Breastfeeding May Confer Long-Term Immunity Against Emerging Infectious Pathogens—Ecological Evidence over 2 Full Years of the COVID-19 Epidemic in Georgia, United States

Objective: Long-term immunity acquired maternally against infectious pathogens has been reported in animal studies, but epidemiological evidence remains lacking. To assess long-term maternal immunity in humans against infectious pathogens, we examined COVID-19 disease burden in communities with varying breastfeeding practices. Methods: Using data from 159 counties in Georgia, the United States, from March 1, 2020, through February 28, 2022, we calculated the daily incidence, mortality, and fatality rates of COVID-19 and estimated rate ratios (RRs) in counties with low (<62%, n = 36) and moderate breastfeeding initiation rates (BFIRs) (62–79%, n = 81) compared to counties with high BFIRs (≥79%, n = 42) adjusted for counties’ sociodemographic and quantified indicators of public health interventions. Results: More than 80% of 2 million cases involved individuals aged 18 or older. The daily incidence and mortality curves in the counties with high BFIRs lagged 2 weeks behind those in the counties with low BFIRs. Daily mortality reached 10 deaths per million during every major surge in low BFIR counties, but in high BFIR counties, this occurred only during the 2020–2021 winter spike. Compared to high BFIR counties, counties with low BFIRs had a daily incident RR of 2.95 (95% CI = 1.11, 6.00) in rural counties and 1.45 (1.03, 2.04) in urban counties on February 28, 2022, the cutoff date. Conclusions: A significantly higher COVID-19 incidence occurred in low BFIR counties compared to that in high BFIR counties. Breastfeeding may confer long-term immunity against emerging infectious pathogens by enhancing an individual’s biological immunity or strengthening the community’s social defense.