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On March 29th 2015, Brazil first notified the World Health Organization (WHO) of an unknown illness characterized by skin rash, which was rapidly spreading in the northeast of the country. In 4 months, nearly 7000 mild cases were reported with no causalities among them and symptoms were mild and appeared not too problematic. However, in October 2015, researchers from the northeaster state of Pernambuco, in Brazil notify an unusual increase in the number of cases of microcephaly among new-borns, which led authorities to declare, a month later, a state of national public health emergency as cases of microcephaly continued to increase. Scientific evidence confirmed that the cause of microcephaly outbreak in northeast Brazil was Zika virus infection during pregnancy. WHO deemed the Zika outbreak as Public Health Emergency of International Concern, the fourth declared since 2009, prompting international response and mobilization.

For the period of uncertainty (and beyond) of what was causing the microcephaly outbreak, alternative hypothesis spread via rumours. These were communicated not only in person but also in social media, where they were amplified – recent data published by Facebook Brazil identified that rumours were among three out of the ten most shared content about Zika on the platform. One of the main rumours circulating at the time was that an expired batch of vaccines administered by the government was responsible for microcephaly. Despite scientific evidence of link between Zika during pregnancy and microcephaly, recent qualitative interviews point to a lingering suspicion of a link between vaccines and



After its peak in 2015 and 2016, suspected and confirmed cases of Zika have fallen drastically, bringing less attention from the media and general public. However, we do not know if there is substantive, lasting immunity to Zika in the population and vector control measures, despite intensified during the epidemic, have had suboptimal results. There is an urgent call for a Zika vaccine as herd immunity achieved by a successful Zika immunization would have a positive long-term impact in the population. There is a rush for a vaccine now, with human trials in place and a vaccine predicted for the next years. Therefore, there is the need for research addressing the social context in which the Zika epidemic took place and how it mediates confidence in a Zika vaccine.


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