WASHINGTON, Nov 22: Two major studies have drawn attention to possible health risks associated with COVID-19 vaccination, including kidney injury and certain respiratory infections, though experts stress that the findings should be interpreted with caution.

A Korean study published in the International Journal of Infectious Diseases examined how infectious disease patterns changed during and after the COVID-19 pandemic and evaluated the effects of vaccination.

"While influenza-like illness dropped sharply during the early pandemic, upper respiratory infections and the common cold surged in 2023 and 2024, far above expected levels," said lead author Jihun Song, Ph.D., from the Department of Biomedical Informatics at Korea University College of Medicine. He added that pertussis cases increased more than 40-fold compared to historical trends.

The study found that individuals who received four or more COVID vaccine doses were less likely to contract flu-like illnesses and whooping cough, but were more susceptible to common colds and other mild respiratory infections.

"These mixed associations likely reflect complex changes in immunity, behavior, and healthcare use in the post-pandemic era," Song said. He emphasized that the study is observational and does not prove that the vaccine caused the rise in mild infections.

Experts noted that older adults and people with chronic conditions are more likely to receive multiple booster doses, which could influence results. Dr. Jacob Glanville, CEO of Centivax in San Francisco, pointed out that the group receiving more vaccines averaged 67 years old, while those with fewer doses averaged 37 to 47. "Older people go to the hospital more for colds and upper respiratory infections," he said.

Song also highlighted limitations, including changes in care-seeking behavior and healthcare utilization, as well as the absence of immunological data such as antibody levels or immune cell activity. "Our findings should not be interpreted as evidence that the vaccine increases or decreases specific infections, but rather as indicators of population-level trends that require further investigation," he said.

In a separate study published in the International Journal of Medical Sciences, COVID-19 vaccination was associated with a higher risk of acute kidney injury and dialysis within one year, though vaccinated individuals had lower overall mortality. Within 12 months, 15,809 vaccinated people developed acute kidney injury, compared with 11,081 unvaccinated. Dialysis was required in 1,513 vaccinated individuals versus 697 unvaccinated.

"Both risks were low in absolute terms, but the study is statistically well-controlled and there might be a real signal here," Glanville said. He added that the risk of kidney disease from COVID infection is higher than from vaccination, highlighting the need for further research.

The study acknowledged limitations, including gaps in electronic health records, missing data on vaccine doses, antibody levels, pre-existing kidney conditions, other health issues, and over-the-counter medications. Its retrospective design also means differences between groups may have affected outcomes.

Hua Wang, associate professor of materials science and engineering at the University of Illinois’ Grainger College of Engineering, urged caution in interpreting the results. "Both benefits and risks are reported in both studies, so we should not simply highlight potential negative effects," Wang said. She also noted the studies lacked information on SARS-CoV-2 infection rates among participants, which could have influenced results.

Dr. Marc Siegel, Fox News senior medical analyst, said, "These are massive studies that by no means prove that COVID vaccines cause kidney problems or increase susceptibility to respiratory infections, including flu. However, the associations found are worth investigating further." Siegel added that the studies may be biased if individuals receiving vaccines were already more prone to infections or kidney issues.