The role of ozone therapy in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19): a review

Biyan Nathanael Harapan¹, Triswan Harapan^2
1 University Hospital of Munich, Ludwig-Maximilians-University of Munich (LMU), Munich, Germany
² Complementary Cardiovascular Clinic (CCV Clinic), Tangerang Selatan, Indonesia

Correspondence Address:
Biyan Nathanael Harapan,
University Hospital of Munich, Ludwig-Maximilians-University of Munich (LMU), Munich
Germany

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2045-9912.369237

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has rapidly swept across the world. As new knowledge regarding treatment options for COVID-19 has emerged, the use of ozone therapy in the context of SARS-CoV-2 infection as an integrative therapeutic option supplementary to standard treatment regimen has been assessed in the present literature. We reviewed, critically analyzed, and summarized all present published literature on ozone therapy in association with COVID-19 via the PubMed database. Various reports and studies on the use of ozone (major autohemotherapy, rectal ozone insufflation, ozone inhalation) in patients affected by COVID-19 indicate that ozone therapy may reduce morbidity and accelerate recovery, while exhibiting a high safety profile with no relevant adverse effects. Current literature suggests that integrating ozone therapy into the existing standard of care and best available therapy for the treatment of COVID-19 patients offers major advantages in terms of superior clinical outcome parameters and amelioration of laboratory results. Further prospective studies are warranted to guide the next steps in the clinical application of ozone therapy and examine its impact on the course of COVID-19.

Keywords: antioxidant; antiviral; autohemotherapy; coronavirus; COVID-19; O₃; ozone therapy; ozone; SARS-CoV-2; SARS-CoV-2 infection

Introduction

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to a major worldwide health crisis and is an ongoing global health emergency. Several countries worldwide have experienced or are currently facing a third, fourth, or even fifth wave of COVID-19, especially with the relatively new variant of concern B.1.1.529, the Omicron variant of COVID-19. The COVID-19 pandemic has serious implications for people’s health and has evidently become a challenging world issue.

As of April 6, 2022, there are 494.6 million confirmed cases of COVID-19 globally in 225 countries/geographical regions and over 6.18 million deaths.^[1] Among all closed cases, 430.2 million subjects have recovered throughout the world, pointing to a recovery rate of around 99%.^[1]

While respiratory symptoms are common for COVID-19, various other manifestations have been recognized. Furthermore, since many complications might arise from SARS-CoV-2 infection,^[2],[3] identifying potential risk factors, early diagnosis and prompt initiation of treatment are crucial when dealing with COVID-19.

Considering the limited therapeutical options currently available, the evaluation of novel therapeutic resources against COVID-19 represents a priority in clinical research. No established therapy exists; therapeutic options include supportive therapies (e.g., heparin, steroids), antiviral (e.g., remdesivir, tocilizumab) or immunomodulatory treatment (e.g., hyperimmune plasma).

Despite the use of ozone therapy worldwide, orthodox medicine has not fully taken advantage of the many benefits of ozone therapy. This review aims to outline the current knowledge on ozone therapy in COVID-19 patients.

Methods

We searched the PubMed database for articles in English, German or Spanish published until March 14, 2022. Different key words related to ozone therapy and COVID-19 in titles and abstracts were used (“COVID-19,” “SARS-CoV-2,” “corona-virus,” “ozone therapy,” “ozone,” “O₃” and “medical ozone”). All relevant publications were independently screened by both authors (BNH and TH) in their entirety to determine eligibility for inclusion. Apart from published studies with a conclusive outcome, review articles, case reports, case series, editorials, commentaries, and other articles were considered in this review to fully exploit the potential offered by current literature and maximize comprehensiveness. Due to the small amount of available data, all studies that assessed the effects of ozone therapy on COVID-19 patients were evaluated regard-less of study designs. Exclusion was mainly based on topic, for instance, if the full text article did not primarily focus on ozone therapy and COVID-19. Unpublished articles were not retrieved. Results of selected articles are reported in a narrative manner and divided into different sections within the text of this review, while the main findings of relevant studies and articles are summarized in tables.

Results

Ozone therapy

Biochemical and pharmacological aspects of ozone

Ozone is a natural bioactive molecule with antioxidant proper-ties. It is a triatomic gaseous inorganic molecule that is found in nature and generated by lightning and solar ultraviolet radiation. Its chemical formula is O₃. Ozone is highly soluble in water and decomposes spontaneously and rapidly, breaking down into O₂ and O^-. The great solubility of O₃ in water is responsible for the immediate reaction with various soluble compounds and biomolecules existing in biological fluids. Due to its high reactivity, ozone also reacts with various bio-molecules when dissolved in plasma.^[4],[5]

Routes of ozone administration

There are several ozone administration routes that can be chosen, depending on treatment goals and location of therapy. The route of administration ranges from systemic or locoregional administration of ozone mixtures to topical application of ozonated derivatives. For instance, ozone can be administered systemically/intravenously (e.g., via autohemotherapy with ex-tra-corporeal blood-ozone mixture), intramuscular, into body cavities (e.g., rectum via rectal insufflation), intraperitoneally via intraperitoneal insufflation, intra-articular, subcutaneously and into soft tissues, myofascial, intradiscally, intratumorally and even intrathecally.^[6],[7]

One of the most common application methods is O₃ major autohemotherapy (MAH), where a blood sample (usually 100–200 mL) is obtained and subjected to a precise concentration of O₂/O₃ ex-vivo. After O₂/O₃ infusion, the blood sample is then administered to the patients.

Adverse reactions, complications, and contraindications of ozone therapy

Ozone therapy essentially does not exhibit adverse or toxic effects when performed properly. This is also confirmed by the studies mentioned in our review article. Ozone allergic reactions or allergic-like intolerance have not yet been reported.^[8] Generally, the incidence of side effects of ozone therapy seems to be very low, while euphoria, nausea, headaches and fatigue are common manifestations.^[9],[10]

In a different context other than MAH and rectal ozone insufflation, adverse reactions of ozone therapy have been identified. For instance, if direct intravenous administration is chosen as a delivery route due to difficult vein conditions that exclude the possibility of MAH, ozone can irritate veins, depending on the ozone concentration. Ultimately, direct intravenous administration bears the risk of vein sclerosis despite its clear advantages in cost and ease of administration.^[11] Temporary chest tightness and cough have also been observed.^[11],[12]

Only very few serious complications have been described so far, e.g., a suspected pulmonary embolism after ozone therapy for low back pain.^[13] Here, the authors believe that a venous vessel was accidentally punctured during intradiscal injection which created emboli, leading to the occurrence of massive pulmonary embolism. Three other cases of gas emboli/stroke have been reported in the literature that are all associated with (intradiscal) ozone injections: a patient with chronic neck pain treated with paravertebral ozone injection, leading to multi-focal stroke,^[14] a case of vertebrobasilar stroke^[15] and finally a case of paradoxical embolism resulting in anterior spinal cord syndrome and consecutive acute myocardial infarction following intradiscal injection of ozone.^[16]

Contraindications for ozone therapy include pregnant women, patients with uncontrolled hyperthyroidism, serious cardiovascular instability, and patients with glucose-6-phos-phate dehydrogenase deficiency.^[8]

Mechanisms of action of ozone therapy in SARS-CoV-2 infection and COVID-19

The biological potency and clinical effects of ozone therapy can be – among others – traced back to the reaction of ozone with different amino acids, proteins, and unsaturated fatty acids, which are found in plasma and biological cell membranes. Some effects of ozone involve the generation of reactive oxygen species such as free radicals, superoxide, or hydroxyl radicals. These radicals are chemically reactive compounds that have significant effects at a cellular level.^[17]

In the field of oncology, ozone therapy has shown cytotoxic effects on some types of tumors related to a modification of reactive oxygen species, free radicals and antioxidants, while causing no adverse effects in normal cells due to their intact antioxidant defense system. As a consequence, ozone may be used complementary to conventional cancer treatment such as radiotherapy and chemotherapy, since data suggest that ozone therapy as adjuvant treatment might amplify anticancer effects.^[18]

Some authors propose that the therapeutic effect of ozone is associated with moderate and controlled oxidative stress. Ozone leads to the activation of a certain nuclear transcription factor, namely nuclear factor erythroid 2-related factor 2 (Nrf2).^[19] This in turn induces the transcription of antioxidant response elements followed by the production of several antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase.^[20],[21] Since oxidative stress fundamentally contributes to the development and exacerbation of COVID-19, ozone therapy may protect from a more severe course of COVID-19. Other molecular mechanisms related to anti-apoptotic and pro-autophagy processes targeted by O₃ are also associated with the Nrf2 biological pathway.

Apart from reactive oxygen species, ozone can trigger other “second messengers” known as lipid oxidation products (LOPs), which are responsible for different biological and therapeutic effects. LOPs have a longer half-life and interact with various organs after reaching the vascular system, triggering late effects. Through several biochemical steps, LOPs induce essential oxidative stress proteins, among others heme oxygenase-1, which represents a crucial antioxidant and protective enzyme.^[4] Furthermore, LOPs exhibit neuroimmunomodulatory effects via modulation of cytokines and additionally stimulate endothelial production of nitric oxide that mediates vasodilatation.^[5],[22]

Moreover, ozone improves blood circulation and perfusion of organs (e.g., the lungs) and consequently the metabolism of oxygen. Levels of adenosine triphosphate and 2,3-diphos-phoglycerate are increased in erythrocytes following ozone administration, resulting in a shift in the hemoglobin dissociation curve to the right, thereby improving oxygen supply to ischemic tissue since delivery of O₂ to the tissues is facilitated.^[5]

Present data suggest that different virus types can be inactivated when exposed to ozone. The promising results of ozone therapy in several viral infections^[23] including Ebola^[12] led to the hypothesis that ozone therapy is also effective against SARS-CoV-2. For instance, a study by Murray et al.^[24] used ozone to inactivate a variety of enveloped and non-enveloped viruses including herpes simplex virus type-1, vesicular stomatitis Indiana virus, vaccinia virus, adenovirus type-2, and a certain strain of influenza A virus. The authors concluded that ozone exposure reduced viral infectivity by lipid peroxidation and consecutive damage to the lipid envelope and protein shell.^[24]

It is known that SARS-CoV-2 has a spike protein that interacts with angiotensin-converting enzyme type 2 (ACE2) cell receptors, leading to cell invasion and infection.^[2] The virus exploits the ACE2 receptor for cell internalization. SARS-CoV-2 viral replication can therefore be impaired by blocking the activity of this receptor. A current study shows that this can be achieved via upregulation of Nrf2 biological pathway.^[25] Since ozone enables rapid Nrf2 activation (see above), endogenous SARS-CoV-2 viral replication is blocked or prevented.

Analogous to other coronaviruses, SARS-CoV-2 has essential cysteine (residues) in their spike proteins^[26],[27] that may be exploited via ozone autohemotherapy. O₃ can inactivate the spike protein by oxidation, whereby the cysteine residues are very susceptible to oxidation. The cysteine residues consist of sulfhydryl groups called thiol groups that are key elements in the mechanism of viral entry and viral membrane fusion with the host cell membrane.^[28] Upon oxidation, chemical activity of proteins is disrupted and thus, SARS-CoV-2 could potentially be inactivated by ozone-mediated oxidation during the viremic phase, altering cysteine residues and ultimately disrupting the cycle of virus replication.^[29]

[Table 1] summarizes the main effects and biological reactions of ozone therapy.

Table 1: Main effects and biological responses of ozone therapy Click here to view

Clinical utility of ozone therapy in SARS-CoV-2 infection and COVID-19

The rationale of most studies is to determine the clinical utility of complementary ozone therapy in addition to standard of care in COVID-19 patients. Many studies and reports indicate superior clinical outcome parameters and amelioration of laboratory results in COVID-19 patients when integrative ozone therapy is employed supplementary to best available therapy,^{[5],[6],[9],[30],[31],[32],[33]} which might hint at additive anti-inflammatory and immunomodulatory effects mediated by blood ozonization.

Zheng et al.^[34] performed a clinical study where two patients with confirmed severe COVID-19 were treated by ozone therapy via MAH once daily for seven consecutive days. These two cases were compared with two age- and illness severity-matched subjects who did not receive MAH. The subjects without MAH treatment exhibited longer duration of viral shedding and length of hospital stay.^[34]

In a case-control study conducted in Italy, the clinical outcomes of 30 COVID-19 patients who received ozone MAH in addition to “best available therapy” (e.g., antiretroviral therapy, antibiotics, steroids) were compared with those of 30 COVID-19 patients not treated with MAH. Not only was the clinical improvement in the group with ozone adjuvant therapy more prevalent (measured according to the different clinical phenotypes by the Italian Society of Emergency and Urgency Medicine), but the control group also had a worse outcome in terms of clinical worsening (17%) compared to the ozone group (7%). In conclusion, ozone therapy might be clinically effective in patients with mild to moderate COVID-19 pneumonia.^[6]

Ozone autohemotherapy was further employed in a study by Franzini et al.^[30] where ozone therapy revealed an improvement in COVID-19 patients’ clinical condition by ameliorating major respiratory indexes and blood gas parameters, resulting in a fast recovery from acute respiratory distress syndrome. Limitations of the study are due to the nature of this case series study, in which the homogeneity of patients (subjects were all male and older than 60 years) plays a major role.

Araimo et al.^[35] conducted an interventional, open randomized, two-arm study, comparing 14 COVID-19 patients who received MAH with a control group consisting of 14 COVID-19 patients treated with best available therapy only. Interestingly, inflammation markers, hematology profile, and lymphocyte subpopulations were all not significantly influenced by ozone therapy, indicating a limited effect of systemic O₃ administration since it further does not seem to have an impact on the progression of COVID-19 and related mortality. However, similar to previous reports and studies mentioned above, no adverse events related to the use of ozone were reported, underlining that O₃ has a high safety profile. Moreover, the results hint at a moderate reduction in the need for ventilatory support in COVID-19 patients who received ozone therapy, although not reaching statistical significance.

Of note, several authors who critically analyzed this study are of the opinion that the study by Araimo et al.^[35] was too imprecise to evaluate the role of ozone autohemotherapy in COVID-19 patients and that it discredited other positive results described in the current literature. Points of criticism include a discrepancy in primary and secondary endpoints, implementation of sample enrollment and stratification, and other statistical confounders.^[36]

The benefit of additional MAH to supportive treatment was also demonstrated in a prospective case-control study by Hernández et al.^[9] in which nine COVID-19 patients received MAH while another nine COVID-19 patients did not. It was evident that ozone autohemotherapy was linked to a significantly shorter time to clinical improvement. Previously, the authors highlighted the potential benefit of ozone treatment in a small case series with three cases of COVID-19 patients with pneumonia treated with four to six sessions of ozonated autohemotherapy, who all exhibited rapidly improved hypoxia with associated decreases in inflammatory markers and D-dimer. None of the three patients who presented with respiratory failure had to undergo invasive mechanical ventilation; early discharge on days three to four after completed autohemotherapy was possible.^[31]

Similar to many studies mentioned above, Wu et al.^[32] also showed an improvement in the expression of infection-related biomarkers (C-reactive protein (CRP), interleukin 6) in four COVID-19 patients after receiving the combination of MAH with antiretroviral therapy. Notably, a younger sibling of one of the patients was also diagnosed with COVID-19 and admitted to the same hospital on the same day. However, this patient did not receive ozonated autohemotherapy and had a significantly longer stay in hospital despite the same antiretroviral therapy. Consequently, the overall medical cost for this patient was considerably higher than for his sibling, pointing to additional possible economic advantages of ozone treatment.^[32]

The effectiveness of MAH is further underlined in a prospective quasi-experimental before-and-after study performed in India, where 37 COVID-19 patients who received MAH were compared to 18 COVID-19 patients only treated with the standard treatment regimen. Here, the authors discovered that the mortality rate was significantly lower in the ozone group than in the control group. What is more, intensive care unit (ICU) hospitalization was required in 16.2% of COVID-19 patients who were additionally treated with ozone therapy, while 22.2% of patients in the control group were ICU patients.^[33]

In order to assess whether ozone autohemotherapy can reduce fatigue symptomatology in patients suffering from post-acute sequelae of SARS-CoV-2, Tirelli et al.^[37] treated 100 patients with post-acute sequelae of SARS-CoV-2 using ozone autohemotherapy. The authors employed a Fatigue Severity Scale before and after treatment to quantify fatigue. Ozone autohemotherapy improved fatigue symptoms in all recruited patients, even though to different extents.^[37]

A randomized control trial conducted in India suggested that the combination of rectal ozone insufflation and minor ozone autohemotherapy significantly leads to clinical improvement, lower mortality, and shorter time to clearance of virus in mild to moderate COVID-19 patients.^[38] Subjects who received ozone therapy did not require supplemental oxygen and were not admitted to the ICU (also not needing mechanical ventilation), whereas 10% of the control group’s subjects required mechanical ventilation and two fatalities were additionally noted. The authors deduce that ozone therapy potentially does not only reduce mortality but can accelerate recovery in COVID-19 patients.

Case reports have shown promising results regarding the safety of rectal O₃ insufflation in COVID-19 patients with marked hypoxia.^[39] After receiving ozone therapy, a rapid improvement of oxygen saturation without side effects was recorded. These findings match with the result of a case report describing a geriatric patient with severe COVID-19 pneumonia who received rectal O₃ insufflation. The patient suffered from pre-existing medical conditions such as chronic obstructive pulmonary disease and pulmonary nodule with malignant criteria. No or minimal clinical improvement was initially noticed before ozone therapy, however, significant improvement of oxygenation was observed after rectal ozone therapy.^[40]

The role of ozone therapy as an adjunct therapeutic option in COVID-19 pneumonia is further evaluated in a small series of four COVID-19 patients with severe pneumonia. Using rectal insufflation for additional ozone therapy to standard treatment, clinical, biochemical, and radiological changes were observed in these patients. Clinical variables such as O₂ saturation and O₂ supply, biochemical variables of inflammation (leucocyte and lymphocyte count, procalcitonin, CRP, interleukin 6) and radiological variables (edema and alveolar infiltrates) all improved in each patient.^[41] The same authors were able to reproduce these results in a case-control study, where the use of rectal ozone in patients with severe COVID-19 pneumonia improved clinical, biochemical and radiological variables when compared to standard of care only.^[42]

Finally, a single prospective randomized trial on ozone therapy via ozone inhalation has shown several positive effects on COVID-19 patients.^[43] 15 COVID-19 patients were treated with “lung disinfection technique” via ozone inhalation in addition to standard treatment, while another 15 COVID-19 patients only received standard care. The authors could observe a shorter length of hospital stay in subjects treated with ozone inhalation. Besides, CRP decrease was more prevalent in COVID-19 patients additionally treated with lung disinfection technique (75% vs. 25% in the control group). Another finding is that significantly more patients had a negative PCR result after ozone treatment in comparison to those who received standard care only (93% vs. 20%), thereby hinting at a possible faster clearance of SARS-CoV-2 virus in patients treated with ozone inhalation. It should be noted that – for the ozone treatment – the authors employed a device that has never been produced before and is not available in the market. The well-known fact that ozone has toxic effects on the lungs at high doses along with the lack of standardized devices or protocols regarding ozone inhalation specifically for treating COVID-19 patients implies that the results of this study are to be viewed with utmost caution and that more studies are needed to address all these issues appropriately.

[Table 2] offers a clear overview of all published reports and studies on ozone therapy in COVID-19 patients, summarizing the publication year, country, type of study, enrolled patients, method of ozone administration, results, and key findings in one table.

Table 2: Clinical trlals/studles and reports on ozone therapy for COVID-19 patients Click here to view

Conclusions

Present reports and studies support the clinical utility and possible antiviral activity of ozone therapy in the treatment of COVID-19 patients. Overall, ozone is more likely to be considered as an antiviral drug enhancer and not an alternative to antiviral drugs, making ozone therapy as a suitable integrative therapeutic option to standard treatment regimen in patients with COVID-19. Different mechanisms of action lead to antiviral activity, e.g., through direct inactivation of viruses and inhibition of viral replication and indirect effects such as stimulation of the immune system, antioxidant and anti-inflammatory effects.

Many preliminary reports emphasize that no side effects occur when administering ozone gas in the correct dose. There are still many aspects that need to be clarified. The optimal administration form, dose, concentration, schedule, stage of the disease, patient selection, concomitant administration of antioxidants is still to be determined, especially in regard to the combination of ozone therapy with other treatment modalities to increase treatment efficacy. Specifically, these aspects need to be dealt with for the eventual use of ozone therapy in the context of COVID-19.

Furthermore, several limitations must be addressed. First, many publications presented in this review, case reports in particular, lacked a comparison/control group that can limit the validity of the study. Most studies were predominantly observational and/or retrospective studies and not randomized controlled trials, which remain the gold standard for evidence. In addition, the majority of studies include a small sample size that can undermine the internal and external validity of the study and reduces the power of the study, while increasing the margin of error. Although a clinical benefit of ozone therapy was already observed in most COVID-19 patients, a greater sample size is necessary to improve statistical significance. Thus, the interpretation of several studies presented in our review article is to a certain extent limited due to small size of the enrolled groups, the retrospective nature of studies, and the lack of randomization.

In the absence of specific treatment options, supportive therapies remain the cornerstone for treating COVID-19 patients. From the available evidence in the present literature, we conclude that integrating ozone therapy into the existing standard of care and best available therapy might reduce morbidity and accelerate recovery in COVID-19 patients.

Nonetheless, to confirm ozone therapy as a viable complementary treatment option against COVID-19, randomized controlled trials and further studies are warranted to support the promising background data and expert opinions indicating the effectiveness of ozone therapy in patients suffering from COVID-19.

Author contributions

Conceptualization, methodology, data analysis, and writing – original draft: BNH; investigation and writing – review & editing: BNH, TH; supervision: TH. Both authors read and approved the final version of this manuscript.

Conflicts of interest

Both authors state that there is no conflict of interest.

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