Protection against respiratory infection shrank with every rerun
The same team pooled the trials three times. The odds reduction went from 12 percent in 2017 to 8 percent in 2021 to 6 percent in 2025, no longer statistically significant.
What the study found
Each rerun of the same analysis found less protection
The same team pooled the respiratory infection trials three times as more accumulated. The odds reduction went from 12 percent in 2017 to 8 percent in 2021 to 6 percent in 2025, where the confidence interval reached 1.00 and the result stopped being statistically significant.
The caveat · Small null trials may be unpublished
The 2025 funnel plot leans left, the pattern seen when small trials that found nothing were never published. All three versions pool trials running from infancy to age 95 across many countries, so the pooled group is not one population. The 2017 version worked from individual participant records and the later two from summary numbers, which is a weaker footing for any subgroup.
What we don't know
Protection against respiratory infection shrank each time the same analysis was rerun with more trials. Whether the effect was never there, or the newer trials enrolled people with less to gain, these analyses cannot separate.