Vaccine effectiveness against mild and severe covid-19 in pregnant individuals and their infants in England: test negative case-control study.

Summary

A national test-negative case-control study in England found high COVID-19 vaccine effectiveness in pregnant individuals, with boosters sustaining protection up to 15 weeks. Maternal vaccination, especially in the third trimester, conferred substantial protection to infants up to 6 months against symptomatic infection and hospitalisation for both delta and omicron variants.

Key Findings

• Booster vaccination yielded peak vaccine effectiveness against symptomatic disease of 98.4% (delta) and 80.1% (omicron) in pregnant individuals.
• Two-dose primary series achieved 92.7% effectiveness against hospital admission for delta in pregnancy.
• Maternal vaccination in the third trimester protected infants up to 6 months: effectiveness against symptomatic disease 86.5% (delta) and 56.6% (omicron), and against hospital admission 94.7% (delta) and 78.7% (omicron).
• Protection did not wane up to 15 weeks post-booster in pregnant individuals.

Clinical Implications

Prioritise primary and booster COVID-19 vaccination during pregnancy—particularly in the third trimester—to protect both the mother and the infant up to 6 months of age.

Limitations

• Test-negative design may be affected by healthcare-seeking behavior and residual confounding
• Effectiveness beyond 15 weeks post-booster and for later omicron sublineages was not assessed

Future Directions

Assess durability of maternal and infant protection across emerging variants and evaluate optimal timing of boosters in different trimesters.