Fewer Boys Were Born After Brazil's Gamma COVID-19 Wave and Pele's Death: A National Time-Series Analysis
This national time-series analysis of over 81 million Brazilian births reveals a statistically significant decline in the sex ratio at birth following the April 2021 Gamma COVID-19 wave and the April 2023 death of Pelé, suggesting that major societal stressors and behavioral changes can temporarily alter the proportion of male births.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Every year, slightly more boys are born than girls. This ratio is one of the most stable numbers in human biology, holding steady across centuries and cultures. Yet, history shows that this balance can tip temporarily when a population faces a sudden, severe shock. When a society endures a war, a natural disaster, or a devastating epidemic, the number of male births often drops a few months later. Scientists believe this happens because male fetuses are slightly more fragile than female ones; when a mother is under extreme stress, her body may be more likely to lose a male pregnancy before birth. This biological sensitivity turns the birth ratio into a kind of silent barometer, measuring the invisible weight of collective trauma on a nation's families.
A team of researchers decided to test whether this pattern held true during the COVID-19 pandemic in Brazil. They focused on a specific moment of intense crisis: the "Gamma" wave of the virus in early 2021. This was a particularly deadly period for Brazil, with the highest number of deaths occurring in April 2021. The scientists asked a straightforward question: did the birth ratio change in the months following this peak of suffering? To find out, they looked at a massive dataset containing more than 81 million births recorded over nearly three decades. By comparing the actual number of boys born in 2021 against what statistical models predicted based on previous years, they could see if the pandemic had left a mark on the sex of newborns.
The results showed a clear, temporary shift. In July 2021, exactly three months after the April peak in deaths, the number of boys born in Brazil dropped below the expected level. Instead of the usual proportion of about 51.2 percent male births, the figure fell to just under 51 percent. This dip was not a random fluctuation; it was low enough to fall outside the range of normal variation the researchers had calculated. The effect was seen across the entire country, from the south to the north, but it was most pronounced in the northern region, where the deadly Gamma variant was first identified. The researchers used computer simulations to check how rare this event was, finding that a drop of this size and consistency across the whole country would happen by pure chance only about once in every 200 times.
The study also looked at the years that followed to see if other major events left similar marks. In early 2023, nine months after Brazil officially ended its public health emergency, the birth ratio actually rose, with more boys being born than expected. The authors suggest this might reflect a change in behavior, as couples who had been separated or restricted during lockdowns may have conceived more children once restrictions were lifted. Later that same year, in April 2023, the ratio dropped again. This decline occurred roughly four months after the death of Pelé, the legendary Brazilian football player. The timing mirrors a similar drop in male births in the United Kingdom that happened after the death of Princess Diana, suggesting that the grief of a nation can sometimes ripple through its biology. However, the researchers are careful to note that these later observations are merely suggestions for future study, not proven facts.
The paper does not claim to know exactly why these changes happened. It cannot say whether the stress of the pandemic caused mothers to lose male fetuses, or if it changed the timing of when couples tried to have children. The data comes from national records, not from individual families, so the specific reasons remain hidden. What the study does confirm is that Brazil's birth numbers are sensitive enough to record the impact of a major national crisis. The drop in boys born in July 2021 stands as a statistical echo of the suffering that occurred three months prior, a quiet signal in the data that a population had been deeply shaken. While the long-term trend of fewer babies being born in Brazil continues due to broader social changes, this specific, short-lived dip in the sex ratio offers a glimpse into how human biology responds to the weight of history.
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