COVID-19 vaccination during pregnancy protects babies against SARS-CoV-2 infection during their first 4 months of life, according to a study published yesterday in JAMA internal medicine.
In the cohort study, which included all infants born in Norway late last year and early this year, the incidence of COVID-19 was lower in babies born to women who received the vaccine. Moderna or Pfizer-BioNTech during the second or third trimester of pregnancy.
Protection, however, was more than twice as high during the Delta variant-dominated period than during the Omicron period.
Infant protection 33% during Omicron
The researchers, primarily from the Norwegian Institute of Public Health, note that studies have shown that babies born to women vaccinated during pregnancy are protected against diseases like whooping cough (whooping cough) and influenza. So they set out to assess whether the phenomenon was true for COVID vaccines.
They note that, of 21,643 Norwegian babies born from September 2021 to February 2022, 9,739 of them (45.0%) were born to women who received a second or third dose of a COVID-19 mRNA vaccine. 19 during pregnancy.
Investigators analyzed data on polymerase chain reaction (PCR) test results for mothers and their babies, all of which are registered in the Norwegian Communicable Disease Surveillance System. They included data on the first positive SARS-CoV-2 PCR test for babies at least 1 day after birth up to 4 months of age, as well as information on women who tested positive 14 days. or more before delivery. In Norway, free PCR tests are widely available.
The incidence rate of a positive COVID-19 test for infants 0-4 months overall was 5.8 per 10,000 days of follow-up. For babies born to women vaccinated during the Delta period, it was 1.2 per 10,000 days of follow-up, versus 3.0 for babies born to unvaccinated mothers, for a vaccine efficacy of 71% (hazard ratio adjusted [aHR], 0.29; 95% confidence interval [CI]0.19 to 0.46).
During the Omicron period, however, the incidence rate was 7.0 per 10,000 follow-up days in the vaccinated mother group, compared to 10.9 per 10,000 follow-up days in the unvaccinated group. This translates to a vaccine efficacy in neonates of 33% (aHR, 0.67; 95% CI, 0.57 to 0.79).
Compared to vaccinated mothers, unvaccinated mothers were younger and had more children and less education, and a lower proportion of them were born in Scandinavia. The percentage of infants born to vaccinated mothers increased over the study period. Most newborns with a positive COVID-19 test in fall 2021 were born to unvaccinated mothers, but an infant’s age at the time of a positive test was similar between the groups.
The infant hospitalization rate for COVID-19 as the primary diagnosis was 0.07% in both groups.
Strengths, limitations of the study
The authors say the strengths of the study include the breadth and depth of Norwegian population data, which is possible due to mandatory reporting in the country. They write: “We believe that the results of our study are generalizable to other pregnant populations. This hypothesis is reinforced by the fact that the results align with the results of the United States study examining maternal vaccination against COVID- 19 and the risk of infant hospitalization for COVID-19.”
Limitations include lack of testing for variants, possible antibody protection provided by breastfeeding, potential healthy vaccinee bias, varied follow-up times, and lack of information about infant disease symptoms. However, they did not call any of the limitations major.
The authors conclude: “The results of this study provide early evidence suggesting that infants experience passive protection against SARS-CoV-2 infection following maternal COVID-19 vaccination during pregnancy.
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