In a collaboration involving 41 hospitals in 18 countries, a team led by researchers at the University of Oxford has demonstrated that the Omicron variant of COVID-19 puts pregnant women at greater risk of severe illness and death, and that vaccination is effective in protecting against this.
The team had previously (in 2021) showed that women and their babies were at increased risk if they had COVID-19 in pregnancy. In this study, they set out to examine the effects of COVID-19 on maternal and perinatal outcomes during the Omicron wave specifically.
The study enrolled 4,618 pregnant women from Nov 27, 2021 (the day after WHO declared omicron a variant of concern), to June 30, 2022. Each woman with confirmed COVID-19 in pregnancy was compared with two pregnant women without COVID-19. Mothers and their babies were followed up until hospital discharge. The results were published in The Lancet.
2,886 (63%) of the women had at least a single dose of any vaccine, and 2,476 (54%) had a full primary course of vaccination (some also had booster doses).
1,545 (33%) of the women had a confirmed COVID-19 diagnosis. Overall, the researchers found that these women were at increased risk of having a severely unwell baby. The risk of them being unwell or dying themselves was also increased, and was greater if they were unvaccinated.
Among the 1,732 unvaccinated women, COVID-19 infection increased the risk of severe maternal disease and death by 1.36 times. Symptomatic infection increased the risk of preterm birth by 1.33 times.
Vaccine effectiveness was estimated by adjusting for the risk profile of the mother. Effectiveness of all vaccines combined against severe complications of COVID-19 for fully vaccinated women was 48%. After a booster dose it was 76%.
Among those women who had COVID-19, vaccine effectiveness was 74%. After a booster dose, it was 91%.
Overall, women who were fully vaccinated had a reduced risk of severe symptoms from COVID-19, complications, and death.
The researchers concluded that vaccination coverage among pregnant women remains a priority even now that Omicron is the variant of concern worldwide.