Study Suggests Naturally-Acquired Immunity Against Zika Virus May Already Occur

One of the most troubling aspects of Zika virus is the fact that the disease is known to cause severe, sometimes even life-threatening birth defects in infected babies. However, new research—published in PLOS Pathogens—suggests that some mothers living in particularly high-risk regions may have naturally-acquired immunity against the virus and these protective effects may continue throughout pregnancy. In addition, this immunity could be transferred to susceptible women that have not acquired immunity naturally, at least in theory.

For the study, investigators from the Cincinnati Children’s Perinatal Institute took a closer look at Zika infection in mice. Two groups of pregnant mice were infected with the virus: one group was reinfected with the virus after it was confirmed that they had cleared a previous asymptomatic infection, and one group had no previous infection.

What the researchers found was surprising—mice that were previously infected with the virus, but had not shown any symptoms, had “markedly reduced” susceptibility to the virus than those mice who were “undergoing a first infection during pregnancy,” according to a press release on the study. In addition, “Mice that didn't have prior Zika infections developed clinical symptoms and sharply increased levels of Zika virus in their blood, which spread to fetal tissues.” Most of the babies of those mice that had cleared a prior asymptomatic infection did not have Zika virus in their bodies.

The investigators posit that after having “cleared” asymptomatic infections, the mice created increased levels of immunoglobulin antibodies that then offered protection against the virus. These results suggest that human women with asymptomatic Zika infections may have the potential to naturally acquire immunity that could protect them against reinfection, too, and maybe even protect their babies in future pregnancies. In addition, the results suggest that diagnostic tests can be developed to “identify naturally immune women and distinguish them from women at high risk of infection,” according to the press release.

The investigators also found that they could transfer the neutralizing antibodies from immune mice to susceptible mice through serum transfusion. These findings suggest a potential therapeutic opportunity lies in using the antibodies. According to lead author of the study, Sing Sing Way, MD, PhD, a pediatrician in the Division of Infectious Diseases at the institute, “There are promising efforts underway to develop a vaccine against Zika, but currently there isn’t one. These results suggest that in lieu of a vaccine, Zika-fighting antibodies could be used therapeutically to help protect high-risk women.”

In fact, the investigators feel that there is also the potential for combining protective antibodies with a future vaccine, to provide an even more “synergistically robust level of protection.” However, more research is needed on the levels of antibodies that are created when humans are infected with Zika virus (not only mice) and how the antibodies work in pregnant women, according to Dr. Way.