“When the virus infects someone it usually gets in through the nose,” said researcher Nathalie Mielcarek who is working with the Lille Pasteur Institute to develop a nasal spray vaccine against whooping cough.

“The idea is to shut the door.”

An article published in Scientific American in March urged developing nasal spray vaccines because they have an immediate effect on the virus in an infected person’s mucus.

There they trigger production of an antibody known as immunoglobulin A, which can block infection.

“This overwhelming response, called sterilising immunity, reduces the chance that people will pass on the virus,” said the article.