evidence: Two people who received Pfizer’s respiratory syncytial virus (RSV) vaccine during a clinical trial were later diagnosed with Guillain-Barre syndrome, and the US Food and Drug Administration has asked Pfizer to conduct a safety study if the shot is approved, according to agency documents released Friday. [...] RSV is a highly contagious virus that causes flu-like illness in people of all ages that increases in severity with age. According to the US Centers for Disease Control and Prevention, RSV is responsible for an estimated 177,000 hospitalizations and 14,000 deaths per year among adults 65 or older. [...] GSK’s RSV vaccine candidate for older adults was 94.1% effective at preventing severe lower respiratory tract disease and 82.6% effective in preventing illness overall. The company similarly reported a potential case of Guillain-Barre syndrome among vaccine recipients but said there was insufficient evidence to confirm a diagnosis. The FDA considers the case to be related to the vaccine and said it will review GSK’s safety plan.