Some 38% of U.S. multinationals, universities and non-profits surveyed by an arm of the State Department are allowing female employees to defer travel or leave countries where the Zika virus has been reported.

A fifth of the 321 respondents said they were giving male employees similar options, a sign of how employers’ travel policies are diverging as they react to the mosquito-borne virus and uncertainty about the way it is transmitted.

Scientists are investigating a potential link between Zika infections of pregnant women and more than 4,000 suspected cases in Brazil of microcephaly, a condition marked by abnormally small head size that can result in developmental problems.

The State Department’s Overseas Security Advisory Council (OSAC), which has a membership of more than 3,500 U.S. companies and institutions that do business abroad, surveyed its members and reported the results on Feb. 5.

Boeing Co (BA) , Microsoft Corp (MSFT), Walt Disney Co (DIS) and others assist OSAC, according to its website.

The largest share of the survey’s respondents, none of whom were identified, were only recommending ways employees can avoid mosquito bites or inform themselves via the U.S. Centers for Disease Control and Prevention (CDC) or the World Health Organization (WHO).

Multinational companies contacted separately by Reuters showed a similar split over how to respond to the virus’s rapid spread in Latin America and the Caribbean.

While airlines and cruise ship operators have yet to report declines in bookings because of the disease, that may be in store if the virus lingers, Credit Suisse analyst Julie Yates said in a research note on Thursday.

In line with CDC guidance, Wal Mart Stores Inc (WMT), American Express Co and snack-maker Mondelez International Inc (MDLZ) have told workers who are pregnant or considering pregnancy to consult with health professionals before visiting any of the 26 countries and territories where Zika is active. The WHO declared an international emergency for Zika on Feb. 1, but much remains unknown about the virus.

Chevron Corp (CVX), which has significant operations in Brazil and Venezuela, is among companies with a more expansive policy that allows any concerned employee to opt out of travel, spokesman Kurt Glaubitz said.

By contrast, Ford Motor Co (F), General Motors Co (GM) and security products company Allegion PLC have told employees about precautions for travel but they have not publicly disclosed policy changes for women of child-bearing age.

U.S. companies have reacted faster than during past epidemics, such as the two-year-long outbreak of Ebola in West Africa that began in December 2013, because Zika is spreading in their backyard, said Christopher Pardee, manager of health intelligence at travel risk consultancy iJET.

Some 41% of Americans aware of the disease have said they are less likely to take a trip to affected regions, a Reuters/Ipsos poll found a week ago.