Zika did not vanish after the 2015 to 2016 epidemic. It quieted, became endemic in the same regions where dengue and chikungunya circulate, and dropped out of headlines. The teratogenic risk is still real. The sexual transmission window is still real. And the geographic risk surface is wider now than before the outbreak that put Zika on the map. CDC and WHO both maintain active travel guidance, but the public conversation moved on years ago.
For most travelers, Zika is a low-grade infection that produces a mild rash, joint pain, and red eyes for a week. For people who are pregnant, trying to conceive, or partnered with someone who is, the calculation is different. Congenital Zika syndrome causes microcephaly, brain malformations, eye abnormalities, hearing loss, and limb contractures. There is still no licensed vaccine. This post is part of outbreak-aware travel, aimed at the pregnancy-related decisions that are not getting the attention they should.
Key Takeaways
- Zika is still circulating year-round in much of Latin America, the Caribbean, parts of Southeast Asia, and parts of sub-Saharan Africa. The 2015 to 2016 epidemic ended; the endemic baseline did not.
- The teratogenic risk window is the entire pregnancy. First-trimester infection has the highest risk of microcephaly and severe neurological malformation; later infection still produces fetal damage.
- Zika is transmitted sexually for at least 3 months after a male partner's infection. Couples planning pregnancy after travel must wait 3 months (male partner) or 2 months (female partner or unknown exposure) before trying.
- About 80 percent of Zika infections are asymptomatic, so symptom-based travel screening misses most exposures. CDC recommends counseling based on travel history, not symptoms.
- No licensed Zika vaccine yet. Multiple candidates are in Phase II trials. The most promising have used mRNA platforms similar to COVID-19 vaccines.
Where is Zika circulating now?
Zika is endemic across most of the geographic range it reached during the 2015 to 2016 epidemic. CDC's current Zika travel notice list includes most of the Americas (Mexico, Central America, the Caribbean, and most of South America), parts of Southeast Asia (Philippines, Thailand, Vietnam, Indonesia, Malaysia, Cambodia, Laos), parts of Oceania (Pacific island nations), and parts of sub-Saharan Africa.
The risk pattern shifted from outbreak-with-a-peak to seasonal endemic baseline with periodic local clusters. Surveillance is uneven: many countries no longer test routinely for Zika unless a pregnant patient or a microcephaly case prompts it. CDC maintains a tiered map (Areas with Risk of Zika, Areas with Mosquitoes that can Spread Zika but No Reports, Areas with Low Likelihood) that travelers should check before booking, especially for pregnancy-related itineraries.
Why is pregnancy the central Zika risk?
Zika crosses the placenta and infects fetal neural progenitor cells, the cells that build the developing brain. Infection during pregnancy can cause congenital Zika syndrome, which includes severe microcephaly, intracranial calcifications, eye abnormalities (including chorioretinal atrophy), congenital contractures, and early hypertonia. Less severe cases produce developmental delays and seizures that may not be apparent at birth.
The risk by trimester (estimates from the Brazilian and US Zika cohorts):
| Timing of infection | Estimated risk of birth defects |
|---|---|
| First trimester | 8 to 15 percent |
| Second trimester | 3 to 8 percent |
| Third trimester | 1 to 5 percent |
| Periconception (4 weeks before LMP through implantation) | Possible but less defined |
These are population estimates. Individual risk depends on viral load, gestational age at infection, and likely host factors that are not yet well characterized. Asymptomatic Zika infection in pregnancy carries the same teratogenic risk as symptomatic infection, which is the part most travel counseling underweights.
How does Zika spread sexually?
Zika persists in semen substantially longer than in blood. Median time to clearance in semen is about 30 days in most studies, but virus has been detected by RT-PCR up to 6 months after symptom onset in a small percentage of men. CDC's current guidance, which is more conservative than typical viral kinetics, sets the male-partner sexual transmission window at 3 months after exposure or symptom onset.
Practical guidance for couples after travel to a Zika-risk area:
- Male partner traveled, planning pregnancy: wait 3 months from return (or symptom onset) before trying to conceive
- Female partner traveled, planning pregnancy: wait 2 months from return (or symptom onset) before trying to conceive
- Both partners traveled: take the longer interval (3 months from male partner's return)
- Already pregnant, partner traveled to Zika-risk area: use condoms or abstain for the duration of pregnancy
These intervals are conservative because the consequence of a missed window is congenital Zika syndrome. The same logic applies to fertility treatment timing: most reproductive medicine clinics ask travel histories and may delay procedures based on these windows.
What are the symptoms of Zika?
About 80 percent of Zika infections are asymptomatic. Among the 20 percent that are symptomatic, illness is typically mild: low-grade fever, maculopapular rash (often itchy), arthralgia (especially small joints), conjunctivitis (non-purulent), headache, and myalgia. Symptoms last 2 to 7 days and resolve without treatment. Severe Zika in adults is uncommon.
Two complications are documented in adults. Guillain-Barré syndrome, a postinfectious ascending paralysis, follows roughly 0.02 percent of Zika infections in epidemic settings, similar to the rate after some other viral infections. Encephalitis and myelitis have been reported rarely. Diagnosis is by RT-PCR on serum or urine in the first 14 days of illness, then by IgM serology with confirmatory neutralization testing for distinguishing Zika from cross-reactive flaviviruses (dengue, yellow fever).
How should you plan travel around pregnancy?
CDC and ACOG advise pregnant people to avoid all non-essential travel to areas with Zika risk for the duration of pregnancy. For couples planning to conceive, the recommendation is to delay attempts until after the post-travel window described above. Discussions with a travel medicine clinician or obstetrician are useful for borderline situations: occupational travel, family obligations, low-risk areas with limited recent surveillance.
If travel cannot be avoided, mosquito-borne disease prevention takes on much higher stakes than usual: EPA-registered repellent (DEET 20 to 30 percent, picaridin 20 percent, IR3535, or oil of lemon eucalyptus for non-pregnant) on all exposed skin, permethrin-treated clothing, air conditioning or screened accommodations, and consistent condom use during the trip and for the post-trip transmission window. The Aedes aegypti mosquito that transmits Zika is most active during the day, especially early morning and late afternoon, which differs from malaria mosquitoes.
Why is there still no Zika vaccine?
Multiple candidates have entered clinical trials, including DNA-based, inactivated whole-virus, mRNA, and viral-vector platforms. The challenge has been epidemiology: as the 2015 to 2016 epidemic ended, transmission dropped below the threshold needed for efficient Phase III efficacy trials. Without enough field cases, you cannot show clinical efficacy in the standard way.
Two strategies have emerged. Controlled human infection model trials, which deliberately infect volunteers with a weakened challenge strain in a contained setting, are under serious consideration and have run for other flaviviruses. And immunological correlates of protection that allow inferred efficacy from antibody titers, similar to the path used for some COVID-19 boosters, are being developed. A licensed Zika vaccine before the next outbreak is plausible but not certain.
FAQ
Is Zika still being reported anywhere?
Yes. CDC's ArboNET and PAHO's regional surveillance both continue to receive Zika case reports, primarily from Brazil, Colombia, Bolivia, Mexico, India, and parts of Southeast Asia. Reporting is incomplete because routine Zika testing has dropped substantially since 2017. Local transmission also continues sporadically in Florida and Texas, with rare imported-then-local clusters.
How long does Zika immunity last?
Long-term, probably for life, based on what we know about closely related flaviviruses. Reinfection has not been clearly documented in immunocompetent adults. The complication is cross-reactivity: prior dengue infection produces antibodies that bind Zika and complicate serological diagnosis, though they do not appear to provide clinical protection against Zika.
Can men get Zika from a female partner?
Documented but rare. Female-to-male sexual transmission has been reported once in the literature; the standard sexual transmission concern is male-to-female and male-to-male, where seminal viral persistence is the main mechanism. CDC guidance focuses on the conservative male-partner intervals because the data are clearer.
Should I get tested for Zika after returning from a risk area?
Routine testing of asymptomatic, non-pregnant travelers is not recommended; the test characteristics make false positives more likely than meaningful true positives. Testing is recommended for symptomatic travelers, pregnant travelers regardless of symptoms, and the partners of pregnant travelers in some scenarios. Talk to a travel medicine or obstetric clinician for individualized advice.
How is Zika different from dengue?
Both are mosquito-borne flaviviruses transmitted by Aedes aegypti, both produce mild flu-like illness with rash. Zika has lower acute morbidity than dengue but causes congenital disease, which dengue does not. Dengue can cause hemorrhagic disease, particularly on second infection; Zika rarely does. The two often co-circulate in the same regions, which complicates diagnosis without specific testing.