutz Medical Campus

The measles outbreak that started in Texas in late January continues to grow. As of March 18, 2025, confirmed cases in the outbreak, which now spans Texas, New Mexico and Oklahoma, reached 321, surpassing the number of confirmed cases recorded for all of the U.S. in 2024. The vast majority of cases are in people who are not vaccinated. Meanwhile, a lack of clarity from health authorities is leaving people with questions about whether they need to get revaccinated.

In a Q&A with The Conversation U.S., Daniel Pastula, a neurologist and medical epidemiologist from the University of Colorado Anschutz Medical Campus and Colorado School of Public Health, explained how and when you should take action.

Should adults get another shot of the measles vaccine?

The measles vaccine, which first became available in the U.S. in 1963, contains a live but significantly weakened strain of the measles virus. This modified strain is too weak to cause measles, but it is similar enough to the wild type measles virus to train the immune system to recognize it. Most people who have received the live measles vaccine won’t need an additional shot now, but here is what you need to know:

People born before 1957 are presumed to have lifelong immunity because measles was so contagious that almost everyone contracted it before age 15. Unless there are special circumstances, they probably don’t need a vaccine now.

Most people born after 1957 would have received the shot as children, so they should be set for life. Physicians and public health experts don’t recommend most people in this group get a second measles shot, though there are exceptions.

In 1989, a limited outbreak of measles occurred among vaccinated school children. In response, the recommendations changed from one dose of the live measles vaccine to two doses for children. People fully vaccinated as children after that year do not need any additional doses.

Exceptions to these guidelines

There are two special circumstances where the previous recommendations may not hold.

First, if you were vaccinated between 1963 and 1967, one of the measles vaccines available at the time consisted of just proteins from the virus rather than a live, weakened version of it. Researchers soon realized this inactivated, or “killed,” vaccine was less effective and didn’t provide long-term immunity. Unless you know for certain you received the live vaccine, physicians and public health experts recommend that people vaccinated during those years get one dose of the live vaccine at some point.

Second, if you fall into a high-risk group – for example, if you are a health care provider, are traveling internationally or attending college, physicians and public health experts generally recommend getting a second dose if you have only had one.

For most adults without such risk factors, physicians and public health experts do not routinely recommend a second dose if you have previously received one dose of a live measles vaccine. If you have questions or concerns about your situation, make sure to ask your health care provider.

Except in very rare circumstances, there is no recommendation for a third dose of the measles vaccine.

Can you find out whether you’ve been vaccinated?

You might be able to! It’s worth checking. States actually keep vaccine records specifically for this reason, where you can look up your vaccine records or that of your kids. Your high school or college may still have your records, and so might your pediatrician’s office.

Should you get your antibody levels checked?

For most people, probably not.

A titer test checks the level of antibodies in your blood, and some people are asking their doctor to check their titers to determine whether they are still immune to measles. The problem is, the level of antibodies in your blood does not necessarily reflect your level of immunity. That’s because antibodies are just one part of your immune system’s infection-fighting force. Having a low level of antibodies does not necessarily mean your immunity has waned.

Other crucial elements of your immune response include B cells, T cells and other immune cells, but a titer test does not show their capabilities. For example, memory B cells might not currently be making antibodies against the virus but are primed to quickly do so the next time they see it. This is why antibody and titer tests should be used only in specific cases, in consultation with your doctor.

One example of when an antibody test may be warranted is if you are a health care provider born before 1957 and you want to make sure you don’t need another dose of the vaccine. You would use a test to see whether you have measles antibodies. But in this case you would be looking for a yes or no answer; the total amount of antibodies may not be very informative.

Is natural immunity better than vaccine-induced immunity?

Natural immunity – that is, the immunity you get after having measles – is effective. However, the downside is that natural infection with a wild virus is very risky. Before 1963, measles caused close to 50,000 hospitalizations and about 500 deaths each year in the United States, usually in children. It also caused over 1,000 cases of severe brain inflammation every year and carried several other long-term risks, such as permanent hearing loss or the wipe out of immunity to other diseases.

The point of vaccines is to create immunity without the risks of severe infection. It is basically a dress rehearsal for the real thing. The immunity from a vaccine is effectively the same immunity you get from having measles itself – but vastly safer than encountering the wild virus unprotected. One dose is 93% effective at preventing measles and two doses are 97% effective, and any breakthrough cases are likely to be much milder than a full-blown case of measles.

Can the vaccine cause measles?

No, the measles vaccine cannot cause measles because it contains a significantly weakened strain that has limited ability to infect and damage cells.

Some have claimed without evidence that the current outbreak in Texas was caused by the measles vaccine.

As part of the outbreak investigation, however, CDC and the Texas Department of State Health Services analyzed the genome of the virus causing the current outbreak and identified it as a wild measles virus. Researchers classify measles virus strains based on their genetic characteristics, or genotypes. They identified the outbreak virus as wild type genotype D8, and not the weakened measles vaccine strain, which is genotype A.

What are the risks of the vaccine?

That is a very reasonable question. Because the measles vaccine is a live, weakened virus strain, it can cause a mild, measles-like syndrome. For example, some people might have a slight fever, a rash, or some slight joint pain. These symptoms generally go away in a day or two, and most people don’t experience them. But the vaccine cannot cause measles itself, as it does not contain the wild measles virus.

In extremely rare cases, people can experience more significant reactions to the measles vaccine. It is important to remember that every single medical or health intervention carries risks – and that includes all medications and over-the-counter supplements. According to all available evidence, however, comparing the potential benefits against potential risks reveals that the risks of a signficant reaction to the vaccine are much lower than the risks of severe outcomes from measles itself.

Being vaccinated not only protects you and your family, but it also protects vulnerable people in the community, such as infants, cancer patients and pregnant women, who cannot be vaccinated themselves.

Daniel Pastula, Professor of Neurology, Medicine (Infectious Diseases), and Epidemiology, University of Colorado Anschutz Medical Campus

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Eli Elster, University of California, Davis

Of the 8.7 million species on Earth, why are human beings the only one that paints self-portraits, walks on the Moon and worships gods?

For decades, many scholars have argued that the difference stems from our ability to learn from each other. Through techniques such as teaching and imitation, we can create and transmit complicated information over many generations.

So if a human finds, for instance, a better but more complex way to make a knife, they can pass along the new instructions. One of those learners might stumble upon their own improvement and pass it along in turn.

If this loop continues, you get a ratchet effect, in which small changes can accumulate over time to produce increasingly intricate behaviors and technologies. This process produces our uniquely complex cultures: Scientists call it cumulative cultural evolution.

But extensive data has emerged suggesting that other animals, including bees, chimpanzees and crows, can also generate cultural complexity through social learning. Consequently, the debate over human uniqueness is shifting in a new direction.

As an anthropologist, I study a different feature of human culture that researchers are beginning to think about: the diversity of our traditions. Whereas animal cultures affect just a few crucial behaviors, such as courtship and feeding, human cultures cover a massive and constantly expanding set of activities, from clothing to table manners to storytelling.

This new view suggests that human culture is not uniquely cumulative. It is uniquely open-ended.

What is cumulative culture?

In the early 2000s, a research team led by psychologist Michael Tomasello tested 105 human children, 106 adult chimpanzees and 32 adult orangutans on a battery of cognitive assessments. Their goal was to see whether humans held any innate cognitive advantage over their primate cousins.

Surprisingly, the human children performed better in only one capacity: social learning. Tomasello thus concluded that humans are not “generally smarter.” Rather, “we have a special kind of smarts.” Our advanced social abilities allow us to transmit information by accurately teaching and learning from each other.

Humans’ apparent social learning abilities suggested a clear explanation for our unique cultural traits. Knowledgeable humans – say, someone who discovers a better way to make a spear – can successfully transfer that skill to their peers. But an inventive chimp – one who discovers a better way to smash nuts, for example – can’t successfully share their innovation. Nobody listens to Chimp Einstein. So our inventions persist and build upon each other, while theirs vanish into the jungle floor.

Or so the theory went.

Now, though, scientists have hard evidence showing that, just like us, animals can learn from each other and thus maintain their cultures for long periods of time. Groups of swamp sparrows appear to use the same song syllables for centuries. Meerkat troops settle on different wake-up times and maintain them for a decade or more.

Of course, long-term social learning is not the same as cumulative culture. Yet scientists also now know that humpback whale songs can oscillate in complexity over many generations of learners, that homing pigeons create efficient flight paths by learning from each other and making small improvements, and that hooved mammals cumulatively alter their migration routes to exploit plant growth.

Once again, the animals have shot down our claim to uniqueness, as they have innumerable times throughout scientific history. You might wonder, at this point, if we should just settle the uniqueness question by answering: “We’re not.”

If not cumulative culture, what makes us unique?

But it remains the case that humans and their cultures are quite different from animals and their equivalents. Most scholars agree about that, even if they disagree about the reasons why. Since cumulative complexity appears not to be the most important difference, several researchers are sketching out a new perspective: Human culture is uniquely open-ended.

Currently, anthropologists are discussing open-endedness in two related ways. To get a sense of the first, try counting the number of things you’re engaged with, right now, that came to you through culture. For example, I picked my clothes today based on fashion trends I did not develop; I am writing in a language I did not invent; I tied my shoes using a method my father taught me; there are paintings and postcards and photographs on my walls.

Give me 10 minutes, and I could probably add 100 more items to that list. In fact, other than biological acts such as breathing, it is difficult for me to think of any aspect of what I’m doing right now that is not partially or completely cultural. This breadth is incredibly strange. Why should any organism spend time pursuing such a wide range of goals, particularly if most of them have nothing to do with survival?

Other animals are much more judicious. Their cultural variation and complexity pertains almost entirely to matters of subsistence and reproduction, such as acquiring food and mating. Humans, on the other hand, lip-synch, build space stations and, less grandiosely, have been known to do things such as spend six years trying to park in all 211 spots of a grocery store lot. Our cultural diversity is unparalleled.

Open-endedness, as a unique human quality, is not just about variety; it reflects the quantum leaps by which our cultures can evolve. To illustrate this peculiarity, consider a hypothetical example regarding the rocks that chimpanzees use to smash nuts.

Let’s say these chimps would benefit from using rocks that they can swing as hard and accurately as possible, but that they don’t immediately know what kind of rocks those would be. By trying different options and observing each other, they might accumulate knowledge of the best qualities in a nut-smashing rock. Eventually, though, they’d hit a limit in the power and precision available by swinging a rock with your fist.

How could they get past this upper limit? Well, they could tie a stick to their favorite rock; the extra leverage would help them smash the nuts even harder. As far as we know, though, chimpanzees aren’t capable of realizing the benefits of harnessing this additional quality. But we are – people invented hammers.

Crucially, discovering the power of leverage allows for more than just better nut-smashing. It opens up innovations in other domains. If adding handles to wielded objects allows for better nut-smashing, then why not better throwing, or cutting, or painting? The space of cultural possibilities, suddenly, has expanded.

Through open-ended cultural evolution, human beings produce open-endedness in culture. In this respect, our species is unparalleled.

What’s next?

Researchers have not yet answered most of the major questions about open-endedness: how to quantify it, how we create it, whether it has any true limitations.

But this new framework must shift the tides of a related debate: whether there is something obviously different about the way human minds work, other than social learning capacities. After all, every cultural trait emerges through interactions between minds – so how do our minds interact to produce such a degree of cultural breadth?

No one knows yet. Interestingly, this shifting debate over how cognition influences culture coincides with a spate of research bridging psychology and anthropology, which explores why certain behaviors – such as singing lullabies, curative bloodletting and storytelling – recur across human cultures.

Human minds produce unparalleled diversity in their cultures; yet it is also true that those cultures tend to express variations on a strict set of themes, such as music and marriage and religion. Ironically, the source of our open-endedness may illuminate not only what makes us so diverse, but also what makes us so often the same.

Eli Elster, Doctoral Candidate in Evolutionary Anthropology, University of California, Davis

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Lori Frasier, Penn State

In the early 1990s when I was a young pediatrician, I was responsible for evaluating children with developmental and learning problems. Two unrelated boys, ages 7 and 9, were found to have IQs in the range of 60-70, which indicates a severe cognitive disability.

During my medical review, the mothers revealed that their children were shaken violently as infants and that afterward behaved as if “the wind had been knocked out of them.” Both mothers reported shaking by a boyfriend or a father. No child was seen for medical care at the time.

At the same period of my career I was working with a renowned pediatrician who was studying shaken baby syndrome. The link between shaking and later cognitive impairment was not lost on me.

This scenario of shaken babies having neurological and developmental disabilities has played out over the past 30 years of my career as a child abuse pediatrician.

The high rates of death and disability

Shaken baby syndrome is a condition that can injure babies and young children, and in some cases lead to death.

A 2024 study on babies with shaken baby syndrome found that 20% to 25% of infants die, another 20% to 25% look normal on discharge from the hospital, and fully half are left with long-term disabilities. These include learning and behavioral problems that appear later in life.

The dangers of shaking babies have been recognized for over 50 years.

In the early 1970s, John Caffey, a pediatric radiologist, coined the term “Whiplash Shaken Infant Syndrome.” Caffey linked permanent brain damage and bleeding in the backs of the retina to violent shaking of infants. Caffey suggested a multipronged approach to prevention of this severe form of abuse that included educating and supporting young families, especially mothers. As primary caregivers, mothers are often most easily reached by the message, but the message of prevention can involve fathers, babysitters and any other caregivers.

Since Caffey’s original description, there have been tremendous advancements in the research behind shaking babies and infant head trauma. In 2009, the American Academy of Pediatrics recommended that medical providers use the term “abusive head trauma” to include many actions other than shaking that can injure the brains of infants and children. The use of shaken baby syndrome is still recommended for public education and prevention, and health care providers and other experts also recommend the use of the term because it’s commonly recognized by the lay public and understood by parents.

How the brain is affected

What happens to the brain of an infant when they are shaken?

Infants – the most common population to be shaken – are small and have undeveloped neck muscles.

In these incidents, the infant is typically grabbed around the chest and shaken back and forth several times. Small blood vessels around the brain break and bleed, causing blood to flow around the brain. This condition is called a subdural hematoma. In some cases, similar forces occur in the back of the eye, and hemorrhages in the retina can occur.

In the most severe forms of shaking, the tissue of the brain itself is injured, and the child may experience unconsciousness or even stop breathing. Neck injuries occur when shaking causes injuries to ligaments and muscles that support the neck. Sometimes children have other injuries after being thrown down or impacted against something. Skull fractures or fractures of other bones, bruising and other injuries are often found.

A complex diagnosis

An infant or child must be diagnosed as having abusive head trauma by a team of pediatric specialists. Usually, a concerned parent or caregiver who may or may not know an infant has been injured becomes concerned that the child is not behaving normally. The child may have symptoms ranging from persistent vomiting to seizures or even seem unconscious.

The medical team begins addressing the child’s condition through blood testing and X-rays. Often a CT scan is performed in order to determine if there is a brain injury or some other abnormality. Bleeding around the brain is an indicator of trauma. However, other conditions can also cause this type of bleeding, including bleeding disorders, vitamin deficiency or genetic problems.

Carefully assessing a child for all of these possibilities may lead to discovery of other areas of trauma, such as broken bones and bruises. A child abuse physician is often called in to assist with the evaluation when trauma becomes a leading diagnosis. That trauma could be accidental, or it could be a sign that someone has abused or hurt an infant.

There are other medical conditions and even accidental injuries to a child that may resemble abusive head trauma. Experienced clinicians will evaluate a child carefully for these well-described conditions. Controversy about many of these conditions may exist in the courtroom, but in the medical setting it is often clear which conditions are present and when injuries are caused by trauma versus other medical conditions.

All 50 states and territories of the U.S. require that a report is made to child protective services agencies, with law enforcement often being involved when someone suspects or knows that a baby has been shaken.

Investigators and doctors work together along with parents and caregivers to try to determine what led to the infant or child’s condition. Bruising, fractures and retinal hemorrhages may support a diagnosis of child abuse, specifically shaken baby syndrome.

During an investigation, a rare accidental cause may be determined. The purpose is to make sure infants and children are not being harmed or that a medical condition is uncovered that can be treated.

As a pediatrician working in a children’s hospital and trauma center, it will never get easier for me to see infants and children with abusive injuries as well as other head traumas. The U.S. has come a long way in ensuring the safety of children through the use of car seats and many safety devices.

Education can help

Crying in infancy is a common trigger in cases where shaking occurs. Other risk factors include isolation, poverty, domestic violence and substance use. During severe economic downturns, the rate of shaken baby incidents rises, since research shows that social stressors often contribute.

Although anyone can injure a baby in a moment of frustration, most prevention research has focused specifically on helping parents understand why infants cry or become fussy. Recognizing your infant’s needs and addressing those needs is an important piece of learning how to parent. Studies have shown that focused education for new parents in maternity wards by nurses is effective.

If you or someone you know is concerned that a child or infant is being harmed in any way, each state has a process for reporting these concerns to appropriate authorities. Reporting can help prevent further harm to an infant and provide assistance to families.

The National Center on Shaken Baby Syndrome, the American Academy of Pediatrics and the Centers for Disease Control and Prevention offer some helpful resources.

Lori Frasier, Professor of Pediatrics, Penn State

This article is republished from The Conversation under a Creative Commons license. Read the original article.