Covid-19 vaccination during pregnancy helps protect infants from infection through their first six months of life, but it may be less effective against newer covid-19 variants.
at Kaiser Permanente in California and his colleagues examined the effectiveness of vaccination during pregnancy against covid-19 in 30,311 infants who were born between 15 December 2020 and 31 May 2022 at 20 health centres in northern California. Of the infants, 19,418 had unvaccinated mothers, 9755 had mothers who received two or more covid-19 vaccine doses during pregnancy and 1138 had mothers who received only one covid-19 vaccine dose while pregnant.
Using medical records, the researchers found that 940 infants tested positive for covid-19 by 6 months old. They then grouped test results based on which covid-19 variant 鈥� delta or omicron 鈥� was predominantly circulating at the time.
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They found that during the period when delta was dominant, two or more vaccine doses in pregnancy reduced the risk of an infant testing positive for covid-19 by 84 per cent during the first two months of life. By 6 months old, this protective effect fell to 56 per cent. Meanwhile, during the period when omicron was predominant, two or more covid-19 vaccine doses in pregnancy reduced the risk of a positive covid test by 21 per cent during the first two months of life and 13 per cent during the first six months of life. These results were consistent even after adjusting for factors such as age, race and socioeconomic status.
Taken together, these findings indicate that vaccination during pregnancy protects infants from covid-19, but that protection wanes over time and may be less effective against newer variants.
However, when Zerbo and his team ran a subsequent analysis on infants born to mothers who received one covid-19 vaccine before pregnancy and two during pregnancy, they found that, during the omicron period, infants had an 89 per cent lower risk of testing positive in their first two months of life. By 6 months old, they had a 48 per cent lower risk. This suggests that an extra covid-19 dose in pregnancy could improve protection for infants against omicron.
鈥淐hildren who are less than 6 months of age are not eligible to get vaccinated against covid,鈥� says Zerbo. 鈥淪o, this research is showing that vaccination during pregnancy will provide them with protection until they鈥檙e old enough to get their own vaccine.鈥�
Nature Communications
