David Higgins, University of Colorado Anschutz Medical Campus

The committee advising the Centers for Disease Control and Prevention on vaccine policy voted on Dec. 5, 2025, to stop recommending that all newborns be routinely vaccinated against the hepatitis B virus – undoing a 34-year prevention strategy that has nearly eliminated early childhood hepatitis B infections in the United States.

Before the U.S. began vaccinating all infants at birth with the hepatitis B vaccine in 1991, around 18,000 children every year contracted the virus before their 10th birthday – about half of them at birth. About 90% of that subset developed a chronic infection.

In the U.S., 1 in 4 children chronically infected with hepatitis B will die prematurely from cirrhosis or liver cancer.

Today, fewer than 1,000 American children or adolescents contract the virus every year – a 95% drop. Fewer than 20 babies each year are reported infected at birth.

I am a pediatrician and preventive medicine specialist who studies vaccine delivery and policy. Vaccinating babies for hepatitis B at birth remains one of the clearest, most evidence-based ways to keep American children free of this lifelong, deadly infection.

What spurred the change?

In September 2025, the Advisory Committee on Immunization Practices, or ACIP, an independent panel of experts that advises the CDC, debated changing the recommendation for a dose of the hepatitis B vaccine at birth, but ultimately delayed the vote.

This committee regularly reviews vaccine guidance. However, since Secretary of Health and Human Services Robert F. Kennedy Jr. disbanded the entire committee and handpicked new members, its activity has drastically departed from business as usual. The committee has long-standing procedures for evaluating evidence on the risks and benefits of vaccines, but these procedures were not followed in the September meeting and were not followed for this most recent decision.

The committee’s new recommendation keeps the hepatitis B vaccine at birth for infants whose mothers test positive for the virus. But the committee now advises that infants whose mothers test negative should consult with their health care provider. Parents and health care providers are instructed to weigh vaccine benefits, vaccine risks and infection risks using “individual-based decision-making” or “shared clinical decision-making.”

On the surface, this sounds reasonable. But while parents have always been free to discuss benefits and risks with their health care providers to make a decision on what’s best for their child, this change is not based on any new evidence, and it introduces uncertainty into a recommendation that has long been clear.

As a doctor, I am already seeing this uncertainty play out in the clinic. I recently had new parents ask to postpone the hepatitis B vaccine until adolescence because they believed federal health leaders had evidence that people only become infected through sexual activity or contaminated needle use.

After a brief conversation, they came to understand that this was inaccurate — children can be infected not only at birth but also through routine household or child care exposures, including shared toothbrushes or even a bite that breaks the skin. In the end, they chose to vaccinate, but this experience highlights how easily well-intentioned parents can be misled when guidance is not clear and consistent.

Why the CDC adopted universal hepatitis B shots

Hepatitis B is a virus that infects liver cells, causing inflammation and damage. It is spread through blood and bodily fluids and is easily transmitted from mother to baby during delivery.

The hepatitis B vaccine has been available since the early 1980s. Before 1991, public health guidance recommended giving newborns the hepatitis B vaccine only if they were at high risk of being infected – for example, if they were born to a mother infected with hepatitis B.

That targeted plan failed. Tens of thousands of infants were still infected each year.

Some newborns were exposed when their mothers weren’t screened; others were exposed after their mothers were infected late in pregnancy, after their initial screening. And like any lab test, the screening can have false negative results, be misinterpreted or not be communicated properly to the baby’s care team.

Recognizing these gaps, in 1991 the CDC recommended hepatitis B vaccination for every child starting at birth, regardless of maternal risk.

The U.S. adopted a policy of vaccinating all babies from birth because the number of people with hepatitis B infections was, and remains, relatively high, and because many mothers do not receive prenatal care, so their infections go undetected.

Meanwhile, in some European countries, like Denmark, only babies with certain risk factors receive the vaccine at birth. That’s because in those countries, hepatitis B infections are much less prevalent and pregnant mothers are more widely tested due to universal health care. Due to these differences, that approach is not effective in the United States. In fact, most World Health Organization member countries do recommend a universal birth dose.

Vaccinating at birth

The greatest danger for infants contracting hepatitis B is at birth, when contact with a mother’s blood can transmit the virus. Without preventive treatment or vaccination, 70% to 90% of infants born to infected mothers will become infected themselves, and 90% of those infections will become chronic. The infection in these children silently damages their liver, potentially leading to liver cancer and death.

About 80% of parents choose to vaccinate their babies at birth. If parents choose to delay vaccination due to this new recommendation, it will leave babies unprotected during this most vulnerable window, when infection is most likely to lead to chronic infection and silently damage the liver.

A research article published on Dec. 3, 2025, estimates that if only infants born to mothers infected with hepatitis B received the vaccine, an additional 476 perinatal hepatitis B infections would occur each year.

The hepatitis B vaccines used in the U.S. have an outstanding safety record. The only confirmed risk is an allergic reaction called anaphylaxis that occurs in roughly 1 in 600,000 doses, and no child has died from such a reaction. Extensive studies show no link to other serious conditions.

How children get exposed to hepatitis B

Infants and children continue to be vulnerable to hepatitis B long after birth.

Children can become infected through household contacts or in child care settings by exposures as ordinary as shared toothbrushes or a bite that breaks the skin. Because hepatitis B can survive for a week on household surfaces, and many carriers are unaware they are infected, even babies and toddlers of uninfected mothers remained at risk.

Full protection against hepatitis B requires a three-dose vaccine series, given at specific intervals in infancy. Anything short of the full series leaves children vulnerable for life.

In addition to changing the birth dose recommendation, the committee is now advising parents to consult with their health care provider about checking children’s antibody levels after one or two doses of the vaccine to determine whether additional doses are needed. While such testing is sometimes recommended for people in high-risk groups after they get all three doses to confirm their immune system properly responded to the vaccine, it is not a substitute for completing the series.

The recommendation for all babies to receive the vaccine at birth and for infants to complete the full vaccine series is designed to protect every child, including those who slip through gaps in maternal screening or encounter the virus in everyday life. A reversion to the less effective risk-based approach threatens to erode this critical safety net.

Portions of this article originally appeared in a previous article published on Sept. 9, 2025.

David Higgins, Assistant Professor of Pediatrics, University of Colorado Anschutz Medical Campus

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

Ivis García, Texas A&M University

Picture this: You’re looking to buy a place to live, and you have two options.

Option A is a beautiful home in California near good schools and job opportunities. But it goes for nearly a million dollars – the median California home sells for US$906,500 – and you’d be paying a mortgage that’s risen 82% since January 2020.

Option B is a similar home in Texas, where the median home costs less than half as much: just $353,700. The catch? Option B sits in an area with significant hurricane and flood risk.

As a professor of urban planning, I know this isn’t just a hypothetical scenario. It’s the impossible choice millions of Americans face every day as the U.S. housing crisis collides with climate change. And we’re not handling it well.

The numbers tell the story

The migration patterns are stark. Take California, which lost 239,575 residents in 2024 – the largest out-migration of any state. High housing costs are a primary driver: The median home price in California is more than double the national median.

Where are these displaced residents going? Many are heading to southern and western states like Florida and Texas. Texas, which is the top destination for former California residents, saw a net gain of 85,267 people in 2024, much of it from domestic migration. These newcomers are drawn primarily by more affordable housing markets.

This isn’t simply people chasing lower taxes. It’s a housing affordability crisis in motion. The annual household income needed to qualify for a mortgage on a mid-tier California home was about $237,000 in June 2025, a recent analysis found – over twice the state’s median household income.

Over 21 million renter households nationwide spent more than 30% of their income on housing costs in 2023, according to the U.S. Census Bureau. For them and others struggling to get by, the financial math is simple, even if the risk calculation isn’t.

I find this troubling. In essence, the U.S. is creating a system where your income determines your exposure to climate disasters. When housing becomes unaffordable in safer areas, the only available and affordable property is often in riskier locations – low-lying areas at flood risk in Houston and coastal Texas, or higher-wildfire-risk areas as California cities expand into fire-prone foothills and canyons.

Climate risk becomes part of the equation

The destinations drawing newcomers aren’t exactly safe havens. Research shows that America’s high-fire-risk counties saw 63,365 more people move in than out in 2023, much of that flowing to Texas. Meanwhile, my own research and other studies of post-disaster recovery have shown how the most vulnerable communities – low-income residents, people of color, renters – face the greatest barriers to rebuilding after disasters strike.

Consider the insurance crisis brewing in these destination states. Dozens of insurers in Florida, Louisiana, Texas and beyond have collapsed in recent years, unable to sustain the mounting claims from increasingly frequent and severe disasters like wildfires and hurricanes. Economists Benjamin Keys and Philip Mulder, who study climate change impacts on real estate, describe the insurance markets in some high-risk areas as “broken”. Between 2018 and 2023, insurers canceled nearly 2 million homeowner policies nationwide – four times the historically typical rate.

Yet people keep moving into risky areas. For example, recent research shows that people have been moving toward areas most at risk of wildfires, even holding wealth and other factors constant. The wild beauty of fire-prone areas may be part of the attraction, but so is housing availability and cost.

The policy failures behind the false choice

In my view, this isn’t really about individual choice – it’s about policy failure. The state of California aims to build 2.5 million new homes by 2030, which would require adding more than 350,000 units annually. Yet in 2024, the state only added about 100,000 – falling dramatically short of what’s needed. When local governments restrict housing development through exclusionary zoning, they’re effectively pricing out working families and pushing them toward risk.

My research on disaster recovery has consistently shown how housing policies intersect with climate vulnerability. Communities with limited housing options before disasters become even more constrained afterward. People can’t “choose” resilience if resilient places won’t let them build affordable housing.

The federal government started recognizing this connection – to an extent. For example, in 2023, the Federal Emergency Management Agency encouraged communities to consider “social vulnerability” in disaster planning, in addition to things like geographic risk. Social vulnerability refers to socioeconomic factors like poverty, lack of transportation or language barriers that make it harder for communities to deal with disasters.

However, the agency more recently stepped back from that move – just as the 2025 hurricane season began.

In my view, when a society forces people to choose between paying for housing and staying safe, that society has failed. Housing should be a right, not a risk calculation.

But until decision-makers address the underlying policies that create housing scarcity in safe areas and fail to protect people in vulnerable ones, climate change will continue to reshape who gets to live where – and who gets left behind when the next disaster strikes.

Ivis García, Associate Professor of Landscape Architecture and Urban Planning, Texas A&M University

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

Mojtaba Akhavan-Tafti, University of Michigan

The rapid expansion of artificial intelligence and cloud services has led to a massive demand for computing power. The surge has strained data infrastructure, which requires lots of electricity to operate. A single, medium-sized data center here on Earth can consume enough electricity to power about 16,500 homes, with even larger facilities using as much as a small city.

Over the past few years, tech leaders have increasingly advocated for space-based AI infrastructure as a way to address the power requirements of data centers.

In space, sunshine – which solar panels can convert into electricity – is abundant and reliable. On Nov. 4, 2025, Google unveiled Project Suncatcher, a bold proposal to launch an 81-satellite constellation into low Earth orbit. It plans to use the constellation to harvest sunlight to power the next generation of AI data centers in space. So, instead of beaming power back to Earth, the constellation would beam data back to Earth.

For example, if you asked a chatbot how to bake sourdough bread, instead of firing up a data center in Virginia to craft a response, your query would be beamed up to the constellation in space, processed by chips running purely on solar energy, and the recipe sent back down to your device. Doing so would mean leaving the substantial heat generated behind in the cold vacuum of space.

As a technology entrepreneur, I applaud Google’s ambitious plan. But as a space scientist, I predict that the company will soon have to reckon with a growing problem: space debris.

The mathematics of disaster

Space debris – the collection of defunct human-made objects in Earth’s orbit – is already affecting space agencies, companies and astronauts. This debris includes large pieces, such as spent rocket stages and dead satellites, as well as tiny flecks of paint and other fragments from discontinued satellites.

Space debris travels at hypersonic speeds of approximately 17,500 miles per hour (28,000 km/h) in low Earth orbit. At this speed, colliding with a piece of debris the size of a blueberry would feel like being hit by a falling anvil.

Satellite breakups and anti-satellite tests have created an alarming amount of debris, a crisis now exacerbated by the rapid expansion of commercial constellations such as SpaceX’s Starlink. The Starlink network has more than 7,500 satellites, which provide global high-speed internet.

The U.S. Space Force actively tracks over 40,000 objects larger than a softball using ground-based radar and optical telescopes. However, this number represents less than 1% of the lethal objects in orbit. The majority are too small for these telescopes to reliably identify and track.

In November 2025, three Chinese astronauts aboard the Tiangong space station were forced to delay their return to Earth because their capsule had been struck by a piece of space debris. Back in 2018, a similar incident on the International Space Station challenged relations between the United States and Russia, as Russian media speculated that a NASA astronaut may have deliberately sabotaged the station.

The orbital shell Google’s project targets – a Sun-synchronous orbit approximately 400 miles (650 kilometers) above Earth – is a prime location for uninterrupted solar energy. At this orbit, the spacecraft’s solar arrays will always be in direct sunshine, where they can generate electricity to power the onboard AI payload. But for this reason, Sun-synchronous orbit is also the single most congested highway in low Earth orbit, and objects in this orbit are the most likely to collide with other satellites or debris.

As new objects arrive and existing objects break apart, low Earth orbit could approach Kessler syndrome. In this theory, once the number of objects in low Earth orbit exceeds a critical threshold, collisions between objects generate a cascade of new debris. Eventually, this cascade of collisions could render certain orbits entirely unusable.

Implications for Project Suncatcher

Project Suncatcher proposes a cluster of satellites carrying large solar panels. They would fly with a radius of just one kilometer, each node spaced less than 200 meters apart. To put that in perspective, imagine a racetrack roughly the size of the Daytona International Speedway, where 81 cars race at 17,500 miles per hour – while separated by gaps about the distance you need to safely brake on the highway.

This ultradense formation is necessary for the satellites to transmit data to each other. The constellation splits complex AI workloads across all its 81 units, enabling them to “think” and process data simultaneously as a single, massive, distributed brain. Google is partnering with a space company to launch two prototype satellites by early 2027 to validate the hardware.

But in the vacuum of space, flying in formation is a constant battle against physics. While the atmosphere in low Earth orbit is incredibly thin, it is not empty. Sparse air particles create orbital drag on satellites – this force pushes against the spacecraft, slowing it down and forcing it to drop in altitude. Satellites with large surface areas have more issues with drag, as they can act like a sail catching the wind.

To add to this complexity, streams of particles and magnetic fields from the Sun – known as space weather – can cause the density of air particles in low Earth orbit to fluctuate in unpredictable ways. These fluctuations directly affect orbital drag.

When satellites are spaced less than 200 meters apart, the margin for error evaporates. A single impact could not only destroy one satellite but send it blasting into its neighbors, triggering a cascade that could wipe out the entire cluster and randomly scatter millions of new pieces of debris into an orbit that is already a minefield.

The importance of active avoidance

To prevent crashes and cascades, satellite companies could adopt a leave no trace standard, which means designing satellites that do not fragment, release debris or endanger their neighbors, and that can be safely removed from orbit. For a constellation as dense and intricate as Suncatcher, meeting this standard might require equipping the satellites with “reflexes” that autonomously detect and dance through a debris field. Suncatcher’s current design doesn’t include these active avoidance capabilities.

In the first six months of 2025 alone, SpaceX’s Starlink constellation performed a staggering 144,404 collision-avoidance maneuvers to dodge debris and other spacecraft. Similarly, Suncatcher would likely encounter debris larger than a grain of sand every five seconds.

Today’s object-tracking infrastructure is generally limited to debris larger than a softball, leaving millions of smaller debris pieces effectively invisible to satellite operators. Future constellations will need an onboard detection system that can actively spot these smaller threats and maneuver the satellite autonomously in real time.

Equipping Suncatcher with active collision avoidance capabilities would be an engineering feat. Because of the tight spacing, the constellation would need to respond as a single entity. Satellites would need to reposition in concert, similar to a synchronized flock of birds. Each satellite would need to react to the slightest shift of its neighbor.

Paying rent for the orbit

Technological solutions, however, can go only so far. In September 2022, the Federal Communications Commission created a rule requiring satellite operators to remove their spacecraft from orbit within five years of the mission’s completion. This typically involves a controlled de-orbit maneuver. Operators must now reserve enough fuel to fire the thrusters at the end of the mission to lower the satellite’s altitude, until atmospheric drag takes over and the spacecraft burns up in the atmosphere.

However, the rule does not address the debris already in space, nor any future debris, from accidents or mishaps. To tackle these issues, some policymakers have proposed a use-tax for space debris removal.

A use-tax or orbital-use fee would charge satellite operators a levy based on the orbital stress their constellation imposes, much like larger or heavier vehicles paying greater fees to use public roads. These funds would finance active debris removal missions, which capture and remove the most dangerous pieces of junk.

Avoiding collisions is a temporary technical fix, not a long-term solution to the space debris problem. As some companies look to space as a new home for data centers, and others continue to send satellite constellations into orbit, new policies and active debris removal programs can help keep low Earth orbit open for business.

Mojtaba Akhavan-Tafti, Associate Research Scientist, University of Michigan

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