Health officials from Colombia and the U.S. Centers for Disease Control and Prevention followed 550 pregnant Colombians who “reportedly contracted” the virus during the third trimester of pregnancy.
Researchers are still following 532 pregnant women who were diagnosed with Zika in the first trimester, 702 women diagnosed in the second trimester, and 50 additional women who were diagnosed in the third trimester. However, because these women have not given birth, no information is available yet on how many of their children will be found to have microcephaly.
Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, said the early findings seemed promising but that it was far too preliminary to change guidelines based on data.
"I'm looking for good news wherever I can find it," Schaffner said. "I have all my fingers crossed and I'm waiting for more information as it develops.”
Schaffner pointed out that health officials have been seeking more information about which women were most at risk for having children with microcephaly.
The findings are still preliminary and health officials have said research will need to continue for years to see if children without microcephaly have other developmental delays.
Colombian health officials, who separately track the number of microcephaly cases in the country, independently found 50 babies born with microcephaly during the study period, from August 2015 to April 2016. Four of these babies tested positive for Zika. However, their mothers did not experience symptoms and thus were not included in the original study. Of the rest, 20 cases were linked to other causes, and 26 are still under investigation.
The study authors also found that women tested positive for Zika more often than men, but clarified it was likely because women were coming in more to get tested due to the virus' effect on pregnancy.
The Zika virus usually results in minor symptoms, including fever, rash, joint pain and conjunctivitis, according to the CDC. Approximately one in five people infected with the virus show symptoms. Severe complications from the virus that require hospitalization are rare, according to the CDC.