Health officials in the U.S. and abroad are urging anyone who has traveled to areas affected by the Zika virus to wait a month before giving blood.

On Wednesday, the U.K.'s National Health Service became the latest organization to put in place a 28-day “self-deferral” period for prospective donors who have returned from any of the nearly 30 countries and territories affected by the virus. The mosquito-borne pathogen, which has spread explosively through the Americas in recent months, is suspected of being linked to a birth defect.

The U.K.'s move comes a day after the America Red Cross made the same appeal, saying the temporary policy was necessary despite the “extremely low” risk of Zika being transmitted through a blood transfusion in the U.S. The group said its policy will apply to anyone who has traveled to Mexico, the Caribbean or Central or South America during the past four weeks.

“We will also ask that if a donor does donate and subsequently develops symptoms consistent with Zika virus infection within 14 days of that donation, that he or she immediately notify the Red Cross,” its vice president of scientific affairs, Susan Stramer, said in a statement. But she added that “donating blood is a safe process and people should not hesitate to give or receive blood.”

The professional standards group AABB published a lengthy set of guidelines this week in response to the ongoing Zika outbreak. It said the 28-day, self-deferral policy “should be an effective measure to reduce the risk posed by Zika virus transfusion transmission.”

Officials at the U.S. Food and Drug Administration are assessing whether travelers who have visited places with local Zika transmission should defer donating blood.

According to the Centers for Disease Control and Prevention, the Zika virus usually remains in the blood of an infected person for a few days to a week.