Late-stage RSV vaccine trials show ‘exciting promise,’ some scientists say

By Jen Christensen, CNN

A Pfizer vaccine to protect older adults and infants from respiratory syncytial virus (RSV) infection has shown what some scientists are calling “exciting” promise in late-stage trials.

In one company-funded trial in adults 60 and older, the results of which were published Wednesday in the New England Journal of Medicine, the vaccine prevented RSV-associated lower respiratory tract illness — which includes acute bronchitis and pneumonia — and prevented RSV-associated acute respiratory illness, with no apparent safety concerns.

In another company trial, whose interim results were also published in the journal on Wednesday, the RSV vaccine was given during late-stage pregnancy and was found to be effective against severe RSV-associated lower respiratory tract illness such as pneumonia and bronchiolitis, or inflammation of the small airway passages entering the lungs, in infants. There were no safety concerns identified.

Pfizer is seeking the US Food and Drug Administration’s approval for its RSV vaccine for older adults.

In a separate request, Pfizer has asked the FDA to approve its RSV vaccine with pregnant people to protect infants. The company says it expects that decision by August.

The FDA is also considering a monoclonal antibody treatment that’s designed to protect children up to 2 years old.

In March, vaccine advisers to the FDA voted in favor of approving RSV vaccine candidates from Pfizer and GlaxoSmithKline (GSK) for adults over 60.

The vaccines could become the world’s first if the FDA commissioner agrees with the advisory committee.

Why an RSV vaccine is needed

RSV is ubiquitous. The US Centers for Disease Control and Prevention says most kids will catch this highly contagious respiratory virus at some point before they turn 2.

Although RSV is a mild infection for most, for some groups like infants and the elderly, it can be serious enough to cause hospitalization or death.

“When I started my residency 30 years ago, RSV season was literally a horrifying event for us in pediatrics,” said Dr. Claudia Hoyen, director of pediatric infection control at UH Rainbow Babies and Children’s Hospital in Cleveland, who was not involved in the new studies.

Providers would work hard to save babies who were in the NICU for other reasons, she said, but when RSV season would come around, they’d lose many of those babies.

“It was just … heartbreaking,” Hoyen said.

The introduction of monoclonal antibodies for these most vulnerable infants made RSV survivable for many, but still some are lost to the virus.

Globally, about 64 million people get sick with RSV each year, and 160,000 die, according to the National Institute of Allergy and Infectious Disease.

During last year’s especially bad RSV season, some children’s hospitals had to set up tents in their parking lots to deal with the overflow of patients. But even in a typical RSV season, hospitals stay busy.

In a single year, there are about 34 million episodes of RSV-associated lower respiratory tract infections in children under the age of 5, and about 10% need to go to the hospital for treatment, studies show. In fact, the virus is the No. 1 reason infants in the US have to go to the hospital.

Tens of thousands of older adults are also hospitalized every year, according to the National Foundation for Infectious Diseases.

RSV is costly, too. Every year, the US spends more than $709.6 million on hospitalization for infants with RSV alone, studies show.

An inauspicious start

There is no specific treatment for RSV. Some babies who are more vulnerable to severe disease can get a monoclonal antibody, but it’s been difficult to administer and requires parents to come into the clinic at least once a month during RSV season. A vaccine would be incredibly helpful, doctors say, but trials have been stalled until recently.

In the 1960s, a disastrous RSV vaccine effort using an inactivated virus saw the hospitalizations of 80% of vaccinated children who later caught RSV. Only 5% of the young participants who got a placebo were hospitalized.

Further trials were put on hold for years as scientists worked to determine what went wrong. In the meantime, the US government created more guardrails to make clinical trials safer going forward.

A decade agom a research team at the National Institutes of Health figured out a key mechanism of the virus. Scientists could build on that knowledge to create safe vaccines that would recognize the virus when it invaded the body and trigger the body to develop strong protection against it.

The RSV vaccine race

Until recently, four companies had RSV vaccines for seniors in the final phases of trials.

Johnson & Johnson’s vaccine division, Janssen, was far along. But at the end of March, the company announced that it was abandoning its candidate.

J&J said the vaccine was lost in the company’s “broader effort to make strategic choices for its pipeline and research and development (R&D) investments to focus on medicines with the greatest potential benefit to patients.”

That leaves Bavarian Nordic as the other company focused on a vaccine for the elderly. Results from its trial are expected in the middle of this year.

The vaccines by the numbers

When the FDA’s independent vaccine advisers voted to recommend that the agency approve Pfizer and GSK’s vaccines for seniors, the companies showed promising data.

GSK’s RSV vaccine candidate for older adults was 82.6% effective in preventing lower respiratory tract disease, according to a company-funded study published in NEJM in February. The shot was 94.1% effective at preventing severe disease.

For Pfizer’s vaccine for people 60 and older, Wednesday’s studies showed 66.7% efficacy against RSV-associated lower respiratory tract illness with two or more signs or symptoms and 85.7% vaccine efficacy against RSV-associated lower respiratory tract illness with three or more signs or symptoms.

The study says there were not enough cases of severe RSV-associated lower respiratory tract illness, meaning hospitalization or a need for ventilation or extra oxygen, to derive that effectiveness.

One reason may be that the trials were conducted during the Covid-19 pandemic, when there weren’t as many RSV cases as usual, Dr. Ann Falsey said.

“Event rates were low. So, for that reason, they just could not say that it decreased hospitalization, but in my mind, anything that prevents ARI, respiratory infection and lower respiratory tract infection will clearly lead to less hospitalizations. This makes immense sense, but they didn’t prove it,” said Falsey, who was involved in the new research and cares for elderly RSV patients. She is a professor of medicine at the University of Rochester School of Medicine.

The Pfizer vaccine was considered safe, according to the study.

Among the 20,000 recipients in the trial, there was one case of Guillain-Barré syndrome, a rare disorder in which the body’s immune system attacks the nerves, a week after vaccination. Company documents show that the case was considered life-threatening, but there may have been a compounding factor, because the person had a heart attack the day before doctors noted the Guillain-Barre.

There was also a case of Miller-Fisher syndrome, another rare nerve disease that’s considered a variant of Guillain-Barré. The person developed the disease eight days after vaccination but recovered after about a month and a half.

During the independent FDA advisers’ discussion about the vaccine, Dr. Hana El Sahly, chair of the committee and a professor of virology at the Baylor College of Medicine, said that the two cases put the rate of the condition at about 1 in 9,000, which is much higher than what is seen in the general population.

A person in the GSK trial also developed Guillain-Barré nine days after getting the vaccine and spent six months in rehabilitation. The FDA considers the case possibly vaccine-related.

If the vaccines are approved, doctors say, it will be important to monitor their safety.

RSV vaccine for young children

The interim results of Pfizer’s vaccine for infants show that the candidate didn’t meet the company’s criteria, again most likely because the trial took place during the pandemic, when RSV cases were lower. But research is ongoing.

An editorial published alongside the study Wednesday from Dr. Ruth Karron says “it is notable that the efficacy against severe RSV-associated lower respiratory tract illness was 81.8% within 90 days after birth and 69.4% within 180 days after birth.” In other words, it didn’t necessarily prevent infections, but it kept them from getting worse.

Karron — a professor in the Department of International Health at Johns Hopkins Bloomberg School of Public Health and director of the Center for Immunization Research and of the Johns Hopkins Vaccine Initiative, who was not involved in the new research — wondered in the editorial whether this age of RSV vaccine development could be the “beginning of the end” of huge RSV outbreaks.

Another study published Wednesday in NEJM focused on nirsevimab, a monoclonal antibody to prevent RSV made by AstraZeneca and Sanofi, which has been approved by the European Commission and the UK to prevent infants from getting sick with RSV.

The companies have asked the FDA for approval to use the treatment to protect children up to age 2.

This study found that through 150 days after injection, efficacy against hospitalization for RSV-associated lower respiratory tract infection was 76.8%, and efficacy against very severe medically attended RSV-associated lower respiratory tract infection was 78.6%.

Ultimately, in babies carried to term and in late-preterm infants, a single dose provided protection against hospitalization with RSV.

Hoyen thinks it will take a monoclonal antibody treatment as well as a vaccine to protect infants. Many pregnant women don’t get vaccinated; at most, only 57% to 61% of pregnant people get shots to protect against the flu and tetanus-diphtheria-acellular pertussis, according to a 2020 study from the CDC.

“We try, but overall, we do not do a great job of vaccinating mothers when they’re pregnant,” Hoyen said.

Now, it will be up to the government to decide how these vaccines and treatment should be used. Scientists will also be watching to see how long the vaccine provides protection in the next RSV season.

Even with all those caveats, health care providers who treat people with RSV say, it’s incredible news.

“I’m just unbelievably happy with all of these results. You know, for somebody who’s been laboring in the field for more than 30 years, it’s immensely satisfying to see both a vaccine for babies who need it and a vaccine for older adults. It’s terrific,” Falsey said.

Dr. William Schaffner, a professor in the Division of Infectious Diseases at Vanderbilt University Medical Center and medical director of the National Foundation for Infectious Diseases, said vaccines like these could be a huge help for public health.

“RSV is an enormous problem, particularly for children but also for adults. RSV could produce as much illness as does influenza at least in some years,” said Schaffner, who was not involved in the new research. “These are exciting potential advances. We will see them develop as several products come to maturation and come before the Food and Drug Administration for licensure this year or next year. It’s going to be an exciting time.”

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This story has been updated to correct that Dr. Falsey did work on the RSV study for adults.