Fewer Boys Were Born After Brazil's Gamma COVID-19 Wave and Pele's Death: A National Time-Series Analysis

Abstract

The sex ratio at birth (SRB), or secondary sex ratio, is stable, with more boys born alive, but shifts after major events. Acute stress may reduce SRB through disproportionate male fetal loss, while sexual intercourse patterns around conception are associated with offspring sex. We examined whether Brazils April 2021 Gamma-wave mortality peak was followed by an SRB decline within the previously reported stress-sensitive 3-5-month window. We analysed >81 million live births (1997-2024) from Brazils Live Birth Information System (SINASC) using pre-pandemic autoregressive forecasts with 95% prediction intervals (PIs). In July 2021, SRB was 50.951% versus 51.185% expected, below the 95% PI (50.968-51.402%), indicating fewer boys. All five macroregions were below expectation, largest in the North, including Amazonas, where Gamma was first identified. Monte Carlo simulation showed that, under usual SRB patterns, a decline with this timing and consistency across Brazil would occur about once in 200 simulations (probability 0.00467), making July 2021 unusual. In February 2023, SRB was 51.441% versus 51.220% expected, above the 95% PI (51.003-51.438%), indicating more boys, nine months after Brazil ended its COVID-19 emergency, suggesting increased sexual intercourse after pandemic relaxation. In April 2023, SRB was 50.956% versus 51.221% expected, below the 95% PI (51.004-51.439%), indicating fewer boys, four months after Peles death. A comparable UK decline followed Princess Dianas death 4-5 months later. Gamma was prespecified; later observations are hypothesis-generating. These findings highlight SRBs population-level utility and warrant investigation of stress-related and behavioural pathways; ecological design precludes causality.

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BibTeX RIS

BibTeX

@misc{leite2026fewer,
  title = {{Fewer Boys Were Born After Brazil's Gamma COVID-19 Wave and Pele's Death: A National Time-Series Analysis}},
  author = {D. F. Leite and R. Masukume and P. T. Chimberengwa and V. Grech and W. Mapanga and G. Masukume and G. Liczbinska},
  howpublished = {medRxiv},
  year = {2026},
  month = sep,
  doi = {10.64898/2026.09.28.26364140},
  url = {https://www.medrxiv.org/content/10.64898/2026.09.28.26364140v1},
  note = {CC BY},
}

RIS

TY  - UNPB
TI  - Fewer Boys Were Born After Brazil's Gamma COVID-19 Wave and Pele's Death: A National Time-Series Analysis
AU  - D. F. Leite
AU  - R. Masukume
AU  - P. T. Chimberengwa
AU  - V. Grech
AU  - W. Mapanga
AU  - G. Masukume
AU  - G. Liczbinska
PY  - 2026
DA  - 2026/09/28
PB  - medRxiv
DO  - 10.64898/2026.09.28.26364140
UR  - https://www.medrxiv.org/content/10.64898/2026.09.28.26364140v1
AB  - The sex ratio at birth (SRB), or secondary sex ratio, is stable, with more boys born alive, but shifts after major events. Acute stress may reduce SRB through disproportionate male fetal loss, while sexual intercourse patterns around conception are associated with offspring sex. We examined whether Brazils April 2021 Gamma-wave mortality peak was followed by an SRB decline within the previously reported stress-sensitive 3-5-month window. We analysed >81 million live births (1997-2024) from Brazils Live Birth Information System (SINASC) using pre-pandemic autoregressive forecasts with 95% prediction intervals (PIs). In July 2021, SRB was 50.951% versus 51.185% expected, below the 95% PI (50.968-51.402%), indicating fewer boys. All five macroregions were below expectation, largest in the North, including Amazonas, where Gamma was first identified. Monte Carlo simulation showed that, under usual SRB patterns, a decline with this timing and consistency across Brazil would occur about once in 200 simulations (probability 0.00467), making July 2021 unusual. In February 2023, SRB was 51.441% versus 51.220% expected, above the 95% PI (51.003-51.438%), indicating more boys, nine months after Brazil ended its COVID-19 emergency, suggesting increased sexual intercourse after pandemic relaxation. In April 2023, SRB was 50.956% versus 51.221% expected, below the 95% PI (51.004-51.439%), indicating fewer boys, four months after Peles death. A comparable UK decline followed Princess Dianas death 4-5 months later. Gamma was prespecified; later observations are hypothesis-generating. These findings highlight SRBs population-level utility and warrant investigation of stress-related and behavioural pathways; ecological design precludes causality.
ER  -

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