BCG Vaccine Study Reveals Wide Differences in Children’s Immune Responses After Vaccination

2026-07-13 04:15:56 Health and Fitness

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A new study from researchers in Iraq has found that children vaccinated with the Bacille Calmette-Guérin (BCG) vaccine show highly varied immune responses, highlighting why some children may develop stronger protection than others after vaccination. The findings also suggest that the presence or absence of a visible BCG scar does not always reflect the strength of immune protection.

The research, published in the Asian Journal of Immunology, investigated immune signaling molecules known as Interleukin-2 (IL-2) and Interleukin-4 (IL-4) in vaccinated and unvaccinated children. These cytokines play an important role in regulating immune defense against infections, including tuberculosis.

Researchers studied 90 healthy children between six months and 10 years of age at Diwanyah Child and Maternity Hospital in Iraq. Among them, 60 children had received the BCG vaccine, while 30 unvaccinated children served as controls. Half of the vaccinated children had visible BCG scars, while the other half did not.

The team measured IL-2 and IL-4 levels in blood samples using ELISA laboratory testing methods. Results showed that vaccinated children generally had higher immune-response cytokine levels than unvaccinated children. However, responses varied significantly between individuals. Some vaccinated children showed very strong immune activity, while others had levels similar to or even lower than unvaccinated controls.

The study found average IL-2 levels of 887.2 pg/ml in scar-bearing vaccinated children and 988.4 pg/ml in non-scar-bearing vaccinated children, compared with 548.8 pg/ml in unvaccinated controls. IL-4 levels were also substantially higher among vaccinated groups than controls.

According to the researchers, these findings demonstrate that immune responses after BCG vaccination are “heterogenic and divergent,” meaning children do not respond to the vaccine in exactly the same way.

Lead authors Ibrahim M. S. Shnawa and Tiba A. Karim explained that several factors could contribute to these differences, including age-related immune decline, immune-suppressive tissue environments, and differences in how children’s immune systems recognize vaccine components.

“Not all the BCG scar bearing child have good reactive immunity and not all non-BCG scar bearing child have poor immune reactivity,” the researchers wrote.

The study also identified three major immune-response groups among vaccinated children: low responders, moderate responders, and high responders. Researchers described these response patterns as following a “Gaussian distribution,” meaning immune responses spread across a broad natural range within the population.

BCG remains one of the world’s most widely used vaccines for tuberculosis prevention and is also known for broader immune effects beyond TB protection. Researchers say understanding how children respond differently to the vaccine may help improve vaccination strategies and future immune-based therapies.

The authors noted that some children with lower cytokine responses may experience “immune waning” as they age, while others may react differently because of specific vaccine epitopes that can suppress or regulate immune activity.

Conclusion

The study concludes that BCG vaccination triggers both IL-2 and IL-4 immune responses in children, but these responses vary widely from one child to another. Researchers emphasize that visible vaccine scars alone should not be considered a reliable indicator of immune strength. The findings may help scientists better understand childhood vaccine immunity and guide future research into improving vaccine effectiveness and personalized immune monitoring.

References

Shnawa, I. M. S., & Karim, T. A. (2024). The Interleukin -2 and Interleukin -4 Response Profiles in Pediatric BCG Vaccinee. Asian Journal of Immunology, 7(1), 31–38. https://doi.org/10.9734/aji/2024/v7i1127

Dash, N., Verghese, V. P., Rose, W., Michael, J. S., Rebekah, G., Venkatesan, M., & Chacko, A. (2022). Clinical, Microbiological Profile and Treatment Outcomes of Infants with BCG Adenitis: A Retrospective Study. Journal of tropical pediatrics, 68(6), fmac094. https://doi.org/10.1093/tropej/fmac094