(CNN) The proportion of Zika-related birth defects during 2016 was nearly 20 times higher than the number seen during the pre-Zika years, according to a new report from the United States Centers for Disease Control and Prevention. In particular, brain abnormalities or microcephaly, where a baby's head size is smaller than expected, occurred about 33 times as often in pregnancies with Zika infections than in the pre-Zika years. Zika, a virus transmitted primarily by mosquitoes and unprotected sex, has been spreading around the globe with locally transmitted cases in the US were first reported in Florida and Texas during 2016. Currently, there is no vaccine to prevent infection.Brain abnormalities or microcephaly occurred about 33 times as often in pregnancies with Zika infectionsNew report is based on data from surveillance programs in three US states 
 Question:When families learn their child has a birth defect like those associated with _ virus infection, they experience a grief reaction similar to when they lose a child, he said.
Zika