In the Journals

Maternal influenza vaccination does not increase risk for childhood morbidity

Data published in JAMA Pediatrics suggested maternal influenza A(H1N1) vaccination is not associated with an increased risk for early childhood morbidity among Danish children.

“Several studies investigating potential adverse effects of the pandemic A(H1N1) vaccine have supported that influenza A(H1N1) vaccination does not increase the risk for major pregnancy and birth adverse outcomes, such as birth defects, fetal death, intrauterine growth restriction and preterm delivery,” Anders Hviid, DrMedSci, of the department of epidemiology research at Statens Serum Institut, Copenhagen, Denmark, and colleagues wrote. “However, there is a dearth of studies looking at adverse effects in the offspring of A(H1N1)-vaccinated mothers beyond the perinatal period and into early childhood.”

Hviid and colleagues conducted a register-based cohort study to assess whether the pandemic influenza vaccine administered during pregnancy (inactivated AS03-adjuvanated split virion influenza A(H1N1) pdm09, Pandemrix; GlaxoSmithKline) increases the risk for early childhood morbidities.

The researchers examined outcomes for all singleton children (n=61,359) from pregnancies bordering the A(H1N1) vaccination campaign in Denmark from November 2009 to March 2010. According to study findings, the mothers of 55,048 children were unvaccinated, mothers of 349 were vaccinated in the first trimester and the mothers of 5,962 were vaccinated in the second and third trimesters. Hviid and colleagues matched exposed and unexposed offspring at a 1:4 ratio based on propensity scores. Mean age of the children at follow-up was 4.6 years.

Results from first hospitalization analysis showed that children exposed to maternal vaccination in the first trimester did not have an increased risk for child morbidity (RR = 1.17; 95% CI, 0.94-1.45). Further, children exposed in the second and third trimesters were not more likely to be hospitalized compared with unexposed children (RR = 0.93; 95% CI, 0.87-0.99).

Additionally, the researchers observed a 7% reduction in hospitalization risks for all hospitalizations until 5 years of age as 5% reduced risk for the first hospitalization.

“Although a reduced risk for both laboratory-confirmed influenza and influenza-like illness have been observed among infants of vaccinated mothers, this effect is attributable to maternally transferred antibodies and is restricted to early infancy in contrast to the effects observed in our study, which persisted throughout early childhood and comprised infectious diseases other than influenza-like illness,” Hviid and colleagues wrote. “Further studies looking at individual infectious diseases in greater detail would be necessary to confirm and elucidate the reduced risks observed in our cohort.” – by Kate Sherrer

Disclosure: Hviid reports receiving a Hallas-Møller stipend from the Novo Nordisk Foundation. Please see the full study for a list of all other authors’ financial disclosures.

Data published in JAMA Pediatrics suggested maternal influenza A(H1N1) vaccination is not associated with an increased risk for early childhood morbidity among Danish children.

“Several studies investigating potential adverse effects of the pandemic A(H1N1) vaccine have supported that influenza A(H1N1) vaccination does not increase the risk for major pregnancy and birth adverse outcomes, such as birth defects, fetal death, intrauterine growth restriction and preterm delivery,” Anders Hviid, DrMedSci, of the department of epidemiology research at Statens Serum Institut, Copenhagen, Denmark, and colleagues wrote. “However, there is a dearth of studies looking at adverse effects in the offspring of A(H1N1)-vaccinated mothers beyond the perinatal period and into early childhood.”

Hviid and colleagues conducted a register-based cohort study to assess whether the pandemic influenza vaccine administered during pregnancy (inactivated AS03-adjuvanated split virion influenza A(H1N1) pdm09, Pandemrix; GlaxoSmithKline) increases the risk for early childhood morbidities.

The researchers examined outcomes for all singleton children (n=61,359) from pregnancies bordering the A(H1N1) vaccination campaign in Denmark from November 2009 to March 2010. According to study findings, the mothers of 55,048 children were unvaccinated, mothers of 349 were vaccinated in the first trimester and the mothers of 5,962 were vaccinated in the second and third trimesters. Hviid and colleagues matched exposed and unexposed offspring at a 1:4 ratio based on propensity scores. Mean age of the children at follow-up was 4.6 years.

Results from first hospitalization analysis showed that children exposed to maternal vaccination in the first trimester did not have an increased risk for child morbidity (RR = 1.17; 95% CI, 0.94-1.45). Further, children exposed in the second and third trimesters were not more likely to be hospitalized compared with unexposed children (RR = 0.93; 95% CI, 0.87-0.99).

Additionally, the researchers observed a 7% reduction in hospitalization risks for all hospitalizations until 5 years of age as 5% reduced risk for the first hospitalization.

“Although a reduced risk for both laboratory-confirmed influenza and influenza-like illness have been observed among infants of vaccinated mothers, this effect is attributable to maternally transferred antibodies and is restricted to early infancy in contrast to the effects observed in our study, which persisted throughout early childhood and comprised infectious diseases other than influenza-like illness,” Hviid and colleagues wrote. “Further studies looking at individual infectious diseases in greater detail would be necessary to confirm and elucidate the reduced risks observed in our cohort.” – by Kate Sherrer

Disclosure: Hviid reports receiving a Hallas-Møller stipend from the Novo Nordisk Foundation. Please see the full study for a list of all other authors’ financial disclosures.