The gut microbiome plays a crucial role in the development of the immune system, especially in infants who are exposed to microorganisms during and immediately after birth. This exposure continues from their environment over the next six months, influenced by feeding practices and interaction with other humans. However, during the COVID-19 pandemic, mass lockdowns significantly reduced these opportunities for infants.
The CORAL (Impact of Corona Virus Pandemic on Allergic and Autoimmune Dysregulation in Infants Born During Lockdown) study was initiated to examine the impact of social distancing measures on the gut microbiome of infants who spent most of their early life with limited social contact.
Study Design and Methodology
The CORAL study included 360 infants in Ireland born during the first three months of the COVID-19 pandemic (March-May 2020). The demographics of these infants reflected the general population, with the exception of higher maternal education levels. Social distancing measures were found to be effective, as only 4.7% of the infants had an antibody response to COVID-19 at 12 months. Families in the CORAL cohort had an average of four social contacts outside the home when the infants were six months old, and 25% of the infants had not met a child their own age by 12 months.
Gut Microbiome Analysis
Faecal samples were used to investigate the gut microbiome of the infants. The mode of delivery influenced the gut microbiome composition, with differences noted between infants delivered via caesarean-section and vaginal birth at 6 and 12 months of age. Post-natal antibiotic use also showed some influence, but the low percentage of antibiotic use limited the analysis. The presence of siblings and pets was also seen to have an impact on the gut microbiome.
Diet, particularly breastfeeding, was found to be the main determinant of microbiome composition, surpassing the mode of birth. The consumption of beans, nuts, seeds, oils, and cow’s milk significantly contributed to the microbiome composition at 12 months. Interestingly, oil, beans, and nuts were associated with a microbiome composition similar to that of breastfeeding, whereas animal-derived products like cow’s milk had the opposite effect.
Comparing Pre-Pandemic and Pandemic-Era Infants
The microbiome composition of the CORAL cohort was compared to that of infants from pre-pandemic studies. The CORAL cohort had significantly lower levels of bacteria types typically transmitted from person to person. However, the overall composition and development of the microbiome followed the expected pre-pandemic pattern and even showed an increased abundance of beneficial bacteria. This suggests that the mother and close family members are the most crucial sources of microorganisms for infants.
Allergy Development
The study also investigated the association between social distancing, microbiome composition, and allergic disease. Levels of allergic disease in the CORAL cohort were not higher than expected. However, the presence of one type of bacteria (Bifidobacterium) was associated with allergic disease, and some subtypes were linked to specific disease presentations.
Conclusion
In summary, the CORAL study reveals that the gut microbiome of infants born during COVID-19 pandemic social distancing periods differs from that of pre-pandemic infants. However, there was no evidence that these differences affected the development of allergic diseases. This study provides valuable insights into the gut microbiome of a large group of infants during a unique time period. Further research may explore the effects of antibiotic use, infection avoidance, and increases in breastfeeding.
References
- Olin A, Acevedo N, Lakshmikanth T, Chen Y, Johansson C, Alm J, Scheynius A, Brodin P. Longitudinal analyses of development of the immune system during the first five years of life in relation to lifestyle. Allergy. 2022 May;77(5):1583-1595. doi: 10.1111/all.15232. Epub 2022 Feb 16. PMID: 35094423.
- Hurley S, Franklin R, McCallion N, Fitzsimons J, Byrne A, White M, O'Mahony L, Hourihane J. Allergic Outcomes at 2 years in children born during COVID-19 lockdown: the CORAL study. J Allergy Clin Immunol. 2023 Feb;151(2):AB167. doi: 10.1016/j.jaci.2022.12.522. Epub 2023 Feb 3. PMCID: PMC9895816.
