People who have had the pertussis (whooping cough) vaccine are still catching the disease, but they don't have any symptoms, say researchers from the Sante Fe Institute.
They could be acting as carriers, and are one reason why whooping cough cases have suddenly increased dramatically. In 2012, there were 50,000 new whooping cough infections in the US, the highest since 1955.
This sudden rise has baffled health officials, who have variously blamed the ineffectiveness of the current DTaP vaccine, which includes the pertussis jab, as well as the anti-vaccine people who may have refused it for their children.
But Ben Althouse and Sam Scarpino from the institute reckon the problem may lie among those already vaccinated, and who are carrying the disease. And the number of those who are infected but have no symptoms could be many times that of those who do have symptoms.
The researchers reckon it could be to do with the new vaccine that doesn't block transmission (and nor does it appear to protect against the disease itself). The acellular vaccines were introduced in the 1990s after it was found the original vaccine, which used inactivated pertussis cells, was also causing unacceptably high numbers of adverse reactions.
"There could be millions of people out there with just a minor cough, or no cough, spreading this potentially fatal disease without knowing it," said Althouse.
(Source: BMC Medicine, 2015; 13: 146)