Day: August 16, 2022

NASA’s gigantic Space Launch System moon rocket, topped with an uncrewed astronaut capsule, is set to begin an hourslong crawl to its launchpad Tuesday night ahead of the behemoth’s debut test flight later this month. 

The 98-meter-tall rocket is scheduled to embark on its first mission to space — without any humans — on August 29. It will be a crucial, long-delayed demonstration trip to the moon in NASA’s Artemis program, the United States’ multibillion-dollar effort to return humans to the lunar surface as practice for future missions to Mars. 

The Space Launch System, whose development in the past decade has been led by Boeing, is scheduled to emerge from its assembly building at NASA’s Kennedy Space Center in Florida around 9 p.m. EDT on Tuesday (0100 GMT on Wednesday) and begin the 6-km-long trek to its launchpad. Moving less than 1.6 km per hour, the rollout takes roughly 11 hours. 

Sitting atop the rocket is NASA’s Orion astronaut capsule, a pod built by Lockheed Martin Corp LMT.N. It is designed to separate from the rocket in space, ferry humans toward the moon’s vicinity and rendezvous with a separate spacecraft that will take astronauts down to the lunar surface. 

But for the August 29 mission, called Artemis 1, the Orion capsule will launch atop the Space Launch System without any humans and orbit around the moon before returning to Earth for an ocean splashdown 42 days later. 

If bad launch weather or a minor technical issue triggers a delay from August 29, the National Aeronautics and Space Administration has backup launch dates on September 2 and September 5. 

 
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New York health officials announced in July that an unvaccinated adult man from Rockland County had been diagnosed with polio—the first case of the life-threatening disease in the United States since 2013. The virus that causes polio was later detected in New York City wastewater, and city and state health officials now say the virus is probably circulating in the city.

The virus identified in New York is a vaccine-derived poliovirus. Wild polioviruses were eliminated from most of the world and now circulate only in Afghanistan and Pakistan.

But vaccine-derived viruses, which emerge when the weakened viruses in the oral polio vaccine mutate and spread in unvaccinated populations, still occasionally cause outbreaks.

VOA spoke with three polio experts about vaccine-derived polioviruses and the oral polio vaccine. Here’s what you need to know.

What are vaccine-derived polioviruses?

Vaccine-derived polioviruses are related to the active viruses in the oral polio vaccine (OPV).

OPV works by infecting cells in the gut with weakened polioviruses, allowing the body to safely develop immunity to polio without the risk of paralysis posed by the real disease.

“[The weakened viruses] would still infect you. They would still replicate in your gut. You will develop a lifelong immunity, but you will not get paralyzed,” said virologist Konstantin Chumakov, a Global Virus Network Center of Excellence director and an adjunct professor at The George Washington University.

“But the [vaccine-derived] virus will still be able to transmit [from person to person],” Chumakov added. “It was considered a big advantage of the vaccine, because basically, you can immunize several kids with one dose.”

This transmission becomes problematic in communities with low vaccination rates. If the virus can spread for a long time, it has many chances to mutate and revert to a dangerous paralytic form.

Why is the oral polio vaccine (OPV) used?

Although OPV is linked to vaccine-derived polioviruses, it also has a number of advantages over the inactivated polio vaccine (IPV) — the injected vaccine — which is still used in most of the world.

People who receive OPV cannot be “silent spreaders.” After developing an immune response to the vaccine, they are immune to polio for life. Polioviruses cannot replicate in their gut and infect others.

In contrast, IPV protects against paralysis, but does not prevent the virus from replicating in the gut. People who receive IPV can spread polio, even though they won’t get sick from it.

“In populations where you want to stop the spread, that ‘gut immunity’ that OPV confers is essential,” said Captain Derek Ehrhardt, a polio incident manager at the Centers for Disease Control and Prevention (CDC). “If you have just IPV, it’s possible that the child will be protected, but they could still spread [paralytic polio] to their neighbor, their brother, their sister, whomever.”

This made OPV instrumental in the eradication of wild polio from most of the world, including in countries such as the United States that now use IPV exclusively.

OPV also has other advantages.

“We work with oral polio vaccine because it is low cost,” said Richter Razafindratsimandresy, head of the National Reference Laboratory for Poliomyelitis at the Institut Pasteur de Madagascar. “And it is easy to administer, because it is oral — they don’t need to inject the children, and it is not a problem for the parents to accept.”

If OPV prevents silent spread, why are the U.S. and other nations using only IPV?

After the United States and other wealthy countries eliminated wild polio, they stopped using OPV because it carries the risk of creating vaccine-derived polioviruses in undervaccinated communities, and because it has a slight risk of causing paralysis. This happens between roughly two and four times per million births, according to the Global Polio Eradication Initiative (GPEI). Because there are so few cases in the U.S., thanks to the very successful campaigns with OPV, that risk is now seen as unacceptable.

The U.S. and other wealthy countries have robust health care systems and can effectively acquire the more expensive IPV and get it into every arm. So, using IPV means the well-vaccinated populations in these countries are well-protected from paralysis from polio, despite being less protected against catching and spreading polioviruses.

How do vaccine-derived poliovirus cause outbreaks?

Countries with weak vaccination systems are more likely to experience outbreaks of vaccine-derived poliovirus. That’s happened several times in Madagascar, Razafindratsimandresy said.

“[The virus] is not from another country. Because in Madagascar, we have … immunization coverage [that] is very, very low,” he said.

Imported vaccine-derived polioviruses can also cause outbreaks in countries with high vaccination rates, especially if IPV is used instead of OPV.

“Basically, it can transmit from person to person to person without causing any symptoms, because everybody is protected from paralysis,” said Chumakov. “But at some point, the virus can hit an unvaccinated person or a person with immune deficiency, and then it can paralyze this person. And this is exactly what happened in New York.”

Is OPV safe?

“Our vaccines are safe and effective,” said Ehrhardt. “We need to vaccinate our under- and unimmunized children to stop the ongoing spread of these viruses.”

Chumakov said that developing better versions of OPV could reduce risks while also keeping the gut immunity provided by OPV, which he said is important for preventing silent spread. He was previously involved in a GPEI effort to develop a safer oral vaccine for Type 2 polioviruses. Clinical trial data suggest the novel OPV is less likely to revert to a dangerous form.

While the future may bring improved vaccines, vaccinating as many children as possible with existing OPV remains a priority in much of the world.

According to the CDC, global polio vaccination coverage sunk to 81% in 2021, the lowest in a decade. This was largely due to the COVID-19 pandemic, but not all countries have enough resources for vaccination campaigns even in normal times.

Razafindratsimandresy said that even though Madagascar aims to vaccinate all children with OPV, the country doesn’t have enough personnel and often runs out of vaccine.

“These immunity gaps must be closed for us to stop these diseases,” Ehrhardt said. “If you have polio anywhere, then children everywhere are still at risk.”

 
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The widely used tuberculosis vaccine also fends off a slew of unrelated infectious diseases, and its immune boost can protect newborns for more than a year, researchers in Australia have found.

The bacillus calmette-guérin (BCG) vaccine for tuberculosis causes front-line immune cells to make long-lasting biological “marks” on their DNA, changing how they read genetic instructions for fighting off viruses, the researchers say.

“The DNA is like the manual for the cell. It tells you what it can and can’t do,” study author and molecular immunologist Boris Novakovic of the University of Melbourne told VOA. “You might have a sentence that says, ‘If you see a virus, turn the following genes on.’ And what we’ve done with the BCG vaccine [is] sort of [change] that full stop at the end of that sentence to an exclamation mark.”

The findings were published in the Science Advances journal.

“What is new here is the durability, the long-lasting imprinting effects of BCG vaccine at birth in these Australian babies, and also [that] they can show [in detail] how that takes place,” vaccine epidemiologist Christine Stabell Benn, of the University of Southern Denmark, said in an interview with VOA. She was not involved in the study.

Developed more than a century ago, the BCG vaccine contains live, weakened bacteria. It is one of the oldest vaccines still used and is the most frequently administered vaccine in the world.

Decades ago, Benn and her colleagues noticed that children in Guinea-Bissau who received the tuberculosis shot were less likely to die from other, unrelated diseases. They later confirmed this in a randomized trial, showing that low-birthweight babies who got BCG at birth were about a third less likely to die in their first month of life than those who got BCG later on the normal schedule. Later trials in Guinea-Bissau and Uganda corroborated these findings.

Today, this “non-specific effect” of BCG vaccination has been observed in babies, healthy adults and elderly people. The vaccine’s immune boost is used to treat bladder cancer. Clinical trials are ongoing to see if it could help protect against COVID-19.

There is growing evidence that BCG trains the innate immune system — the non-specific, fast-acting response that activates to fight a wide range of threats.

But it wasn’t until recently that scientists started to figure out how this “trained immunity” that the BCG vaccine generates actually works.

Previous studies found marks of trained immunity a month to three months after BCG vaccination in adults. But the vaccine is typically administered to young babies, and scientists had not tested whether training could last for a long time.

Novakovic and his colleagues compared the immune cells of 63 newborns who received the BCG vaccine right after birth to those of 67 babies who didn’t get the vaccine. They found that exposure to BCG left marks on virus-fighting regions of the genome that tell cells to activate specific genes more or less often. Immune cells passed down these marks, generation to generation, as they divided to make new cells. The marks of trained immunity persisted for more than a year.

In lab tests using cultured human immune cells, the scientists were able to piece together the cellular machinery involved in making these marks more precisely than before.

“We were able to look at all these different levels to see, in a really comprehensive way, what happens to these cells when they directly get exposed to BCG,” said Novakovic.

In the future, Novakovic — who also works at the Murdoch Children’s Research Institute — said he’d like to see if the study’s findings hold in different populations — especially in places where infectious disease is more common than in Australia. And in the long term, he thinks scientists should design vaccines that specifically target the immune-boosting pathways BCG incidentally activates.

“The BCG vaccine is great — it’s safe, and it works. But it’s a bit of a dirty method because we don’t really know what it does. We just know it works,” he said. “Imagine you can just make a purely trained-immunity vaccine.”

Benn said future studies should consider factors such as sex and mother’s vaccination status, which epidemiologists have noticed can affect the immune boost from BCG. For instance, boys seem to benefit from the vaccine’s extra protection more than girls during the first weeks of life, she said.

But beyond more research, Benn hopes the new study will give public health officials more confidence in off-target immunity from BCG, a vaccine she says should be recommended as protection against death from infectious disease — not just as a tuberculosis vaccine.

“I feel that we’re sitting on our hands,” she said, “waiting for biological mechanisms while children could be saved.”
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