Every year in the United States, respiratory syncytial virus (RSV) causes between 110,000-180,000 hospitalizations and 6,000-10,000 deaths in adults over 50 years of age. To determine the impact of an RSV prefusion protein vaccine, researchers in Denmark randomized 131,000 adults greater than 60 years of age to receive either RSV vaccine or placebo (Lassen MCH, et al. RSV prefusion F vaccine for prevention of hospitalizations in older adults. N Engl J Med. 2026 Jan 8;394(2):138-151).
Of interest, the RSV prefusion F vaccine had already been shown to prevent lower respiratory tract disease and acute respiratory illness in adults more than 60 years of age in a previous study (Walsh EE, et al. Efficacy and safety of a bivalent RSV prefusion F vaccine in older adults. N Engl J Med. 2023. Apr 20;388(16):1465-1477). The purpose of this trial in Denmark was to show that the RSV vaccine could also prevent hospitalizations caused by RSV. Given that prevention of hospitalizations could have been assumed from the previous study, people could reasonably argue that the Danish trial, which included a placebo arm, was unethical.
The Denmark researchers found that the RSV vaccine was 83.3% effective at preventing hospitalizations from RSV respiratory tract infections and 91% effective at preventing hospitalizations from RSV lower respiratory tract infections, confirming prior studies. The RSV vaccine was also 28% effective at preventing respiratory tract disease of any cause. The incidence of serious adverse events was the same in the vaccine and placebo groups.
Every year in the United States, respiratory syncytial virus (RSV) causes between 110,000-180,000 hospitalizations and 6,000-10,000 deaths in adults over 50 years of age. To determine the impact of an RSV prefusion protein vaccine, researchers in Denmark randomized 131,000 adults greater than 60 years of age to receive either RSV vaccine or placebo (Lassen MCH, et al. RSV prefusion F vaccine for prevention of hospitalizations in older adults. N Engl J Med. 2026 Jan 8;394(2):138-151).
Of interest, the RSV prefusion F vaccine had already been shown to prevent lower respiratory tract disease and acute respiratory illness in adults more than 60 years of age in a previous study (Walsh EE, et al. Efficacy and safety of a bivalent RSV prefusion F vaccine in older adults. N Engl J Med. 2023. Apr 20;388(16):1465-1477). The purpose of this trial in Denmark was to show that the RSV vaccine could also prevent hospitalizations caused by RSV. Given that prevention of hospitalizations could have been assumed from the previous study, people could reasonably argue that the Danish trial, which included a placebo arm, was unethical.
The Denmark researchers found that the RSV vaccine was 83.3% effective at preventing hospitalizations from RSV respiratory tract infections and 91% effective at preventing hospitalizations from RSV lower respiratory tract infections, confirming prior studies. The RSV vaccine was also 28% effective at preventing respiratory tract disease of any cause. The incidence of serious adverse events was the same in the vaccine and placebo groups.