Zika virus: Current status and the vaccine pipeline

Author(s):  Dr Sherilyn Houle

The Zika virus is primarily transmitted by Aedes mosquitoes (particularly Aedes aegypti), with sexual transmission and vertical transmission during pregnancy also documented.¹ Large outbreaks in the Pacific and in the Americas caused a peak of infections in 2015-2016 and led to the World Health Organization declaring it a Public Health Emergency of International Concern in February 2016 due to links with congenital abnormalities including microcephaly, intracranial calcifications, ocular abnormalities, and fetal loss, particularly from infections acquired in the first trimester.^1-3

While global incidence has declined markedly since 2017, transmission persists at low levels across many areas of the world³ and remains a concern for some travellers, particularly those who are or may become pregnant.

Currently, no vaccines or prophylactic monoclonal antibodies against Zika are available; however, various candidates, including inactivated, mRNA, viral vector, and subunit vaccines, are under development and/or early testing with favorable safety and immunogenicity profiles to date.⁴ However, progress towards pursuing or completing phase 3 efficacy studies is hampered by multiple factors, including low case counts, a high proportion of cases that are asymptomatic (estimated at up to 80%)¹ or have mild non-specific symptoms, limited surveillance,³ and additional safety considerations required for vaccines seeking an indication for use among those who are or are planning to become pregnant.⁴

While over 90 countries worldwide have documented evidence of autochthonous mosquito-borne transmission of Zika,³ as of May 2026 there are no geographic areas with an active Zika Travel Health Notice.⁵ Regardless, health professionals are advised to counsel travellers who are or may become pregnant within 3 months of travel to a country at risk of Zika transmission on its risks and the importance of mosquito bite prevention measures. Guidance on this risk assessment and counselling is available online at https://travelhealthpro.org.uk/factsheet/5/Zika-virus-evaluating-the-risk-to-individual-travellers.

References

[1].  Zika Virus: A Review of Biology, Clinical Impacts, and Coinfections.  Santana LMB, de Moura IA, Mouzinho Ramos Tanaka Y, França RFO ‐ Viruses 2025;17(5):637 [link]
[2].  Early and Long-Term Adverse Outcomes of In Utero Zika Exposure.  Venancio FA, Quilião ME, Gabeira SCO, et al ‐ Pediatrics 2025;155(2):e2024067552 [link]
[3].  A Review of the Recent Epidemiology of Zika Virus Infection.  Rabe IB, Hills SL, Haussig JM, et al ‐ Am J Trop Med Hyg 2025;112(5):1026-1035 [link]
[4].  Zika virus vaccines and monoclonal antibodies: a priority agenda for research and development.  Ostrowsky JT, Katzelnick LC, Bourne N, et al ‐ Lancet Infect Dis 2025;25(7):e402-e415 [link]
[5].  Countries & territories at risk for Zika.  Centers for Disease Control and Prevention [link]