Palatine tonsils are small clusters of lymphoid tissue located in the pharynx. As part of the immune system, they help protect the body from bacterial and viral infections of the upper respiratory tract. Tonsils are particularly active in childhood but atrophy with age. Some individuals undergo tonsillectomy to treat chronic tonsillitis or obstructive sleep apnea.
Although tonsil removal does not significantly affect immune functions, several studies have suggested tonsillectomy may be associated with an increased risk of certain diseases later in life, including acute myocardial infarction, periodontitis, and cancer.
Chinese and Swedish researchers examined how the absence of tonsils influences susceptibility to COVID-19 and its progression.
Previous Studies Have Indicated That:
- Individuals who had undergone tonsillectomy had a lower-than-expected frequency of positive SARS-CoV-2 tests. However, no association was found between tonsillectomy and COVID-19 severity.
- Among COVID-19 patients, those with a history of tonsillectomy had a higher likelihood of developing fever, temperatures above 39°C, chills, and malaise. Tonsillectomy did not affect hospitalization risk.
- Patients with chronic tonsillitis, chronic adenoiditis, or peritonsillar abscess who had undergone tonsillectomy had a lower risk of COVID-19 and mortality. However, the effect of tonsillectomy on SARS-CoV-2 infection susceptibility was not statistically significant.
- Tonsillectomy was associated with an increased long-term risk of respiratory and infectious diseases.
- Tonsillectomy had no impact or reduced the risk of hospitalization for acute respiratory infections.
Researchers analyzed large-scale population data from the UK Biobank and the Swedish Apolipoprotein Mortality Risk (AMORIS) cohort to explore this issue further. The study included data from approximately 511,000 individuals, making it the most extensive investigation into the association between tonsillectomy and COVID-19 severity.
Study Findings
People who had undergone tonsillectomy were less likely to develop mild and severe COVID-19 than those who still had their tonsils. This trend remained consistent regardless of sex, age, socioeconomic status, and genetic predisposition to severe COVID-19. The observed association was unlikely to be influenced by changes in the blood’s inflammatory, lipid, and metabolic biomarkers. A weak correlation was noted between tonsillectomy and lymphocytes, neutrophils, inflammation biomarkers (NLR, PLR, and SII), albumin, glucose, total cholesterol, low-density lipoprotein cholesterol, and apolipoprotein B.
Possible Reasons for Reduced COVID-19 Risk
- Tonsils may serve as a reservoir for SARS-CoV-2, facilitating viral spread.
Korean scientists have demonstrated that tonsils can be a potential target for the SARS-CoV-2 coronavirus. To investigate this, they created tonsil organoids—three-dimensional cell structures derived from human tonsil epithelial cells that mimic the structure and function of real tonsils. These organoids responded to pathogens similarly to tonsil tissues in the body, producing pro-inflammatory signaling molecules (IL-1α, CXCL1, and IL-8) to attract immune cells to the site of inflammation.
Next, the researchers examined whether the coronavirus could infect the tonsils. The organoids contained key proteins required for SARS-CoV-2 infection: the ACE2 receptor, as well as the enzymes TMPRSS2 and furin. Following exposure, SARS-CoV-2 actively replicated within the organoid cells and was released into the surrounding environment. Electron microscopy confirmed the presence of mature viral particles on the cell surface 72 hours after infection.
SARS-CoV-2 not only successfully entered the tonsils but also altered their function. The virus modified lipid metabolism and iron transport while simultaneously suppressing hundreds of innate immunity genes. These changes created a favorable environment for SARS-CoV-2 replication.
More details can be found in the article “Tonsils May Serve as a Potential Reservoir for Coronavirus,” published in Biomaterials. - Individuals who have undergone tonsillectomy may have had increased exposure to various coronaviruses, common causes of upper respiratory tract infections, before and after surgery. This exposure could have led to long-term cross-immunity against COVID-19.
- Sleep apnea is linked to a higher risk of severe COVID-19. Tonsillectomy, which is often recommended for children with sleep apnea, may protect them from severe COVID-19 later in life.
The findings of this study apply only to unvaccinated populations and early SARS-CoV-2 variants. Further research is needed to determine whether similar results apply to new variants and vaccinated individuals.
Conclusion
Surgical removal of tonsils, both alone and in combination with adenoidectomy, is associated with a lower risk of both mild and severe COVID-19. This effect is unlikely to be related to inflammatory, lipid, or metabolic biomarkers in the blood.
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