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INTRODUCTION
On March 11, 2020, the World Health Organization (WHO) raised the level of contamination of the new coronavirus to the pandemic due to the rapid and uncontrollable spread of viruses, causing all health organisations in all countries of the world to adopt sanitary and protective measures to contain the progress and spread of COVID-19 (WHO, 2020a).
Since the beginning of the pandemic, several research studies have been carried out to elucidate the epidemiological and clinical issues of COVID-19, with some theories being raised about the clinical course and risk factors associated with COVID-19. Scientific evidence on the current epidemiological aspects of the disease reports that clinical conditions such as hypertension, respiratory, cardiovascular, metabolic and immunological diseases, in addition to advanced age, are classified as important risk factors for the severity of COVID-19 (Huang et al., 2020; WHO, 2020a; Yang et al., 2020).
Thus, the lack of specific preventive or therapeutic measures for the new coronavirus, coupled with its high rate of transmission and contamination, caused several government officials and WHO (2020b) to recommend the adoption of non-pharmacological interventions (INF) for the initial fight against COVID-19, such as individual and collective health security measures, among which we highlight the social restriction, with some public authorities even decreeing a total (lockdown), which drastically altered the lifestyle of all populations in the world (Garcia & Duarte, 2020).
Among the changes in the population's lifestyle caused by social restriction, we can highlight the emergence of emotional problems such as stress and/or depression, excessive use of alcohol or tobacco, reduction in the population's level of physical exercise and increased behaviour sedentary, leading to body weight gain and possible emergence of comorbidities associated with increased cardiovascular risk, such as obesity, increased blood pressure, glucose intolerance, as risk factors for the appearance of comorbidities, which increase the risk of developing the form most severe disease of COVID-19 (García Álvarez, Saiz Martínez, García-Portilla González, & Bobes, 2020; Peçanha, Goessler, Roschel, & Gualano, 2020).
However, being a new disease, there are still gaps in the scientific literature correlating the effects of physical exercise and vaccination against COVID-19. Thus, the present study proposes the following question: What is the impact of regular physical exercise on the effects of vaccination and disease control?
So, the primary objective is to elucidate, through a theoretical health essay, the related scientific evidence on how physical exercise can potentiate the effects of vaccines.
METHODOLOGY
Methodological design
The study in question is a theoretical health essay with a qualitative approach, aiming to bring a discussion, a new perspective and insights on issues of current interest (Magna, 2014).
The study was conducted in accordance with the guidelines of the Committee on Publication Ethics (COPE, 2022), which contains information on research ethics for authors and editors.
Formulation of the research question
To guide the retrieval of information, the research question was structured in order to guarantee not only the internal validity but also the extrapolation power of the results of the theoretical test since the scientific evidence of safety and efficacy are applicable between populations in different regions of the world and through the selection of studies comprehensively and exhaustively, through the adoption of criteria and evaluation of the quality and validity of the studies retrieved in the searches (Brasil, 2012).
Definition of eligibility criteria
The inclusion and exclusion criteria for selecting documents are detailed in Table 1.
Table 1 Description of inclusion and exclusion criteria for selection of studies.
| Inclusion | Studies in Portuguese, Spanish and English of the type were included: randomised clinical trials and clinical studies that evaluated related scientific evidence on how physical exercise can potentiate the effects of vaccines. |
| Exclusion | Publications that do not deal with the research object in question, studies with animals, studies that did not have published results, as well as studies that did not mention the conflict of interests were excluded. |
Selection of studies
The terms and interterms were defined from consultations by the exchanged index in the DeCS, from which the descriptors in Portuguese and their respective MeSH were extracted, submitted to later research to identify their interterms in the MEDLINE databases via PubMed portal, Embase, Cochrane Library and Scopus. The search for the definition of these terms and terms was carried out in April 2022.
Strategies were listed to guide the identification and screening of studies. First, the research period was defined between January 2020 and April 2022. Second, the electronic search will be carried out in the following databases: MEDLINE via PubMed portal, Embase, Cochrane Library, and Scopus. This choice was made in order to ensure greater coverage of peer-reviewed articles (Prayag & Ozanne, 2018) and because they contemplate a variety of journals with higher impact factors.
The chosen keywords were ‘Physical Exercise’, ‘Vaccine’, ‘COVID-19’, and ‘Coronavirus’, using the Boolean operators AND/OR, as well as their synonyms, having as search scope the respective terms in the title, abstract and words of articles published in journals. This choice is due to a previous evaluation in the literature, in which the correlation between them and the frequency with which they are used in studies was verified.
RESULTS
Therefore, the results presented by the theoretical essay in question propose a discussion based on scientific evidence, aiming to elucidate the immunological effects of regular physical exercise and its action with vaccines and, therefore, serve as a basis for future research on the subject, since there are still epidemiological and clinical gaps on how physical exercise may or may not potentiate the effects of vaccination against COVID-19.
DISCUSSION
Thus, we chose to section the discussion of the theoretical essay addressing the following topics: Physical Exercise and Immunosafety and the relationship between physical exercise and vaccination.
Physical exercise and immunosecurity
According to Cortez et al. (2020) and Nogueira, Cortez, de Oliveira Leal, and Dantas (2021), regular practice of physical exercise by the population is important due to its prophylactic and therapeutic effects on the health and quality of life of the population, increasing the responses of the immune system, contributing to the reduction of inflammation and the risk of infection.
These prophylactic and therapeutic effects are possible since each session of moderate exercise promotes a transient increase in immunosafety. When repeated for weeks or months, it promotes a systemic and tissue anti-inflammatory effect through a chronic adaptation of the organism. Studies by Duggal, Niemiro, Harridge, Simpson, and Lord (2019), Soltani, Marandi, Kazemi and Esmaeil (2020), and Wang, Li, Lu, and Huang (2020) scientifically evidence that physical exercise promotes a potent anti-inflammatory effect, decreasing inflammation in several comorbidities such as diabetes, hypertension, obesity and ageing, which are risk factors in the disease of COVID-19. These prophylactic and therapeutic effects of physical exercise have great implications for protection against COVID-19 since most fatal cases occur in populations with these comorbidities and with the elderly (Nikolich-Zugich et al., 2020).
In the case of the elderly, it is emphasised that the immune response to the virus depends on factors such as genetics, physical state and age itself, the main input receptor being the angiotensin-converting enzyme 2, with physical exercises acting as a modulator of the immune system, since during and after physical exercise, pro and anti-inflammatory cytokines are released, IL-2, IL-6, IL-7, IL-10, G-CSF, IP-10, MCP-1, MIP-1A e TNF-α, which increase lymphocyte circulation and also cellular recruitment. Such practice has an effect on the lower incidence, intensity of symptoms and mortality from viral infections observed in people who exercise regularly, and its correct execution must be considered to avoid damage (da Silveira et al., 2021).
Despite the lack of accurate data on how physical exercise improves the immune response against the new coronavirus, there is evidence such as that by Grande, Keogh, Silva, and Scott (2020) of lower incidence rates of acute respiratory infections (ARI), duration and intensity of symptoms, and risk of mortality from infectious respiratory diseases in individuals who exercise at appropriate levels, with moderate intensity (Nogueira et al., 2021). Furthermore, different studies suggest that regular exercise is directly related to decreased mortality from pneumonia and influenza, improvements in cardiorespiratory function, vaccine response, glucose, lipid and insulin metabolism, in this specific case, providing greater immunological and metabolic support for people's health obese and with metabolic diseases (Laddu, Lavie, Phillips, & Arena, 2021, Simpson & Katsanis, 2020).
For Duggal et al. (2019), an active lifestyle prevents possible changes in the immune response (decreased, unchanged or even increased) by various organic mechanisms, as shown in Figure 1. Immune reactions show an increase in lymphocyte β2-adrenergic receptors, which will allow relocation of these cells mediated by catecholamines of natural killer (NK) cells and virus-specific T cells between blood and tissues at each physical exercise session.
Source: Valenzuela et al. (2021).
Figure 1 Potential mechanisms explaining the benefits of regular - and potentially acute - exercise performed before vaccination to enhance the immune response.
Also, according to the author mentioned above, Duggal et al. (2019), it is important to emphasise that at each physical exercise session, there is a redistribution of NK cells and T cells specific to the virus, thus increasing the immunovigilance that will decrease the frequency of latent viral reactivation, reducing the antigenic capacity deposited in T cell compartments, as well as preventing the accumulation of ‘senescent’ T cells, maintaining the number and variety of naive peripheral T cells.
Scientific evidence, Cao Dinh et al. (2019) and Merellano-Navarro et al. (2021) point out that physically active older people have fewer ‘senescent’ T cells and more ‘naive’ T cells compared to sedentary people of the same age. In this sense, cytokines such as interleukin 7 (IL-7) will have their immunological activities increased, producing antigen-specific naive T cells, essential in mounting immune responses to new antigens and differentiating into ‘memory’ T cells for long-term immunity and, in the case of interleukin 5 (IL-5) they will maintain peripheral T and NK cell compartments, in order to ensure that they proliferate and function optimally when encountering virus-infected cells.
Thus, with the organic adaptations generated by physical exercise, we can have a reduction in the effects of immunosenescence, which deals with the decline of immune function and the consequent increase in susceptibility to infections, in addition to a reduction in the vaccine response, which may help to improve immune responses as a result of vaccination, maintaining the pool of peripheral T cells and their ability to respond to new vaccine antigens (Valenzuela, Simpson, Castillo-García, & Lucia, 2021). As shown in Figure 1.
In a systematic review and meta-analysis study carried out by Xu et al. (2020) on the scientific evidence for the treatment of COVID-19 through physical exercise, presented in their discussion that regular and guided exercise acts significantly in increasing the body's immune capacity, in addition to reducing the probability of infection by diseases infectious/viral, acting in a prophylactic and therapeutic way to combat COVID-19 (Barrett et al., 2012; Simpson, Kunz, Agha, & Graff, 2015).
Other meta-analytic evidence carried out by Chaabene et al. (2021) on the beneficial effects of physical exercise on the improvement of physical fitness components in the elderly, with relevance to COVID-19, highlighted the importance of regular and guided physical exercise practice by the elderly, acting significantly against the deleterious effects of physical inactivity on the health and quality of life of this population. In this regard (WHO) (2020b) launched a campaign "be active at home during the COVID-19 outbreak" to encourage people, especially older adults, to remain physically active.
Thus, physical exercise has been related to increased immune surveillance against infections, in addition to being responsible for improving the immune response. When physical exercise is performed with moderate volume and intensity, the immune system responds quickly to the physiological stress caused by physical exercise through its acute and chronic effects, acting, among others, on the effects of immunosenescence. Physical exercise is responsible for providing an increase in the antipathogenic activity of macrophages, while elevations in the circulation of immune cells, immunoglobulins and anti-inflammatory cytokines occur, thus reducing the burden of the pathogen on organs such as the lung and the risk of lung damage due to the influx of inflammatory cells (Nieman & Wentz, 2019).
Physical exercise and vaccine
A study by Pawelec and McElhaney (2020) on "Recent Advances in Influenza Vaccines" reports the efforts of researchers to improve the effectiveness of vaccines against different types of influenza, as well as COVID-19, including the development of universal vaccines independent of the circulating strains in any season of the year and the stimulation of cellular and humoral responses, especially in the elderly, showing in their results improved cellular and humoral responses in physically active people, emphasising that physical exercise and general fitness can be crucial in the increase immunological capacity and efficacy in the effect of vaccines (Ledo et al., 2020).
According to Campbell and Turner (2018), with the increase in research on the effects of physical exercise on the action of vaccines, it can provide positive effects to prevent clinically important diseases, such as COVID-19. According to Laddu et al. (2021), there is already a consensus in the literature on the positive immunological effects of the regular practice of physical exercise in the reduction of health problems resulting from transmissible diseases. Another important data on the immunological effects of physical exercise on health is that it can increase immunity after vaccination, with aerobic exercise of moderate intensity, respecting the principles of training, showing positive effects on the immune responses to the vaccine against influenza and pneumonia in adults and the elderly (Song et al., 2020).
Based on current information, there is a consensus in the literature that the regular practice of physical exercise acts significantly in increasing the autoimmune system and resistance against viral infections of the respiratory tract, such as COVID-19, since, combined with a healthy lifestyle, physical exercise can act, enhancing the immunological effects generated by the COVID-19 vaccination (Li, 2020; Luzi & Radaelli, 2020). In addition, a recent publication suggested that regular physical activity can have an important influence on the effect of the vaccine against COVID-19, both concerning the duration and magnitude of immunisation (Pitanga, Pitanga, & Beck, 2020). According to the results of the study by Gualano et al. (2021), which aimed to investigate the association between physical activity and persistent anti-SARS-CoV-2 antibodies 6 months after the schedule of two doses of CoronaVac in patients with autoimmune rheumatic diseases (ARD), identified that, among patients In immunocompromised patients, being physically active was associated with an increase in antibody persistence over 6 months after a full course of an inactivated SARS-CoV-2 vaccine.
However, although studies of randomised clinical trials with the different types of vaccines against COVID-19 have not been carried out, there is already scientific evidence from previous vaccination programs, such as influenza and flu, pointing out that regular exercise can be an effective strategy in strengthening the immune system as well as increasing antibody responses after vaccination.
CONCLUSIONS
Therefore, according to the evidence presented here, we understand that the regular and guided practice of physical exercises, respecting the principles of sports training, act significantly as an auxiliary tool in strengthening and preparing the immune system against the harmful effects COVID-19 has on health, as well as the effectiveness of the effect of vaccines against types of influenza, especially for risk groups, such as people with advanced age, hypertension, diabetes, obesity, heart and chronic respiratory diseases.
It is important to emphasise that only with vaccination can we fight the contagion, spread and COVID-19 health problems, emphasising that in addition to the regular practice of physical exercise, it is important to adhere to other preventive measures, such as good habits of life, social distancing, mask use and good hygiene, being important allies in the effectiveness of vaccines, especially for risk groups.
