Abstract
On 21 January 2019, public health authorities of two neighboring Austrian provinces reported an increase in measles cases. We investigated this occurrence to identify clusters of epidemiologically linked cases and the associated vaccination status in order to generate hypotheses on those factors explaining the size of the measles clusters. Probable cases were residents of the provinces of Styria or Salzburg with clinical presentation of measles after 1 January 2019 who were linked to a confirmed case using RNA virus detection. We collected data on age, rash onset, certificate-based vaccination status and reasons for being unvaccinated. Contact history was used to identify chains of transmission. By 11 March, we identified 47 cases, with 40 (85.1%) in unvaccinated patients. A cluster of 35 cases with a median age of seven years (IQR: 1-11) occurred between 9 January and 20 February in the province of Styria due to one transmission chain with four case generations. Of 31 vaccine-eligible cases, 25 (80.6%) were unvaccinated, of which 13 refused vaccination. Between 10 January and 1 March, we identified 12 cases as part of five unlinked clusters in the province of Salzburg. Each of these five clusters consisted of two generations: the primary case and the successive cases (median age: 22 years, IQR: 11-35). Eleven of 12 cases occurred in unvaccinated patients, with none of the 11 having a vaccination-refusing attitude. An extended measles cluster in a vaccination-refusing community, compared to five short-lived clusters concurrently occurring in the neighboring province, illustrates how vaccine refusal may hamper control of transmission.