Approximately 80% of patients are asymptomatic, and those with symptoms generally experience a mild, self-limited illness lasting 2 to 7 days.[13][150] Severe disease requiring hospitalisation is uncommon and the case fatality is low.[13] The presence of comorbidities may increase the risk of a fatal outcome, based on a few case reports.[14] However, fatal outcomes have been reported in healthy individuals.[208] No fatalities have been reported in children.[149] The Centers for Disease Control and Prevention (CDC) confirmed the first Zika-related death in the Continental US in an elderly resident of Utah who contracted the virus during travel to an area with active transmission. The patient also had an undisclosed health condition and the exact cause of death is unknown.[209]

Prognosis for infants born with microcephaly is unclear; however, microcephaly due to other causes is associated with a range of neurodevelopmental issues. An estimate of the case fatality rate for infants with microcephaly associated with Zika virus infection is 8.3%.[210] A study in 19 infants born with microcephaly in Brazil found that most infants had severe motor impairment and other functional difficulties at 19 to 24 months of age, including seizure disorders, respiratory disorders, hearing/vision impairment, and sleeping/feeding difficulties. These outcomes often occur together.[211]

A study of 1450 infants that used data from a US Zika registry found that 14% of 1-year-old children who were exposed to Zika virus in utero had health issues potentially related to virus exposure. Of these infants, 6% had at least one Zika-associated birth defect, 9% had at least one neurodevelopmental abnormality possibly associated with Zika virus exposure, and 1% had both. However, the authors noted that most children did not have evidence of all recommended evaluations, and therefore, additional anomalies may exist.[212]

Once people have recovered from infection, they are likely to be protected from future infections. There is no evidence to suggest that prior Zika virus infection poses a risk for birth defects in future pregnancies.[213]

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