Internet searches related to vitamin A and cod liver oil increased during the 2025 US measles outbreak in temporal association with media statements promoting vitamin A as a measles treatment, according to a Research Letter published in JAMA Network Open.
Vaccination remains the only proven prophylactic against measles. Vitamin A may be administered under medical supervision to support recovery from measles, but it does not prevent measles and can be toxic if dosed incorrectly. Cod liver oil also contains high levels of vitamin A.
Researchers conducted a cross-sectional study using Google Search Trends as proxy indicators of public interest. They examined daily US search activity from January 1 to June 1, 2025, for the search terms “vitamin A” measles and “cod liver” measles.
The study used relative search fraction, a normalized Google Trends measure of search interest relative to all queries within a specified period and location. Because Google Trends values are normalized rather than absolute search counts, they do not show the number of searches or the size of the interested population.
To improve robustness, the researchers calculated mean relative search fraction estimates and 95% CIs from twice-daily Google Search Trends searches conducted over 12 days. Because the study derived relative search fraction estimates from repeated Google Search Trends pulls, the reported 95% CIs should be interpreted in the context of that search-data method rather than as clinical outcome uncertainty.
The researchers identified peaks in search activity using anomaly detection and compared search interest with governmental media statements. They then used interrupted time-series analysis with Bayesian segmented regression to assess whether media coverage was associated with changes in Google Search Trends. The analysis adjusted for potential media exposure bias, and observed search activity was compared with counterfactual estimates adjusted for daily measles case counts.
Search interest for both terms was minimal until February 25, 2025. Relative search fraction for “vitamin A” measles rose to 44% on February 26 and was highest on March 22. Because relative search fraction is normalized to the peak within the analyzed period, the peak value reflects the top point in the Google Trends series rather than an absolute measure of search volume. Searches for “cod liver” measles peaked on March 5.
Multiple governmental media statements promoting vitamin A as a measles treatment began on February 19. The researchers noted that although their formal analysis focused on government statements, several nongovernmental figures, including Joe Rogan and Suzanne Humphries, also issued statements. These nongovernmental statements were not separately modeled as exposures in the interrupted time-series analysis.
In interrupted time-series analyses, vitamin A search interest was a mean 7.5 percentage points higher than the counterfactual estimate after the onset of media coverage. Search interest in cod liver oil was 1.3 percentage points higher than expected.
The findings should be interpreted as an association, not evidence that media statements caused the search increase. The model compared observed search activity with counterfactual estimates adjusted for daily measles case counts. The published Research Letter did not report analyses using control search terms.
The study could not determine whether increased search activity translated into vitamin A use, cod liver oil use, dosing behavior, poison exposures, or other clinical outcomes. The researchers cited a separate report from America’s Poison Centers describing a 38.7% increase in vitamin A exposures between January and March 2025, but those poison center data were not linked at the individual level to Google searches.
The analysis was limited to Google Search Trends data and therefore reflects search interest rather than broader public behavior or clinical outcomes. Additional sensitivity analyses were made available through the researchers’ GitHub repository.
The study followed the Strengthening the Reporting of Observational Studies in Epidemiology reporting guideline for cross-sectional studies. Ethical approval and informed consent were not required because the analysis used publicly available, anonymous data.
Maimuna Shahnaz Majumder, PhD, reported receiving research funding from Moderna unrelated to the current study. No other conflicts of interest were disclosed. The study was supported by the National Science Foundation, the National Institutes of Health, and a postdoctoral fellowship from the German National Academy of Sciences Leopoldina awarded to Anne Christine Bischops, MD.
Source: JAMA Network Open
