Respiratory syncytial virus (RSV) is spreading across parts of the Southern United States during an unusual time of year, the Centers for Disease Control and Prevention (CDC) warned last week.
On June 10, the CDC issued a health advisory alerting health care providers and caregivers about an unseasonable rise in cases of RSV, a common, flu-like respiratory illness that is usually mild but can cause serious sickness in vulnerable populations—including babies, young kids, and older adults who have chronic medical conditions. And according to the advisory, babies and toddlers may be at particularly high risk for severe illness as we continue to emerge from the pandemic.
RSV usually peaks during cold and flu season in the U.S., but we didn’t see that pattern this year. Cases dropped off sharply in April 2020 and stayed low through this fall and winter, according to the CDC. RSV mostly spreads via respiratory droplets (from coughing or sneezing) and direct contact with a contaminated surface, so the unusually low infection rates are probably thanks to public health measures taken during the pandemic, like wearing masks, social distancing, avoiding indoor crowds, and increased hand washing.
Then, in March 2021 (around the time that many states began lifting COVID-19 restrictions), we started to see an uptick in lab-confirmed cases of RSV. CDC surveillance data show that case numbers and positive test rates have been increasing in states throughout the southern U.S., including Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas. (The agency notes that data for the past few weeks is probably still incomplete.) Since this is such an atypical timeline for RSV transmission, the CDC says they can’t predict how much more the virus is going to spread, or for how long. According to the advisory, data show that parts of Australia saw a similarly unseasonal rise of RSV in late 2020, and South Africa in early 2021—although the virus hasn’t reached typical peak levels in most places.
RSV is a common virus, particularly among babies and young children. In fact, nearly all kids will get an RSV infection at some point by age 2, according to the CDC. While most cases are mild, RSV can sometimes cause serious illness, particularly in babies and people over 65. The virus is the number one cause of the lung infections bronchiolitis and pneumonia in infants under 1 year, according to the CDC. Data suggest that RSV is responsible for an average of 58,000 hospitalizations and 100 to 500 deaths in kids under age 5 every year, according to the CDC (as well as 177,000 hospitalizations and 14,000 deaths in people 65 and older).
The CDC is particularly concerned that the pandemic has put older babies and toddlers at risk for severe illness connected to RSV. Since there was much less of the virus circulating this fall and winter than usual, the advisory explains, the immune systems of most infants and toddlers have had less exposure to the pathogen. That means they probably haven’t had as much of a chance to build up immunity, and could therefore be at elevated risk for serious illness related to RSV (like a lung infection).
While RSV typically presents with flu-like symptoms in adults (including runny nose, coughing, sneezing, wheezing, sore throat, fever, headache, fatigue, and decreased appetite), the illness can be less obvious in kids and babies. In infants younger than six months, there may only be vague symptoms: irritability, feeding less than usual, lethargy, labored breathing, and fever. Meanwhile, older babies, toddlers, and young kids might first experience a runny nose and reduced appetite, followed by sneezing, coughing, wheezing, or fever one to three days later, the CDC explains.