Severity of maternal SARS-CoV-2 infection and perinatal outcomes during the Omicron variant dominant period: UK Obstetric Surveillance System national cohort study

Objectives

To describe the severity of maternal infection when the Omicron SARS-CoV-2 variant was dominant (15/12/21-14/01/22) and compare outcomes among groups with different vaccination status.

Design

Prospective cohort study

Setting

UK consultant-led maternity units

Participants

Pregnant women hospitalised with a positive SARS-CoV-2 PCR test up to 7 days prior to admission and/or during admission up to 2 days after giving birth.

Main outcome measures

Symptomatic or asymptomatic infection. Vaccination status. Severity of maternal infection (moderate or severe infection according to modified WHO criteria). Mode of birth and perinatal outcomes.

Results

Out of 1561 women admitted to hospital with SARS-CoV-2 infection, 449 (28.8%) were symptomatic. Among symptomatic women admitted, 86 (19.2%) had moderate to severe infection; 51 (11.4%) had pneumonia on imaging, 62 (14.3%) received respiratory support, and 19 (4.2%) were admitted to the intensive care unit (ICU). Three women died (0.7%). Vaccination status was known for 383 symptomatic women (85.3%) women; 249 (65.0%) were unvaccinated, 45 (11.7%) had received one vaccine dose, 76 (19.8%) had received two doses and 13 (3.4%) had received three doses. 59/249 (23.7%) unvaccinated women had moderate to severe infection, compared to 10/45 (22.2%) who had one dose, 9/76 (11.8%) who had two doses and 0/13 (0%) who had three doses. Among the 19 symptomatic women admitted to ICU, 14 (73.7%) were unvaccinated, 3 (15.8%) had received one dose, 1 (5.3%) had received two doses, 0 (0%) had received 3 doses and 1 (5.3%) had unknown vaccination status.

Conclusion

The risk of severe respiratory disease amongst unvaccinated pregnant women admitted with symptomatic SARS-CoV-2 infection during the Omicron dominance period was comparable to that observed during the period the wildtype variant was dominant. Most women with severe disease were unvaccinated. Vaccine coverage among pregnant women admitted with SARS-CoV-2 was low compared to the overall pregnancy population and very low compared to the general population. Ongoing action to prioritise and advocate for vaccine uptake in pregnancy is essential.

SUMMARY BOX

What is already known on this topic

• In non-pregnant adults, growing evidence indicates a lower risk of severe respiratory disease with the Omicron SARS-CoV-2 Variant of Concern (VOC).

• Pregnant women admitted during the periods in which the Alpha and Delta VOC were dominant were at increased risk of moderate to severe SARS-CoV-2 infection compared to the period when the original wildtype infection was dominant.

• Most women admitted to hospital with symptomatic SARS-CoV-2 infection have been unvaccinated.

What this study adds

• One in four women who had received no vaccine or a single dose had moderate to severe infection, compared with one in eight women who had received two doses and no women who had received three doses

• The proportional rate of moderate to severe infection in unvaccinated pregnant women during the Omicron dominance period is similar to the rate observed during the wildtype dominance period

• One in eight symptomatic admitted pregnant women needed respiratory support during the period when Omicron was dominant