Small children across the US are falling ill with respiratory syncytial virus (RSV) at much higher rates than usual. RSV is a respiratory virus that a vast majority of babies are likely to get by their second birthday. But cases appear to be surging in the US and doctors say the same could happen in Europe this winter. 

What is RSV?

RSV is spread through respiratory secretions. Symptoms are similar to those of the common cold: a runny nose, low appetite, coughing, sneezing and fever.

Although most people recover after a couple of weeks, small children and older adults are more likely to experience serious bouts of it.

RSV makes headlines when it surges because in rare cases, infants can become very sick and require hospitalization. It can be "quite nasty" for some babies, especially those born prematurely because they have small airways and have yet to build up sufficient immunity to the virus, according to Christopher Green, a lecturer and consultant physician in infectious diseases at the University of Birmingham in the UK.

Of the millions of babies who are infected each year in high income countries, around 2-3% will end up in the hospital. About 5% of those will go to intensive care units. However, Green said, mortality rates in wealthy countries are "very, very low." 

The risk increases in countries where babies may not have access to proper care.

"It's estimated that around 99% of the deaths in young children due to RSV are in low and middle-income countries," said Christopher Chiu, a professor of infectious diseases at Imperial College London.

As people grow up and develop antibodies to the virus, cases of RSV become more like the common cold, said Green, although it can present a bigger risk for people with asthma, COPD or congestive heart failure.

People become more at risk of serious symptoms as they grow older and their immune systems weaken or if they develop heart or lung disease, making it harder for them to fight infections.

Why is RSV surging in the US? Will RSV surge in Europe?

The RSV season has been atypical over the past few years, during the COVID pandemic. In 2020, and in some places 2021, there was "virtually no RSV transmission going on," said Chiu. But this year's surge in the US is "almost definitely" because of the pandemic, he said.

"People were socially isolating and washing their hands and wearing masks, so the babies who were born during this period, in particular, haven't been exposed to very much RSV," said Chiu. "And this year, now that most places are relaxed, suddenly things are going back to normal and there's a big group of potential patients who haven't built up any immunity against RSV."

Richard Pebody, head of the High Threat Pathogen team at WHO/Europe, told DW that there was some low-level RSV circulation in Europe but that so far there hadn't been a big surge. However, said Pebody, now is the time when RSV starts to pick up.

"There is this potential that we might get co-circulation of RSV together with influenza and COVID," he said.

Chiu also said that he thinks RSV cases could surge in Europe over the course of the winter for the same reasons they are surging in the US.

Is there a vaccine for RSV?

There is currently no vaccine available for RSV.

Doctors say there are a few reasons for that. Trials for the first RSV vaccine, developed in the 1960s, had tragic consequences: Two of the children who participated died and around 80% were hospitalized, said Green. 

Green added that because the virus only infects humans, it hasn't been possible to develop drugs and vaccines using animal models, which is the standard way to design medication and inoculations for viral illnesses. 

Additionally, Chiu said, the virus has developed ways to interfere with the immune system and re-infect people over the course of their lives. Even after infection, people don't have the immunity needed to prevent them from catching RSV again.

The virus's reinfection ability has made it "very difficult for us to understand what factors you need to stimulate to give you protection," said Chiu. "It's only been in recent years that we've really started to understand that in detail."

Chiu said there are a few vaccines that look promising — vaccines produced by pharmaceutical companies Pfizer and GSK have seen positive results of more than 80% effectiveness in recent trials — and could be licensed in the next three to five years. They are targeted at older people and pregnant women, rather than babies and infants.

Risks are often higher in these groups and, as mentioned above, babies' immune systems are underdeveloped. That makes it difficult to calculate how to trigger an appropriate immune response — the production of antibodies to fight a RSV infection.

"In young babies, the alternative is to give them antibodies in an injection," Chiu said. "So, rather than giving them a vaccine, which triggers your own body to make the antibodies, you can make the antibodies in the lab and just give the antibodies to babies."

There are some antibody treatments in the pipeline that have successfully worked to protect premature infants from serious cases of RSV in trials, Chiu said, but they are not widely available yet.

 

How do you protect yourself against RSV?

Chiu said the best way to reduce transmission of RSV is to avoid people who have symptoms and to wash your hands regularly. 

How many children die from RSV per year?

Although some models say that globally around 120,000 infants die from RSV every year, a study  published early in 2022 by researchers at the Boston University School of Medicine suggests the number could be much higher.

The 120,000 figure is based on modeling conducted in hospital-based settings — generally in higher-income countries — and does not account for RSV deaths that occur outside the hospital, the researchers said.

In order to get a sense of how many infants died of RSV in non-hospital settings, the researchers partnered with mortuary staff in Lusaka, Zambia, to test around 2,200 deceased infants, which represented around 80% of infant deaths in the city between August 2017 and August 2020.

The study showed that RSV directly caused 4.7% of all infant deaths that occurred outside of hospitals, indicating that the modeled global mortality rates are probably lower than the true figure.

Edited by: Zulfikar Abbany