Do All Babies Congenitally Infected with Zika Develop Microcephaly?

Pedro Fernando da Costa Vasconcelos, MD, PhD, director of WHO Collaborating Center for Arbovirus and Research, Evandro Chagas Institute, discusses the likelihood that fetuses congenitally infected with the Zika virus will develop related complications, such as microcephaly.

Interview Transcript (slightly modified for readability)

“[Will] all babies [congenitally infected with Zika virus] develop [complications]? No. You have [a] cohort of pregnant women [from] different places in Brazil that have been followed and we have observed, ourselves and [from] others’ research, that only a small percentage of pregnant women will transmit the virus to [their] fetuses, and the babies will [be] born with microcephaly. Different studies [have] estimated [that] between 1% [and] 13% of these babies will develop severe malformation and microcephaly; not all pregnant women [infected during pregnancies] will [cause] severe [complications] for their babies.

I think that it’s important to remember that almost all infectious disease [have] a large range that range from asymptomatic infections to severe, fatal disease. It’s interesting to observe that, for example, that the percentage of severe disease [resulting from a Zika virus infection], is around 1%, [for] yellow fever [it’s] around 15%. So now, trying to estimate the severity of [Zika virus infection], I’m sure that not all fetuses that [are] infected will present [with] severe disease. It’s important to [keep] this in mind, because the number of infected babies that will not present [with complications] perhaps can be higher than the number of babies that will present [with] severe disease, like microcephaly or other malformations. This is natural because all infectious diseases have a range of the disease’s severity. In [the] case of Zika, it is estimated that around 80% of all infections will be asymptomatic, [meaning infection] will not cause symptoms.”