Transmission of herpes simplex virus (HSV-1 or HSV-2) through a blood transfusion is extremely rare, to the point that researchers aren’t certain it has ever been documented. Unlike some other infections that blood banks actively screen for, herpes simplex is not considered a meaningful transfusion risk, and donated blood is not routinely tested for it.
Why Herpes Simplex Rarely Spreads Through Blood
Herpes simplex viruses spread primarily through direct contact with skin or mucous membranes, not through the bloodstream. After an initial infection, the virus retreats into nerve cells and stays dormant there. It doesn’t persist in blood cells or circulate freely in plasma the way some other viruses do. While brief periods of viremia (virus in the blood) can occur during a primary outbreak, the amount of virus present in donated blood from someone with a latent infection is negligible.
This is a key distinction from other members of the herpesvirus family. Cytomegalovirus (CMV), for example, hides inside white blood cells and is the most significant herpesvirus transmitted through transfusion. Epstein-Barr virus and human herpesviruses 6 and 7 can also spread this way. But herpes simplex and varicella-zoster virus (the chickenpox virus) are, as one major review put it, “extremely rare events” in transfusion transmission, “if occurring at all.”
How Blood Processing Adds Protection
Modern blood banking includes a step called leukoreduction, which removes the vast majority of white blood cells from donated blood before it’s stored. Since several herpesviruses ride inside white blood cells, this process significantly reduces the chance of transmitting cell-associated viruses. The FDA recognizes leukoreduction as effective for reducing CMV transmission to high-risk patients and notes that the protection likely extends to other pathogens that live inside white blood cells.
Even for CMV, which poses a real transfusion risk, leukoreduction has been highly effective. For herpes simplex, which barely circulates in blood to begin with, the additional removal of white blood cells makes an already negligible risk even smaller.
Blood Donation Rules for People With Herpes
Having herpes does not permanently disqualify you from donating blood. According to the NIH Clinical Center’s blood donation guidelines, you cannot donate when herpes lesions or cold sores are active. Once the lesions are dry and nearly healed, donation is permitted. This policy reflects the understanding that a person with latent herpes poses no meaningful risk to transfusion recipients.
Blood banks do not screen donated units for herpes simplex antibodies or viral DNA. The mandatory screening panel for donated blood targets infections like HIV, hepatitis B, hepatitis C, syphilis, and a handful of other pathogens that are known to spread efficiently through blood products. Herpes simplex doesn’t meet that threshold.
Other Herpesviruses Are a Bigger Concern
If you’re worried about herpesvirus transmission from transfusion more broadly, the real concern is CMV, not herpes simplex. CMV is common: roughly half of adults carry it. For most healthy people, a CMV infection causes no noticeable illness. But for certain vulnerable patients, including premature infants, organ transplant recipients, and people undergoing chemotherapy, transfusion-transmitted CMV can cause serious disease. That’s why these patients often receive leukoreduced or CMV-negative blood products as an added precaution.
Human herpesvirus 8 (HHV-8), which is linked to Kaposi’s sarcoma, has shown some evidence of transfusion transmission in regions where the virus is highly prevalent. A prospective study in Uganda found a small increase in HHV-8 infection risk (roughly 2.8% per unit transfused) among children who received blood from HHV-8 positive donors. This risk was tied to the combination of high donor prevalence and the severely immunocompromised state of many recipients in that setting. In countries with low HHV-8 prevalence, this is not a practical concern.
Who Might Face Higher Risk
For a healthy adult receiving a blood transfusion in a country with modern blood banking, the risk of getting herpes simplex from that transfusion is essentially zero. The people who face any elevated risk from transfusion-transmitted herpesviruses are those with weakened immune systems: transplant patients on immunosuppressive drugs, people receiving chemotherapy, newborns (especially premature infants), and individuals with advanced HIV. Even in these groups, the concern centers on CMV rather than herpes simplex, and specific precautions are already standard practice for their transfusions.
If you’re scheduled for a transfusion and have concerns about infection risk, the safeguards built into modern blood banking, from donor screening questionnaires to leukoreduction to mandatory pathogen testing, make the overall risk of acquiring any infection from a transfusion very low. Herpes simplex, specifically, sits at the bottom of that already short list.