Is it or is it not? Lessons learned from a case of suspected vaccine-associated measles

Abstract

Background: Measles is a highly infectious viral disease that can cause serious illness and complications. Despite Australia's measles elimination status declared in 2014, the risk of acquiring measles through importation by overseas travellers who are non-immune remains. Identifying wild-type measles in a female who was recently vaccinated with measles mumps rubella (MMR) is a challenge one metropolitan Public Health Unit (PHU) experienced. Case Description: In 2018, a metropolitan Sydney PHU was notified of a positive polymerase chain reaction (PCR) result for measles on a nasopharyngeal swab for a 32 y old female who had recently received an MMR-II vaccination seven days prior to developing symptoms of measles. The case had no known epidemiological link, no recent overseas travel and no contact with recent measles cases during her incubation period. The reference laboratory ran sequencing on the clinical specimen to distinguish between wild-strain and vaccine-type measles. The results of this were inconclusive, however given the recent vaccination and inconsistent clinical symptoms and no identified epidemiological link, a decision was made to re-run the genotyping, collect additional specimens for testing, and quarantine the case until a definitive result was obtained. Subsequently, sequencing and genotyping test results revealed that this indeed was a wild-type measles strain, genotype D8. Discussion: A change in the epidemiology of measles, especially in low incidence countries like Australia, means distinguishing between wild type and vaccine–associated measles has become a new challenge, but critical in implementing a timely public health response. The initial decision to classify this case as vaccine-associated measles was based on the clinical context, epidemiological risk and inconclusive sequencing results. The lack of an epidemiological link created confusion for public health staff when investigating this case. Conclusion: This case investigation and response has demonstrated the challenge for public health with non-typical presentations of wild-type measles, particularly in people who have received one MMR. The reflection of the public health management of this case has provided an opportunity to learn from this experience and can become a valuable teaching tool for public health professionals globally, particularly in low incidence measles countries.