In the long human effort to shield the vulnerable from respiratory illness, a South Korean biotech has cleared a meaningful early threshold: its experimental RSV vaccine, EuRSV, moved through its first human trial without serious harm and with the immune system responding as hoped. One hundred adults across a wide span of life's ages participated, and the data now filed with regulators suggests the science is sound enough to carry forward. The choice of which formulation to advance — one stronger in antibodies, one deeper in cellular defense — is itself a reminder that medicine is rarely a sin