Analyze This: Zika and microcephaly

Hoping to learn more about Zika, scientists compared spikes in infections and in a birth defect

zika timelag

Zika infections among pregnant women (solid line and scale on left) in the nation of Colombia spiked in January 2016 (around week 4). About six months later, the country saw a drastic increase in the number of infants and fetuses with microcephaly (dotted line and scale on right). 


Zika is a viral disease that humans can contract after being bitten by mosquitoes. It is a very serious problem for pregnant women and their babies. Evidence has been mounting that this virus can cause a birth defect called microcephaly. Babies born with the condition have abnormally small heads and other problems. Scientists at the Centers for Disease Control and Prevention (CDC) and elsewhere have been collecting data on Zika and how it is impacting families.

This graph takes data collected in Colombia on pregnant women, fetuses and infants. Zika has taken a big toll in this South American country. The number of babies born with microcephaly in 2016 there was four times what it was in 2015. In the graph, the rate of pregnant women infected with Zika is shown with a solid line. The rate of infants and fetuses who had microcephaly in Colombia from 2015 to the end of 2016 is shown with a dotted line.

“This provides very compelling evidence that every country that experiences a large Zika outbreak is likely to see devastating outcomes on fetuses and infants,” says CDC epidemiologist Peggy Honein.

Data dive:

How does this graph support what the scientist said?

When was the largest spike in reports of pregnant women with Zika? How many women were diagnosed with the disease?

When was the largest spike in reports of infants and fetuses with microcephaly?

How many weeks apart are these events?

Was this graph difficult to understand? Why?

Is there a way to improve this graph or make it easier to read?

Analyze This! explores science through data, graphs, visualizations and more. Have a comment or a suggestion for a future post? Send an email to

Lillian Steenblik Hwang is the associate digital editor for Science News for Explores. She has a bachelor's degree in biology (and a minor in chemistry) from Georgia State University and a master's degree in in science journalism from Boston University.

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