All-cause mortality patterns according to vaccination timing and dose number among Japanese non-elderly adults: a proxy risk-group analysis
This study of non-elderly adults in Matsudo City, Japan, found that while confounding by indication influenced early mortality patterns, all-cause mortality rates generally increased with the number of COVID-19 vaccine doses, even among proxy high-risk groups, suggesting that the observed trends are not fully explained by bias alone.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine a massive public health experiment in a Japanese city called Matsudo, involving about 500,000 people who aren't yet elderly (ages 20 to 64). The researchers wanted to understand a confusing puzzle: Why did people who got the most COVID-19 vaccine shots seem to die more often than those who got fewer shots?
Usually, when we see this pattern, we think, "Ah, the sickest people are getting the most shots because they need them most." This is called "confounding by indication." It's like seeing a hospital full of people with broken legs and concluding that hospitals cause broken legs. The reality is that people with broken legs go to the hospital.
However, this study suggests the story is a bit more complicated than just "sick people get more shots." Here is how the researchers broke it down, using simple analogies:
The Setup: The "High-Risk" vs. "Low-Risk" Groups
The researchers didn't just count how many shots people got; they looked at when people got them.
- The "Voluntary" Group (Proxy High-Risk): These were people who jumped the gun. They got their 4th, 5th, 6th, or 7th dose early, before the government officially told everyone to get it. The researchers assume these people felt they were more vulnerable, so they rushed to get vaccinated. Think of them as the people who buy extra umbrellas the moment the sky turns a tiny bit gray.
- The "Wait-and-See" Group (Proxy Low-Risk): These people waited until the official government schedule told them to get their next shot. They are like the people who only buy an umbrella when it's already pouring rain.
The Findings: The Pattern That Didn't Fit
The researchers looked at death rates in two timeframes: the first 6 months after a shot, and the 6 months after that (but before the next shot).
1. The "Sicker People Get More Shots" Theory (Partially True)
As expected, the "Wait-and-See" groups (who got shots later) had lower death rates than the "Voluntary" groups. This supports the idea that the people who rushed to get early shots were indeed sicker or more worried about their health to begin with.
2. The Twist: The "Stopping" Pattern
Here is where the puzzle gets interesting. The researchers looked at people who stopped getting shots.
- If you are a very sick person, you would expect you to keep going to the doctor (or getting shots) as long as you can.
- But the data showed that people who stopped getting their next shot actually had higher death rates in the months after they stopped, compared to the people who kept going and got their next shot.
The Metaphor: Imagine a race where the runners who drop out of the race are dying more often than the runners who keep running. If the "sick" people were the ones getting extra shots, the "dropouts" should be the healthy ones. But the opposite happened. This suggests a "Healthy Vaccinee Bias": perhaps people who were feeling too sick to get another shot were the ones who ended up dying, while the people who felt well enough to line up for the next shot were healthier.
3. The Dose Count Problem
Even when the researchers looked only at the "Voluntary" (high-risk) groups, the death rate still went up as the number of shots increased.
- Getting a 6th or 7th shot was associated with higher death rates than getting a 4th or 5th shot, even among people who were already considered "high risk."
- It's as if, within the group of people who were already worried enough to get early shots, the ones who got the most shots were still the ones with the highest death rates.
The Conclusion: A Mystery Not Fully Solved
The authors conclude that while it is true that sicker people tend to get more shots (confounding by indication), that does not fully explain why the death rates keep climbing with every additional dose.
They are essentially saying: "We see a pattern where more shots = more deaths. We know some of this is because sicker people get more shots. But even when we try to account for that, the pattern remains. It's possible that the people who were too sick to get the next shot died, creating a misleading picture, or there are other factors we haven't measured yet."
What they did NOT say:
- They did not claim the vaccines caused the deaths.
- They did not say people should stop getting vaccinated.
- They did not provide a final answer on why this is happening.
Instead, they are holding up a mirror to the data and saying, "The numbers show a strange relationship between the number of shots and death rates that is too complex to be explained just by 'sick people getting more shots.' We need more research that looks at specific diseases, money, and social factors to understand the full picture."
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