Respiratory syncytial virus (RSV) causes about 33 million episodes of lower respiratory illness (LRIs) and up to 118,200 deaths annually. The goal of a new study published in Open Forum Infectious Diseases was to evaluate LIDcp∆M2-2, a version of LID∆M2-2 (a candidate vaccine with M2-2 deletion), that was further attenuated by an additional set of 5 well-characterized attenuating mutations derived from cold-passaged (cp) RSV [12, 13] in RSV-seronegative children aged 6–24 months. Here, RSV-seronegative children, aged 6-24 months, received either a single intranasal dose of 105 plaque-forming units (PFU) of LIDcpΔM2-2 or a placebo. RSV serum antibodies, vaccine infectivity, and reactogenicity were assessed. The results showed that 36% vaccinees shed vaccine virus with median peak titers of 1.6 log10 PFU/mL by quantitative culture and 4.5 log10copies/mL by polymerase chain reaction; meanwhile, 45% had ≥4-fold rise in serum-neutralizing antibodies. However, respiratory symptoms or fever were common in vaccinees (64%) and in placebo recipients (6/6, 100%). From the findings, it was concluded that RSV LIDcpΔM2-2 is overattenuated.