A third dose of measles vaccine may need to be considered in future, Australian researchers say, after finding evidence of increasing secondary vaccine failure because of waning immunity.

Researchers from the Victoria Government’s health protection branch and the Doherty Institute have identified 13 cases of measles occurring in adults despite partial — and in one case full — immunisation between 2014 and 2017.

No such cases occurred in the preceding six years, they say, suggesting secondary vaccine failure is likely emerging as a problem for all countries that have eliminated the disease as there is no natural boosting from exposure to circulating wild-type virus.

“Our findings challenge the assumption of immunity among those who are fully vaccinated against measles and those with measles-specific IgG,” the authors say.