BACKGROUND AND PURPOSE:

• Hayek et al. (Science, 2022) estimated the protection provided to children through parental vaccination with the Pfizer vaccine

METHODS:

• Retrospective cohort study
• Population
  • Households composed of two spouses
  • Both spouses within the 25 to 80 year range
  • Children under the minimal age of vaccine eligibility
• Exposures
  • 0, 1 or 2 fully vaccinated parents
    • In the later period of this study, full vaccination included a booster
• Study design
  • There were two study periods
    • Early: January 2021 through March 2021 (dominant strain Alpha, vaccination available to those 16 and older)
    • Late: July 2021 through September 2021 (dominant strain Delta, vaccination available to those 12 and older)
  • Vaccine effectiveness was defined as one minus the incidence rate ratio (VE=1-IRR) of one or two fully vaccinated parents vs no fully vaccinated parents
• Primary outcomes
  • SARS-CoV-2 infection
  • Indirect vaccine effectiveness (VE)

RESULTS:

• Population demographics
  • Early period
    • 400,733 unvaccinated children from 155,305 households who contributed 2,116,306 person-weeks of follow-up
  • Late period
    • 181,307 unvaccinated children from 76,621 households who contributed 1,089,191 person-weeks of follow-up
• In the early period (Alpha dominant strain) vaccinated parents reduced the risk of infection in unvaccinated children
  • Single vaccinated parent: 26.0% reduced risk of infection
  • Two vaccinated parents: 71.7% reduced risk of infection
• In the late period (Delta dominant strain), vaccinated parents still reduced the risk of infection for unvaccinated children
  • Single vaccinated parent:  20.8% reduced risk of infection
  • Two vaccinated parents: 58.1% reduced risk of infection

CONCLUSION:

• Parental vaccination was shown to confer an indirect protection for unvaccinated children
• The authors state

Indirect vaccine effects are mediated by two main mechanisms: First, by protecting potential contacts, vaccination reduces the likelihood that subjects will encounter an infectious individual

Second, vaccination may reduce the infectiousness of vaccinated individuals who do acquire the infection

Learn More – Primary Sources:

Indirect protection of children from SARS-CoV-2 infection through parental vaccination

Related ObG Topics: