Preeclampsia remains one of the most dangerous and least understood complications of pregnancy. Affecting approximately 3–8% of pregnancies worldwide, it can lead to severe organ damage, premature birth, and in the most extreme cases, maternal or neonatal death. Despite decades of research, scientists still do not fully understand why preeclampsia occurs, and prevention strategies are limited. In high-risk pregnancies, low-dose aspirin is sometimes prescribed, but it does not eliminate the risk, leaving many women vulnerable.

Now, a major global study suggests that COVID-19 vaccination during pregnancy—particularly booster doses—may reduce the risk of preeclampsia, even in women who never develop COVID-19.

Understanding the Link Between COVID-19 and Preeclampsia

When the COVID-19 pandemic emerged, clinicians quickly noticed a concerning trend: pregnant women infected with SARS-CoV-2 appeared more likely to develop preeclampsia. Both conditions share underlying mechanisms, including inflammation and damage to blood vessels. COVID-19 infection can disrupt the placenta and impair blood flow, increasing the strain on the mother’s organs and potentially triggering preeclampsia.

These observations prompted researchers to ask whether preventing COVID-19 through vaccination could also reduce preeclampsia risk—and whether vaccination might provide additional protective benefits beyond preventing infection.

The INTERCOVID Study

To investigate these questions, the INTERCOVID consortium conducted a large observational study involving 6,527 pregnant women across 18 countries, recruited between March 2020 and June 2022. Participants were classified based on their COVID-19 vaccination status, and researchers tracked who contracted COVID-19 during pregnancy and who developed preeclampsia.

Using statistical models, the team adjusted for factors that influence preeclampsia risk, including maternal age, body mass index, smoking, pre-existing medical conditions, and geographic location.

Key Findings: Vaccination Lowers Preeclampsia Risk

The analysis revealed several notable findings:

  • Contracting COVID-19 during pregnancy increased the risk of preeclampsia by 45%.
  • Among unvaccinated women, the risk increase was even higher, reaching 78%.
  • Women who received booster doses of the COVID-19 vaccine had a 33% lower odds of developing preeclampsia compared to unvaccinated women.
  • In women with pre-existing health conditions such as diabetes or hypertension, the risk fell by 42%.
  • The protective effect was observed even in women who never contracted COVID-19, suggesting that vaccination may confer benefits beyond simply preventing infection.

In addition to reducing preeclampsia risk, booster vaccination was associated with broader maternal and neonatal benefits: a 32% lower risk of severe maternal complications and a 29% lower risk of severe newborn complications or death.

How Vaccines May Protect Against Preeclampsia

While COVID vaccines are primarily designed to prevent infection, they also modulate the immune system. Researchers speculate that vaccination may reduce harmful inflammation or stabilize blood vessels—both of which play a role in preeclampsia development. By preventing severe infection and supporting maternal immune health, vaccines may help maintain proper placental function and reduce vascular stress.

Dr. Jagjit S. Teji, co-author of the study and a neonatologist at Ann & Robert H. Lurie Children's Hospital the INTERCOVID consortium at the Nuffield Department of Women’s & Reproductive Health