Zika virus surveillance post‐epidemic in blood donors from São Paulo, Brazil 2016–2020

Introduction Zika virus (ZIKV) is primarily transmitted through the bite of the Aedes aegypti mosquito, though transmission via blood transfusion has also been documented. During the 2015 ZIKV epidemic in Brazil, severe complications were observed in pregnant women, leading to fetal microcephaly. This study evaluated the persistence of ZIKV in blood donated by healthy individuals during the post‐epidemic period from 2016 to 2020. Methods Blood donor samples from 109 296 individuals were screened for ZIKV RNA using nucleic acids extracted from plasma pools (six donors per pool). These samples had previously undergone routine nucleic acid testing (NAT) for HBV, HCV and HIV. Results Viral RNA (Ribonucleic Acid) was detected in a donor sample from the city of Santos in May 2016, resulting in a prevalence of 0.0009%. The positive donor was confirmed through viral sequencing using the Sanger method. Sequencing and phylogenetic analysis of an envelope gene amplicon revealed that the Zika virus RNA detected belonged to the Asian clade. This Asian lineage strain emerged in Brazil, Fortaleza, in 2015, isolated in northeastern Brazil in 2015, an area where most cases of microcephaly associated with ZIKV have been reported. A follow‐up sample collected 1 month after donation showed seroconversion. Conclusion The detection of ZIKV RNA by NAT in a donated blood sample demonstrates that, although extremely rare, the virus is still present. Periodic active surveillance of blood donations for viruses associated with past outbreaks may help identify an incipient resurgence before it develops into a new epidemic.