Zika burst onto the world stage in 2015, the only known mosquito-borne virus that can cause severe birth defects. By the height of the epidemic the following year, when more than 200,000 people had been infected and some 3,000 babies experienced birth defects in Brazil, US health officials issued a first-of-its-kind travel advisory. Women of childbearing age, whether they were pregnant or wanted to be soon, were told not to travel to 68 countries where Zika had been circulating.
Flights were canceled, itineraries changed, and the tourism industries in the affected places were hit hard.
Three years on, the epidemic has mostly died down (except in northwest India), and the travel warnings are finally beginning to relax.
On March 14, the Centers for Disease Control and Prevention eased its travel advisory, suggesting pregnant women avoid countries with active Zika while anyone planning a pregnancy should talk to their doctor. The World Health Organization is coming out soon with a similar travel advisory, as the Washington Post first reported this week.
There’s just one problem with this new advice: It’s vague, and is likely going to lead to some confusion for people planning trips abroad.
So where does that leave women and their partners who are pregnant or want to conceive? Let’s break it down.
Where Zika’s been, and where it may be going
First, some Zika basics. The virus was first discovered in 1947 (in the Zika forest in Uganda), and until recently, it seemed to barely bother humans — until 2015, when it suddenly began spreading fast.
The virus had arrived in Brazil, where the conditions for an epidemic were ripe: lots of Aedes aegypti mosquitoes, a vector for the virus; lots of people living right next to the mosquitoes; and a population that had no immunity to Zika. By 2016, the WHO declared the outbreak a public health emergency. By 2017, hundreds of thousands of people had been infected throughout South and Central America, as well as in parts of Africa and Asia.
With all those cases, scientists learned new facts about Zika. Most people don’t develop any symptoms after being infected. And for everyone else, the symptoms are usually mild — a rash, headaches, pain in the joints and bones, and fever. They show up between three and 12 days after the initial mosquito bite and resolve within a week. (Hospitalization is uncommon, and death is rare.)
Most importantly, though, scientists have found evidence that Zika causes severe birth defects, most notably microcephaly. The congenital condition is associated with a small head and incomplete brain development, part of a pattern of Zika-linked birth defects, including eye damage and muscle problems. Zika is also linked to Guillain-Barré syndrome, a neurological condition that can lead to paralysis.
Zika researchers learned more about how Zika is spread. While the virus is passed mainly through mosquitoes, people can catch it through sexual intercourse, which is why there’s Zika concern for men too. The male partners of pregnant women and women who want to become pregnant are advised to use condoms or avoid sex for the duration of a pregnancy or three months before conceiving if they’ve traveled to areas with current or past Zika.
Aside from scientific discovery, there was one other upside to this epidemic: Researchers believe the virus spread so extensively that it’s not circulating widely anymore. People who get Zika develop immunity to the virus, so they can’t be reinfected. That means new epidemics in places that were hit hard by the virus have “burned themselves out,” said Yale University infectious diseases expert Albert Ko.
But Zika hasn’t disappeared entirely. Northwestern India is currently experiencing a Zika outbreak, and researchers suspect the virus may be spreading more broadly in South and Southeast Asia, but they aren’t sure both because of spotty disease surveillance systems and because smaller outbreaks are likely to go unnoticed. (Remember, for most people, Zika causes no symptoms.)
Ko noted that even within countries or regions in the Americas that had thousands of cases in the past few years, there are some pockets that didn’t see widespread transmission at the height of the epidemic. These areas could be affected now. For example, there was a Zika epidemic in Cuba in 2017 after the virus died down in the rest of the Caribbean. “That makes us worry that there may still be some transmission” in places that have A. aegypti mosquitoes, said Ko, even if they’ve experienced Zika before.
So where does that leave women who are pregnant or want to be soon?
One of the big challenges around helping women make informed choices about Zika risk is that we don’t know exactly where it’s spreading. Again, disease surveillance systems are “limited in many areas of the world,” a WHO spokesperson said. So health authorities’ ability to tell whether Zika is still circulating, especially at low levels, is hard. And that means that just because Zika isn’t popping up on epidemiological maps in a country doesn’t mean it’s not there.
What’s more, since “many doctors just don’t keep up with Zika,” it’ll be hard for them to guide women in navigating the risks, said Ko.
Ultimately, the decision of whether to travel to a place where there’s a possibility of Zika infection depends on the individual’s tolerance of risk. For pregnant women, it makes sense to avoid traveling to areas with known active Zika outbreaks, such as northwest India, right now, CDC suggests.
In other areas where there’s been past Zika transmission, health officials can’t say for sure that Zika isn’t spreading now, even if it’s unlikely and they don’t have evidence that it’s currently being transmitted. In those cases, pregnant women will need to decide about whether they want to take a chance, however remote. “Talk to a health care provider,” the CDC advises.
For women who are planning a pregnancy and want to travel to a place with past or current Zika, the gray zone gets bigger. Those who have a low risk tolerance might just avoid travel, said Ko. For women who need or want to travel, health officials advise waiting two months until after the trip to become pregnant.
For men with a pregnant partner, wearing condoms or avoiding sex during the pregnancy makes sense. And for men with a partner who would like to become pregnant, the CDC suggests waiting at least three months after your trip to conceive so that the virus (if it was transmitted) has been cleared from the body.
The CDC also has a helpful list of countries with current or past transmission, as well as a map of where Zika-carrying mosquitoes live. The agency also advises taking precautions to avoid mosquito bites, like wearing repellent and long sleeves.
“What I tell my patients,” said Ko, “is if you’re a woman of childbearing age and you’re planning a family and you don’t want any risk, it’s good to postpone your trip.”
For women who want kids in the near future, Ko said, “It’s reasonable to go [because] the risk of transmission is extremely low. And while we cannot say for sure there’s no transmission, it’s likely to be low, so in those situations, one obvious way to mitigate risk is to postpone conception.” For everyone else, there’s (relatively) good news. The vast majority of people who contract Zika will never know they had it.