COVID-19 vaccine during pregnancy may protect infants

COVID-19 vaccination during pregnancy protects babies from SARS-CoV-2 infection in their first 4 months of life, according to a study published yesterday JAMA Internal Medicine

In the cohort study, which included all babies 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 Moderna or Pfizer-BioNTech vaccine during the second or third trimesters. of the pregnancy.

However, protection was more than twice as high during the period dominated by the Delta variant as during the Omicron period.

Protection for infants 33% during Omicron

The researchers – mainly from the Norwegian Institute of Public Health – note that studies have shown that babies born to women who are vaccinated during pregnancy are protected against diseases such as whooping cough (whooping cough) and flu. So they wanted to assess whether the phenomenon applied to COVID vaccines.

They note that of the 21,643 Norwegian babies born between September 2021 and February 2022, 9,739 of them (45.0%) were born to women who received a second or third dose of an mRNA COVID-19 vaccine during pregnancy. got.

The researchers 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 include data on the first SARS-CoV-2 positive PCR test for infants at least 1 day after birth to 4 months of age, as well as information on women who had a positive test 14 or more days before delivery. Free PCR tests are widely available in Norway.

The incidence of a positive COVID-19 test for infants aged 0-4 months was a total of 5.8 per 10,000 follow-up days. For babies born to vaccinated women during the Delta period, it was 1.2 per 10,000 follow-up days, versus 3.0 for babies born to unvaccinated mothers, for a vaccine efficacy of 71% (adjusted hazard ratio [aHR], 0.29; 95% confidence interval [CI]0.19 to 0.46).

However, in the Omicron period, the incidence was 7.0 per 10,000 follow-up days in the mother vaccinated group, compared to 10.9 per 10,000 follow-up days in the unvaccinated group. This translates into 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 percentage of them were born in Scandinavia. The percentage of infants born to vaccinated mothers increased during the study period. Most newborns with a positive COVID-19 test in the fall of 2021 were born to unvaccinated mothers, but a baby’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 study’s strengths are the breadth and depth of Norway’s population data, which is possible due to mandatory reporting in the country. They write: “We believe that our study results are generalizable to other pregnant populations. This assumption is reinforced by the fact that the findings are consistent with the results of the US study of maternal COVID-19 vaccination and the risk of infant hospitalization.” for COVID-19.”

Limitations include the lack of testing for variants, the potential antibody protection afforded by breastfeeding, potential bias of healthy vaccinees, different follow-up times, and a lack of information about the infants’ symptoms of disease. However, they did not characterize any of the limitations as important.

The authors conclude: “The findings of this study provide early evidence to suggest that infants benefit from passive protection against SARS-CoV-2 infection following maternal COVID-19 vaccination during pregnancy.”

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