The US has approved the first vaccine for respiratory syncytial virus (RSV) for people aged 60 and over.
On Wednesday the Food and Drug Administration (FDA) approved the use of Arexvy in the country.
The vaccine is said to protect older adults against the respiratory virus.
Now the Centers for Disease Control and Prevention (CDC) must decide if every senior really needs RSV protection or only those considered at high risk from RSV.
In June 2023, the Advisory Committee on Immunization Practices (ACIP) will decide on the appropriate use of the vaccine in the US.
RSV is a "highly contagious" virus that causes infections of the lungs and breathing passages.
It is very common and spreads easily in coughs and sneezes. Almost all children have had it by the time they're two years old, according to the NHS.
In older children and adults, RSV may cause a cough or cold, but in young children, it can cause bronchiolitis - a chest infection that, although common, can sometimes be serious.
The CDC said most adults who get RSV have a mild illness that might last between one to two weeks.
However, some people may experience a more severe RSV infection.
What you need to know about Arexvy
The FDA approved Arexvy for the prevention of lower respiratory tract disease caused by RSV in individuals who are 60 years of age and older.
Pharmaceutical firm GSK said after its third trial, "the vaccine showed statistically significant and clinically meaningful overall efficacy... against RSV-LRTD in adults aged 60 years and older".
The firm also said the vaccine was "generally well tolerated with an acceptable safety profile".
After analysing the safety and effectiveness of the vaccine, the FDA said: "The safety and effectiveness of Arexvy is based on the FDA's analysis of data from an ongoing, randomised, placebo-controlled clinical study conducted in the U.S. and internationally in individuals 60 years of age and older."
Dr Phil Dormitzer, GSK's senior vice president and global head of vaccines research and development, said the company is already manufacturing doses of the vaccine
Why has it taken so long to come up with a vaccine?
There was a major setback in the 1960s after an experimental shot worsened infections in children.
However, scientists have now figured out a better way to develop these vaccines.
GSK's new vaccine for older adults helps train the immune system to recognise a protein on RSV's surface, and contains an ingredient that develops a stronger immune reaction.
A clinical study of Arexvy will look at the safety and effectiveness of a single dose administered to individuals 60 years of age and older.
Participants will remain in the study through three RSV seasons - three years - to assess the duration of effectiveness, and the safety and effectiveness of repeat vaccination.
The FDA has now analysed data for a single dose of Arexvy from the first of the three RSV seasons of the study.
There were approximately 12,500 participants that received the vaccine and 12,500 participants received a placebo.
People who received the vaccine significantly reduced the risk of developing RSV-associated lower respiratory tract disease (LRTD) by 82% and reduced the risk of developing severe RSV-associated LRTD by 94%.
What are the side effects?
The studies found the side effects of the vaccine were limited.
But the most commonly reported side effects by people who received Arexvy were:
• Muscle pain
• Joint stiffness
• Joint paint
The FDA noted a higher incidence of atrial fibrillation (irregular heart rhythm) among vaccine recipients relative to the control group.
It also identified one case of Guillain-Barré syndrome - a rare neurological disorder that damages nerve cells and causes muscle weakness or paralysis - that was potentially related to the vaccine.
Dr Dormitzer said it's difficult to know what to make of the Guillain-Barré case but added: "I would not say it's a great concern at this point."
'An important public health achievement'
Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said the approval of the vaccine is "an important public health achievement to prevent a disease which can be life-threatening".
He added: "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."
What are some of the symptoms of RSV?
According to the CDC, people usually show symptoms within four to six days after getting infected - some of these might include:
• A running nose
• A decrease in appetite
The CDC website said these symptoms "usually appear in stages and not all at once".
It added: "In very young infants with RSV, the only symptoms may be irritability, decreased activity, and breathing difficulties."