Findings suggest vaccination during pregnancy may have benefits for both mother and baby
Two doses of the mRNA Covid-19 vaccine during pregnancy are highly effective against Delta infection and moderately effective against Omicron infection, and are linked to a lower risk of hospital admission in babies under six months, according to a published Canadian study today by The BMJ.
Protection against Omicron infection was greatest when the mother received a second dose of vaccine late in pregnancy and was also greatest for babies in their first eight weeks of life. Receiving a third (booster) dose during pregnancy also strengthened protection against Omicron.
Although most cases of Covid-19 in infants are mild, rates of hospitalization and severe illness have been higher in infants compared to older children, especially during the first month of life or when infection is complicated by other conditions. .
Covid vaccines are not yet authorized for babies under six months, but emerging evidence suggests that vaccination during pregnancy can reduce the risk of infection and hospitalization in babies, as antibodies are transferred across the placenta and breast milk (a process known as passive immunity).
To shed more light on this, researchers in Canada set out to estimate the effectiveness of maternal Covid-19 mRNA vaccination during pregnancy against Delta and Omicron infection and hospitalization in infants.
The study involved babies under six months old who were born in Ontario between May 7, 2021 and March 31, 2022 and who received a PCR test for Covid-19 infection between May 7, 2022. 2021 and September 5, 2022.
This information was then linked to data on the mother’s mRNA Covid-19 vaccination during pregnancy (one, two or three doses) or unvaccinated (no dose), and to recorded hospital admissions related to Delta and Omicron in babies.
A variety of potentially influential factors were taken into account, including the mother’s age at the time of delivery, the number of previous pregnancies, pre-pregnancy conditions such as diabetes, heart disease and asthma, and the sex of the baby.
In total, 8809 infants were included in the main analysis (99 Delta-positive cases compared to 4365 negative controls and 1501 Omicron cases compared to 4847 controls).
The results show that two doses of vaccine during pregnancy were 95% effective against Delta infection in infants and 97% effective against childhood Delta hospitalization.
The efficacy of two doses against Omicron infection in infants (45%) and hospital admission (53%) was moderate, but improved with a third dose during pregnancy (73% and 80%, respectively).
The efficacy of two doses against Omicron infection was greatest when the second dose was administered in the third trimester of pregnancy (53%) compared with the first (47%) or second (37%) trimesters.
The efficacy of two doses against Omicron infection decreased over time, from 57% between birth and eight weeks to 40% after 16 weeks of age.
In addition to the 8,809 babies in the main analysis, 421 babies were born to mothers who received only their first dose of vaccine during pregnancy, which offered less protection against infection in babies than two or three doses (81% against Delta and 30% v. Omicron). ).
This is an observational study, so it cannot establish cause and the researchers cannot rule out the possibility that unmeasured factors, such as breastfeeding, may have been different between babies of vaccinated and unvaccinated mothers, which could affect Your results.
However, they used detailed information on hospital births, mother’s vaccination status and PCR test results, and the findings were similar after additional analyses, suggesting they are likely to be robust.
They note that mRNA vaccines are highly effective in preventing serious infections in pregnant women, who are at elevated risk of complications from Covid-19 compared to their non-pregnant counterparts.
“In this study, we show that maternal vaccination against Covid-19 during pregnancy could have dual benefits by also providing protection to their babies,” they conclude.
These results are consistent with previous studies from four different countries and are therefore reassuring, the researchers say in a linked editorial.
However, they point out that in the rapidly changing SARS-CoV-2 landscape, even solid conclusions cannot provide definitive answers to many practical questions.
As such, they say that while this study reinforces the value of maternal vaccination against Covid-19 during pregnancy, "further studies are needed to better inform vaccination recommendations in an evolving landscape of new SARS-CoV-2 strains." and new vaccines.
Conclusions Maternal vaccination against Covid-19 with a second dose during pregnancy was highly effective against Delta and moderately effective against Omicron infection and hospital admission in infants during the first six months of life. A third dose of vaccine reinforced protection against Omicron. The efficacy of two doses was greatest with maternal vaccination in the third trimester, and efficacy decreased in infants over eight weeks of age. |
