Maternal immunization offers an opportunity to protect the mother and fetus, but also passes this protection on to the infant after birth.
Key Evidence: In Brazil, where pertussis cases have climbed, mainly in infants <4 months of age, vaccinating pregnant women with Tdap vaccine at the same coverage rate as influenza vaccination in pregnant women (57%) would reduce pertussis cases in children under 1 year of age by 41%, deaths by 43%, and would be cost-effective, according to the WHO thresholds.
Key Evidence: In Japan, which has experienced a re-emergence of pertussis among adolescents and adults, vaccinating pregnant women with the Tdap vaccine would be cost effective in preventing the illness in young infants (<3 months of age) and in mothers, according to the WHO definition of cost effectiveness. This is true even if only 50% of pregnant women receive the vaccine.
Key Evidence: Pertussis causes nearly 200,000 deaths in children worldwide, nearly all in infants too young to be vaccinated. Vaccinating pregnant women against pertussis with a single dose of Tdap vaccine would be 89% effective in protecting infants against the disease over their first 2 months of life and would reduce pertussis incidence in newborns in the U.S. by 68% (assuming 75% of mothers are vaccinated).
Key Evidence: A study in Australia estimated that adding dTpa vaccination for pregnant women to the current pertussis immunization program for children would prevent an additional 8,800 symptomatic pertussis cases (mostly unreported) and 146 hospitalizations each year in all ages, including infants and their mothers, as well as one death every 22 months. The study found maternal pertussis vaccination to be cost-effective.
From the VoICE Editors: Note: The formulation used in this study is abbreviated dTpa.
Key Evidence: A large study in California involving nearly 150,000 newborns found that vaccinating pregnant women with the Tdap vaccine provided 91% protection against pertussis infection among infants under 2 months of age and 88% protection before the infants had any vaccinations. The study also showed that vaccinating mothers during their pregnancy did not reduce the effectiveness of infant vaccination but that maternal Tdap vaccination provided additional protection to the infants through their first year of life.
A pooled analysis of three randomized controlled trials conducted in Nepal, Mali, and South Africa between 2011 and 2014 found that immunization during pregnancy provided protection against influenza to young infants from birth through 4 months of age. Protection against infant influenza was greatest in the first 2 months of life, with 56% efficacy, and the pooled efficacy of maternal vaccination to prevent infant laboratory-confirmed influenza up to 6 months of age was 35%.
Key Evidence: In Argentina, more than 50% of deaths due to pertussis occurred in infants younger than 2 months of age — too young to be vaccinated in the country. The impact of maternal pertussis vaccination in protecting their infants against the disease reduced the incidence of pertussis in infants less than 2 months old by half, when comparing states with high and low maternal vaccination rates.
Key Evidence: Infants born to mothers who reported receiving influenza vaccination during pregnancy had a 64% lower risk of getting influenza-like illness in their first 6 months of life, a 70% lower risk of laboratory-confirmed influenza, and an 81% lower chance of being hospitalized with influenza than infants whose mothers did not report getting the influenza vaccine during pregnancy. Since influenza vaccines are not effective in children less than 6 months old, immunizing pregnant women against influenza is a public health priority.
From the VoICE Editors: Data is from a study spanning more than 8 years at a large healthcare organization in the Western U.S.
Key Evidence: An analysis of data from three studies showed that the rates of severe pneumonia in infants in their first six months of life was 20% lower overall in infants whose mothers received the influenza vaccination during pregnancy than in infants whose mothers had not, and the rates of severe pneumonia was 56% lower during periods when influenza circulation was highest. These findings correspond with evidence that influenza infection predisposes individuals to pneumococcal infection.
From the VoICE Editors: The incidence rate of severe pneumonia in the vaccine group compared to the control group was 43% lower in South Africa, 31% lower in Nepal, but not significantly different in Mali.
Key Evidence: Vaccinating women during their second or third trimester of pregnancy with the Tdap vaccine was 81% effective in preventing pertussis in their infants in the first two months of life, according to a case-control study in Argentina.
From the VoICE Editors: This is one of the first studies to measure the effectiveness of maternal pertussis vaccination in a middle-income country and its findings support Argentina’s decision to introduce the vaccine.