A new study has shown that the COVID-19 pandemic has had a long-term impact on the diagnosis rates of a number of serious conditions, including depression and asthma.

Researchers found that the number of diagnosed cases of these conditions has remained below expected levels after the pandemic, compared with pre-pandemic trends. This does not mean that these diseases have become less common, but rather that they are being diagnosed less frequently in medical practice.

The study was based on anonymized data from more than 29 million people in England, and its findings were published in The BMJ. It represents the first large-scale analysis to examine whether diagnostic rates recovered after the initial surge of COVID-19 began to subside.

The pandemic placed unprecedented strain on healthcare systems worldwide, sharply reducing the number of diagnoses across a wide range of conditions as resources were redirected toward fighting the virus and patients were less likely to seek medical care.

Among the 19 major conditions included in the analysis, depression was the most affected: diagnoses were approximately 27.7% lower than expected based on pre-COVID trends.

This means that nearly one-third of depression cases went undetected compared with what would have been anticipated. Asthma diagnoses also remained below normal levels, with about 16.4% fewer cases than projected.

Similar patterns were observed for other conditions, such as chronic obstructive pulmonary disease and osteoporosis.

This decline does not necessarily reflect a true reduction in disease prevalence; rather, it suggests that many people with these conditions may not have received timely medical evaluation or care during and after the pandemic.

The study also found that recovery in diagnostic rates was uneven across different social groups: in some ethnic and socioeconomically disadvantaged communities, diagnosis levels remain particularly low compared with pre-pandemic figures.