British Study Finds That Mild COVID-19 Causes Hidden Blood Cell Changes for Weeks
Nikhil Prasad Fact checked by:Thailand Medical News Team Jul 13, 2026 1 hour, 3 minutes ago
Medical News: Many people assume that mild COVID-19 leaves little lasting impact beyond a few days of cold-like symptoms. However, a new study has revealed that even mild infections can temporarily trigger significant changes in blood cells that continue for weeks after the virus is first detected.
New research shows that even mild COVID-19 can temporarily alter immune cells and platelet levels for weeks after infection
Researchers Track Blood Changes from the Earliest Stage of Infection
The study was conducted by researchers from the NIHR Health Protection Research Unit in Respiratory Infections, National Heart and Lung Institute, Imperial College London, the Department of Infectious Diseases, Imperial College London, the National Heart and Lung Institute, Imperial College London, and the Section of Virology, Department of Infectious Disease, Imperial College London, all in the United Kingdom.
The research followed 93 healthy adults with mild COVID-19 who had never been vaccinated or previously infected with SARS-CoV-2. Participants had no underlying medical conditions that could affect blood test results. Blood samples were collected at multiple time points over four weeks, allowing scientists to observe how routine blood counts changed from the beginning of infection through recovery.
Temporary Drop in Key Immune Cells
One of the most striking discoveries was a temporary reduction in two important types of white blood cells that help defend the body against infection.
About one-third of participants developed neutropenia, a condition in which neutrophil levels fall below the normal range. These cells are the body's first responders against invading microbes. More than one in five participants also experienced lymphopenia, meaning lower-than-normal lymphocyte counts. Lymphocytes play a central role in coordinating immune responses and producing antibodies.
Researchers believe these declines did not necessarily mean the immune system was failing. Instead, the immune cells were likely leaving the bloodstream and moving into infected tissues where they were needed most to fight the virus.
Platelets Show a Delayed Surge
Another unexpected finding involved platelets; the tiny blood components responsible for clotting.
Platelet counts dropped slightly during the earliest stage of infection before climbing significantly about two weeks later. In a small number of participants, platelet levels temporarily rose above the normal range.
Scientists also found that platelet size decreased before the increase in platelet numbers, suggesting that activated platelets were releasing their contents while participating in the body's response to infection. This
Medical News report highlights that these delayed platelet changes could help explain why blood clotting complications have occasionally been reported even after mild COVID-19.
Although most platelet
values remained within normal clinical limits, the researchers say these findings provide important insight into how the body continues responding long after symptoms begin improving.
Why These Findings Matter
Routine full blood count tests are inexpensive and widely available in hospitals and clinics worldwide. Until now, most previous studies focused on patients hospitalized with severe COVID-19, leaving scientists with limited information about what happens during mild infections, which account for the vast majority of COVID-19 cases.
The researchers found that neutrophil counts recovered quickly as participants improved, while platelet levels peaked later during recovery. These predictable patterns could help doctors better distinguish normal recovery from unexpected complications and provide valuable data for future mathematical models of immune responses to viral infections.
The study also offers a rare snapshot of how the human immune system reacted when SARS-CoV-2 first entered a population that had no previous immunity.
Conclusion
The findings demonstrate that even mild COVID-19 is far from biologically insignificant. Temporary reductions in important immune cells, followed by delayed platelet increases, reveal that the body continues mounting a carefully coordinated response well beyond the earliest phase of infection. These observations improve understanding of normal recovery, provide valuable reference data for future infectious disease research, and may eventually help clinicians better interpret routine blood tests during mild viral illnesses.
The study findings were published in the peer reviewed journal: PLOS One.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0353142
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Read Also:
https://www.thailandmedical.news/articles/coronavirus
https://www.thailandmedical.news/articles/long-covid
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