'Silent spread': RSV moves through postpartum care centers without symptoms — and two antibody shots raise new questions

Alarm is growing over the "silent spread" of respiratory syncytial virus, or RSV, through postpartum care centers — communal living spaces for newborns — where the virus moves without visible symptoms. With nearly half of infected infants showing no signs of illness while most symptomatic cases escalate directly to severe disease requiring hospitalization, experts say routine temperature checks are no longer enough. They are calling for diagnostic testing at admission and systematic tracking of preventive antibody shot records.

An epidemiological investigation into a recent RSV outbreak at a domestic postpartum care center found that 9 of 18 newborns at the facility had been infected. Of those, 4 — or 44.4 percent — showed no discernible symptoms.

Among the five infants who did develop symptoms such as coughing or phlegm, four — 80 percent — required immediate hospitalization. Detailed diagnoses revealed two cases of bronchiolitis, two of pneumonia and one suspected case of sepsis, confirming that RSV can rapidly progress to life-threatening illness in infants whose immune systems are not yet fully developed.

Analysts say the outbreak reflects not poor management but the virus's inherent capacity for silent transmission. Because surveillance systems focused on isolating symptomatic patients cannot detect early-stage outbreaks, comprehensive contact testing and continuous monitoring are considered essential.

RSV is particularly contagious even among pediatric respiratory pathogens. During peak season, a single patient can infect roughly three others, and an estimated 90 percent of children under 2 are infected at least once. The virus spreads not only through coughs and sneezes but also survives on hard surfaces such as tables and plastic for more than six hours, making transmission via contaminated objects common.

Compounding the challenge is the virus's incubation period — typically four to six days — and the fact that spread can originate from asymptomatic carriers, making outbreaks difficult to detect early. A community birth cohort study tracking 158 infants over their first year of life found that 12 of 54 initial RSV infections — 22.2 percent — involved viral detection with no respiratory symptoms. That is why temperature checks and basic symptom screening alone cannot reliably prevent the virus from entering a facility.

Experts recommend that postpartum care centers enforce thorough handwashing, regular disinfection of utensils and shared items, restricted access for symptomatic visitors, and greater use of rooming-in arrangements. They also say centers should conduct proactive RSV testing at admission to catch asymptomatic carriers, and should provide parents with information about preventive antibody shots to encourage active protection.

Two RSV preventive antibody shots are currently available for newborns and infants in South Korea: Beyfortus, which has been prescribed since 2025, and a second product that received Ministry of Food and Drug Safety approval in June. Both offer season-long protection with a single dose for infants entering their first RSV season, but they differ in mechanism, dosage and safety profile.

A particularly important consideration for postpartum care centers is whether either shot interferes with rapid antigen test results. According to Ministry of Food and Drug Safety approval documentation, Beyfortus does not affect rapid antigen test outcomes. The second product, however, is noted to potentially cause false negatives — where an infected infant tests negative — in some tests after administration. If a newborn who received that shot is admitted to a postpartum care center, relying solely on a rapid antigen test result could allow the virus to go undetected; staff should verify vaccination history in advance and, where necessary, supplement testing with PCR.

For high-risk children under 24 months who face elevated risk of severe disease during a second RSV season, Beyfortus holds an approved indication for an additional dose, while the second product does not. That difference means the choice of shot should be tailored to each infant's age and health status.

Experts recommend that infants born between October and March — during the RSV season — receive the antibody shot within the first week of life, while those born between April and September should be vaccinated in late September to early October, just before the season begins.