COVID-19 Booster Vaccination Linked to 33% Lower Preeclampsia Risk in Pregnant Women, International Study Finds

A large international study published in eClinicalMedicine found that COVID-19 vaccination, particularly with a booster dose, was associated with a significantly lower risk of developing preeclampsia in pregnant women. The research, which followed more than 6,500 pregnant women across 18 countries, offers evidence that maternal vaccination may protect against one of the most serious pregnancy complications.

The study enrolled 6,527 pregnant women from 40 hospitals between 2020 and 2022. Pregnant women with a documented COVID diagnosis were matched to a control without COVID in the same hospital. Of the 2,774 vaccinated women included in the analysis, 1,795 (64%) received mRNA vaccines, and 848 (31%) also received a booster dose. Of those who got a booster, 67% received it with an mRNA vaccine.

Researchers found that contracting COVID-19 during pregnancy increased the risk of preeclampsia by 45% overall. Among the unvaccinated, that risk jumped to 78%. Vaccination, however, was tied to a 33% lower odds of preeclampsia among those who received a booster dose. For mothers with pre-existing conditions such as diabetes or chronic high blood pressure, the booster dose was associated with a reduced preeclampsia risk of 58%.

A co-author from a neonatology division said the results support the importance of strengthening COVID vaccination programs during pregnancy, emphasizing boosters and ensuring that pregnant people across the world have equitable access to the vaccine. The principal investigator of the study, based at the Oxford Maternal & Perinatal Health Institute, noted that the evidence suggests maternal vaccination may influence pathways involved in preeclampsia development, indicating a broader immunological or vascular benefit of vaccination.

Beyond blood pressure complications, the study found that vaccinated women were also less likely to experience preterm births or severe complications during delivery. Researchers suggest the vaccine may train the immune system to handle inflammation more effectively, helping the placenta and blood vessels remain healthy throughout pregnancy.

Preeclampsia affects roughly 3% to 8% of pregnancies globally. While its exact cause is not fully understood, it involves inflammation and issues with blood vessel function — the same biological pathways affected by COVID-19.

A separate review article published in Frontiers examined vaccination strategies for pregnant women using second-generation COVID-19 vaccines, which include Omicron-containing bivalent vaccines and later updated formulations such as those based on XBB.1.5 and JN.1 lineages. The review highlighted that pregnant women undergo physiological immune modulation during pregnancy, increasing their susceptibility to severe disease following SARS-CoV-2 infection, with elevated rates of intensive care unit admission and increased maternal mortality. Additional pregnancy-related changes — including heightened oxygen consumption and reduced respiratory reserve — further compromise respiratory function in infected individuals.

The review also noted that vaccine hesitancy remains prevalent among pregnant women due to concerns about potential adverse effects and fetal safety, underscoring the need for further research to refine vaccination protocols and support equitable access.