Only those who naturally caught mumps or whooping cough as a child have complete, and lifelong, immunity, but mass vaccination programmes mean they are becoming a diminishing minority of the population. Routine vaccination will never be able to offer similar protection, say researchers from the University of Michigan.
Cases of whooping cough have been steadily rising in the US since the 1970s, and this is because the newer acellular version of the DPT (diphtheria- pertussis-tetanus) vaccine is "imperfect", said lead researcher Aaron King.
Although they based their conclusions on data from Massachusetts, the researchers said a similar phenomenon will be seen across all the US and Western Europe, which have also adopted the acellular vaccine.
"This resurgence is the predictable consequence of rolling out a vaccine that isn't quite perfect and not hitting everybody in the population," said Dr King.
The vaccine provides up to 10 years' protection against whooping cough, slightly better than the five to seven years protection that earlier studies had suggested, the Michigan researchers say.
Cases of mumps are also increasing and have been for the past decade—and it could be because the body's response to the MMR (measles-mumps-rubella) vaccine has weakened significantly, say researchers at the Harvard T H Chan School of Public Health.
The resurgence is being seen in people aged between 18 and 29, the vast majority of whom had the recommended two shots when they were small children. This puts around one-third of 10-to-14-year-olds at risk of getting mumps, the researchers warn.
The only ones who don't have to worry are those who caught mumps when they were children, and who have natural immunity.