The U.S. Food and Drug Administration on Wednesday approved the first RSV vaccine in the U.S.

Scientists have been trying to develop an RSV vaccine for decades after previous high-profile attempts failed.

The vaccine, made by the pharmaceutical company GSK, is for older adults. Pfizer and Moderna are also developing similar RSV vaccines.

The Centers for Disease Control and Prevention still needs to weigh in with specific recommendations, which is expected in June. GSK anticipates it will have enough vaccine to meet demand in time for the fall and winter respiratory illness season.

GSK said it has "millions of doses ready to be shipped."

Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said in a statement: "Older adults, in particular those with underlying health conditions, such as heart or lung disease or weakened immune systems, are at high risk for severe disease caused by RSV. Today's approval of the first RSV vaccine is an important public health achievement to prevent a disease which can be life-threatening and reflects the FDA's continued commitment to facilitating the development of safe and effective vaccines for use in the United States."

RSV is a viral infection that leads to mild illness for most people; however, it can be dangerous for older adults and some young children. RSV is a common cause of lower respiratory tract disease (LRTD), which affects the lungs and can cause life-threatening pneumonia and bronchiolitis, according to the FDA.

Each year between 60,000 and 120,000 older adults are hospitalized due to RSV.

RSV circulation is seasonal, typically starting in the fall and peaking in the winter. Pharmaceutical companies are also working on RSV vaccines that are targeted at young children.