The European Centre for Disease Prevention and Control (ECDC) has called for specialists to participate in a scientific expert panel that will create guidance on new vaccines to protect adults against respiratory syncytial virus (RSV).

RSV is an RNA virus that has long been recognized as the most common cause of pediatric acute lower respiratory tract disease, hospitalizing around 250,000 children younger than 5 years of age annually in Europe. RSV also leads to around 160,000 hospitalizations in older adults. “It causes serious illness in older adults,” Edoardo Colzani, MD, MPH, ECDC’s head of respiratory viruses, told Medscape News Europe. “Because of this substantial disease burden, [older adults] are considered a key target group for vaccination.”

The formation of the panel comes as European countries decide how to integrate new adult RSV vaccines into their vaccine schedules. The European Medicines Authority has authorized three vaccines since 2023. GSK’s Arexvy and Pfizer’s Abrysovo are protein vaccines, and Moderna’s mResvia is an RNA-based vaccine.

The 10-member scientific panel will ultimately aid with this integration and include experts in several fields, including epidemiology and surveillance; clinical and public health practice; virology, immunology, and vaccine science; biostatistics, modelling, and health economics; and health systems, behavioral sciences, and implementation. The plan is for the panel to meet, review available evidence, identify research gaps, analyze surveillance data, conduct systematic reviews, model outputs, and monitor priorities. It will then draft guidance on the optimal use of these vaccines and publish its results in June 2027.

Surveillance Provides Insights

The turn toward an adult vaccination strategy reflects a growing awareness of RSV’s impact on older patients. Such is the ubiquity of childhood RSV that countries have implemented or are about to implement RSV immunization strategies for newborns and pregnant women. But while it has been understood for decades that adults contract RSV, devasting outbreaks observed in old peoples’ nursing homes in the 1980s and the subsequent research have increased awareness of its dangers.

By 2023, ECDC had added RSV surveillance to reporting alongside COVID and influenza. It made sense to do so because these three viruses drive most seasonal respiratory illness and hospital pressure in Europe, said Colzani. “The decision was part of a broader strategy to modernize respiratory virus surveillance after the pandemic,” he said. “We recognized that RSV, influenza, and COVID-19 together account for a large share of winter respiratory disease, hospitalizations, and deaths in Europe.”

Joint surveillance helps track which virus is causing illness spikes and helps guide testing strategies and hospital resources. Monitoring RSV more systematically since 2023 has provided insights. Data suggest, for example, that the RSV season does not start and peak at the same time everywhere in Europe. Rather, it varies with geographic location. Nordic countries, Croatia, Denmark, and Germany often experience a major outbreak in winter and a minor one in the spring. In contrast, Spain and the UK see a stable annual epidemic. Indeed, in Spain, RSV seems to circulate between 2 and 8 weeks earlier than influenza viruses do.

Monitoring has contributed to the decision to vaccinate adults. “We now know adults aren’t necessarily getting RSV more than before, but ECDC surveillance now highlights that a substantial number of severe RSV cases occurs in older adults, which is why they are a priority group for vaccination,” added Colzani.

When to Boost?

But many questions surrounding the vaccines’ integration will need to be considered by the panel, which will act in an advisory capacity. It will consider everything from the RSV disease burden and seasonality to the timing of vaccination, as well as vaccine safety and efficacy.

Ongoing and emerging research into how RSV vaccines fare in the real world (as opposed to clinical trials) are informing these considerations, one of which is the appropriate patient population. The rates of hospitalization from RSV dramatically increase in adults aged 75 years or older, so countries may well consider vaccination programs aimed at all adults of a certain age, rather than at a few at-risk groups.

They also will have to consider patients younger than 75 years who have elevated risk for hospitalization. “It’s not just age, it’s age and underlying diseases, primarily underlying heart and lung disease,” said Ann R. Falsey, MD, professor of medicine at the University of Rochester School of Medicine in Rochester, New York. Falsey, who conducted many trials that established RSV’s effects, pointed to recent research from Surie and colleagues and Bajema and colleagues that suggests that the protection provided by vaccines declines over time, especially among immunocompromised patients.

“Everybody’s trying to figure out when you would want to boost, and there’s data that it’s not such an easy thing to do,” said Falsey. Scientists are finding that a new booster dose of vaccine may not necessarily provide a proportionate protective response. A so-called blunting effect has been observed, too. “If you don’t change one of the components of the vaccine, you don’t get as robust an immune response in that second year if you’re vaccinating with the same antigen,” she added. “There are multiple theories about why that happens.”

In its forthcoming analysis, the ECDC panel may name the identification of the most effective boosting strategy, a research gap, and a priority. But the organization has not provided details. “ECDC is not in a position to comment any further on identification of the knowledge gaps, as this would preempt the work that is yet to be done by the panel,” it said in a statement.

Colzani reported no relevant financial relationships. Falsey reported receiving consulting fees from ADMA Biologics, GSK, Sanofi Pasteur, and Merck.

Tatum Anderson is a global health and medical journalist. For over 20 years, she has placed articles in publications from the Bulletin of the World Health Organization to The Lancet, The BMJ, BBC News, and The Economist. She reported having no relevant financial relationships.