The first case of Zika virus in humans was documented in 1960. For decades, Zika remained in obscurity until an outbreak on the island of Yap in 2007. Another epidemic occurred on French Polynesia in 2013, that reached Brazil in 2014. In 2016 over 20 countries in the Americas have Zika transmission. What changed?
It is possible that the virus has mutated to a more virulent form.
The virus could have mutated to a form that has greater transmission.
The human population in the Americas may be more susceptible to the virus.
Answers to these questions could help predict the trajectory for Zika.
Does Zika cause microcephaly?
We don’t know. There is a spike in microcephaly in Brazil that coincides with the spread of the Zika virus. Zika has been found in amniotic fluid and in the brains of babies with microcephaly who have died. Both in the 2013-14 outbreak in French Polynesia and in the 2014-15 outbreak in Brazil increases in birth defects are noted. This correlation is worrisome, but correlation is not causation. It will take further research to determine causation.
Microcephaly is difficult to diagnose. In reviewing the 4000 cases of microcephaly in Brazil, 260 cases have been confirmed and 462 reclassified. Only 6 cases of microcephaly have been positively linked to Zika so far. We await further investigation that could confirm evidence in other cases. The absence of evidence is not evidence of absence.
Was the decision to declare a public health emergency warranted?
In assessing risk, the severity of outcome must be considered. The long term consequences of microcephaly are severe. The uncertainty about the effects of Zika are large. Thus, it is good policy to urge caution while intensifying the research into the important unanswered questions so we can make more informed policy decisions.