No 40/41a - 2024

Imported Case of Zika Virus Infection in Pregnant Woman After Travel to Thailand

Status on the Prevalence of Zika Virus

Zika virus spread epidemically in large parts of the world in 2015-17, but the prevalence has since fallen to a generally low endemic level. However, surveillance of Zika virus is inadequate in many countries and therefore, there is often no data to say more precisely how high the risk is in a specific area, making risk assessment and counseling difficult. Zika epidemiology update - May 2024.

In Thailand, however, there have been signs of increased prevalence, with a 300% increase in locally reported cases in 2023 compared to 2022, as reported in EPI-NEWS 4/2024. Cases of Zika virus have been reported from many different areas in Thailand in recent years.

Zika Virus Transmission and Symptoms

Zika virus is mainly transmitted by mosquito bites (specifically the species Aedes aegypti, also known as the yellow fever mosquito, and Aedes albopictus, known as the tiger mosquito), but can also be transmitted sexually via semen. Infection often causes only mild or no symptoms, but can be serious for pregnant women, as the virus can be transmitted to the fetus and cause severe neurological damage and malformations, including microcephaly (small head circumference due to lack of brain development or destruction of brain tissue). Although some studies show that there is a higher risk of developing microcephaly if the pregnant woman has had symptoms, there have also been cases among pregnant women who have not had symptoms.

Recent Case in Denmark of Imported Zika Virus Infection in a Pregnant Woman After Travel to Thailand

A recent case of Zika virus infection has been reported in a Danish pregnant traveler who, early in her pregnancy (weeks 8-10), stayed in Phuket province in Thailand during March-April 2024, including in Phuket city and several popular tourist destinations around the island of Phuket. During the trip, the woman experienced a few days of mild symptoms in the form of nausea, loss of appetite, and fatigue, followed by a discreet rash on her arms, legs, and torso.

The pregnant woman received a routine ultrasound scan in weeks 12 and 20 of her pregnancy, where normal conditions were found during the scanning of the fetus’s organs and growth measurements, including normal head circumference. During a growth scan of the fetus in week 26 of pregnancy taken for other reasons, a head circumference significantly below the normal range was found. MRI confirmed microcephaly and severe brain malformations. In a blood sample from the pregnant woman, IgG antibodies against Zika virus were subsequently detected. A blood sample taken earlier in pregnancy, a few days after returning from Thailand in week 10 of pregnancy (the “double test” ), was then analyzed for Zika virus and showed significantly elevated IgM and IgG antibodies against Zika virus at that time. Additionally, a tissue sample from the child was positive for Zika virus by PCR diagnostics. The diagnosis was therefore microcephaly in the fetus due to Zika virus infection.

Advice on Preventing Zika Virus in Travelers

It is important that women who are pregnant, or couples planning pregnancy, are informed about the risk of infection when traveling to areas with Zika virus prevalence: Pregnant women should be aware of the risk of Zika virus when traveling abroad (in Danish).

Specifically, there is potentially still an increased risk of Zika virus infection in Thailand, including popular tourist areas in Phuket. Therefore, SSI recommends that women who are already pregnant, and couples currently planning pregnancy, strongly consider postponing non-essential travel to Thailand.

It is also important to emphasize that there may also be a similar, but unknown, risk when traveling to other destinations in Asia, Africa, and Central and South America, corresponding to the areas where Zika virus is currently or has previously been detected. Therefore, the same recommendations apply to all these countries, see SSI’s recommendations on protecting the pregnant traveler (in Danish).

Women who have traveled to areas where Zika virus is endemic are advised to wait until 2 months after returning home before becoming pregnant. Since Zika virus can be transmitted sexually via semen, men who have stayed in a Zika risk area should use condoms for the first 3 months after returning home, and throughout the rest of the pregnancy if the woman is pregnant.

The primary prevention of Zika virus consists of mosquito bite prophylaxis. It is important to inform travelers that Aedes mosquitoes bite both during the day and at night, so the use of mosquito bite prophylaxis around the clock is necessary. There is still no vaccine (In Danish). Insect-borne viral diseases.

(P. Sandager, L. Laursen, Obstetrics and Gynecology, Aarhus University Hospital, I.M Rubin, R. Datcu, U. Schneider, Virus & Microbiological Special Diagnostics, L.S. Vestergaard, P.H. Andersen,

Department of Infectious Disease Epidemiology and Prevention)

Vaccination Against RSV (Respiratory Syncytial Virus) for People Over 60 and Pregnant Women

The Department of Infectious Disease Epidemiology and Prevention at the Statens Serum Institut (SSI) is currently receiving many inquiries about vaccination against RSV.

SSI has described the RSV vaccines in EPI-NEWS 40/2023 and 44a/2023.

The vaccines are not part of any vaccination program and must therefore be paid for by the vaccinated individual. Conditional subsidies have been granted for Arexvy^® for citizens aged 60 and over with COPD. Read more here .

If there is a medical indication for vaccination, both Abrysvo^® and Arexvy^® can be given at any interval with the seasonal vaccines against COVID-19 and influenza, EPI-NEWS 39/2024.

Health authorities in Denmark, like in many other countries, are currently evaluating the potential use of the vaccines in a vaccination program, including which groups should be offered vaccination. Until recommendations for the use of the vaccines in a vaccination program are available, self-paid vaccination can occur within the approved indication area for the vaccines.

About the Vaccines

The vaccines Abrysvo^® and Arexvy^® are approved by the European Medicines Agency (EMA) for protection against RSV disease in the lower respiratory tract in people aged 60 and over.

Additionally, Abrysvo^® is approved for use in pregnant women, who are vaccinated between weeks 24 and 36 of pregnancy. This provides passive protection against lower respiratory tract disease caused by RSV in infants from birth to 6 months of age.

For more information about the vaccines Abrysvo^® and Arexvy^®, see SSI’s vaccine lexicon.

(Department of Infectious Disease Epidemiology and Prevention)