Fix disfluencies in the sentence: Smallpox vaccine is the first vaccine that people used to improve immunity to a certain disease.
The vaccine was developed in 1970s, but it was not approved until 1980.
The vaccine was developed by the US National Institutes of Health, and it was approved in 1980.
The vaccine was developed by the US National Institutes of Health, and it was approved in 1980.
The vaccine was developed by the US National Institutes of Health, and it was approved in 1980.
The vaccine was
The vaccine is the first vaccine that has been developed to prevent the disease.
The vaccine is the first vaccine that has been developed to prevent the disease.
The vaccine is the first vaccine that has been developed to prevent the disease.
The vaccine is the first vaccine that has been developed to prevent the disease.
The vaccine is the first vaccine that has been developed to prevent the disease.
The vaccine is the first vaccine that has been developed to prevent the disease.
The vaccine is the