It is difficult to confirm the actual number of omicron infections.
The infection rate of omicron in this study is 71.86%, which may be lower than the actual value. The reason for this result may be that the criteria for diagnosing infection are not uniform. Due to the adjustments made by the Chinese government to the prevention and control policies for COVID 19 and the lack of actual medical resources, it has not been possible to ensure that everyone has been tested for SARS-CoV-2 nucleic acid to confirm whether they are infected. Therefore, in this study, only 17.3% of the respondents identified their own infection by testing nucleic acids, 29.09% of the respondents identified their own infection by testing the SARS-CoV-2 antigen detection kit, and 53.61% of the respondents identified their own clinical symptoms. Some residents have not undergone any diagnostic test because they have no symptoms, but that does not mean they have not been infected with the SARS virus. Nowadays, the number of infections can only be estimated through various big data methods. It is very difficult to find out the actual number of people who have been infected.
The symptoms of the infected person are relatively mild.
COVID-19 is a self-limiting disease. Therefore, most patients have mild symptoms and can recover on their own. There is no age or gender difference in the SARS-CoV-2 infection, but the clinical symptoms are related to age. Children infected with SARS-CoV-2 have fewer symptoms than adults, and elderly people over 60, even without other underlying diseases, have more severe symptoms than young people[3]. The subjects of this study were residents aged 10 to 60 years, with an average age of 35.2 years. Most of these people subjectively feel that their symptoms are not serious, with 16.54% feeling that their symptoms are relatively serious, and 1.71% feeling very serious. In the survey results of 72314 cases reported in China in 2020, 81% were mild patients, 14% were severe patients, and 5% were critically ill patients[3]. During the more than three years of the global pandemic of COVID-19, the continuous mutation of SARS-CoV-2 has also weakened its toxicity. The prevalence of severe illness caused by the currently prevalent omicron strain is extremely low[2].
Among the various symptoms of COVID-19, fever is the most common and closely related to the occurrence of other symptoms. After infection with SARS-CoV-2, a series of pathological changes occur due to persistent lung, nerve, and cardiac tissue damage, as well as viral load mediated inflammation and immune disorders[4]. SARS-CoV-2 binds to ACE2 and enters host cells to extensively attack tissues and organs, triggering a systemic inflammatory state[5], which is the cause of systemic high fever in the body. Although the occurrence of fever makes patients feel very uncomfortable, the fever generally does not last long and fluctuates within a certain range, and most patients can recover within 3 days.
Sleep disorders are associated with COVID-19 symptoms
There is a reciprocal relationship between sleep quality and the occurrence of diseases. Insufficient sleep can have a negative impact on immunity and increase the risk of illness. In addition, inflammation levels are positively correlated with depressive symptoms, which can lead to sleep disorders[6]. What’s more, the increasing cases of COVID-19 make people more anxious and worried about health issues, and these negative emotions can further affect sleep quality. In a study involving 182 COVID-19 patients, 64.8% of them experienced insufficient sleep[7]. In our study, 77.19% of patients with COVID-19 experienced sleep disorders, but the symptoms were not limited to insufficient sleep. We further analyzed the causes of sleep disorders in these patients and found that fever was the most common factor. Patients with high fever were often accompanied by headaches, sweating, and muscle soreness, while changes in external ambient temperature further stimulate the body's temperature sensing system, making people feel very uncomfortable. Therefore, the most typical symptom of sleep disorders is pain and discomfort during sleep that affects sleep. Moreover, these symptoms change repeatedly over a period of time, so people may also wake up from sleep with the recurrence of symptoms.
Loss of appetite is the main symptom of the digestive system
The digestive system symptoms of COVID-19 patients are mainly nausea, vomiting, loss of appetite, diarrhea, and so on. However, in this study, patients with digestive system symptoms mainly manifested as loss of appetite, while other symptoms occurred less frequently. First of all, when you have a fever, the activity of various digestive enzymes will also be affected to a certain extent due to the increase in body temperature, so there will be a phenomenon of loss of appetite. There are also a small number of patients who experienced the loss of sense of smell and taste, and this neurological symptom may also affect appetite. secondly, due to the widespread distribution of ACE2 in the gastrointestinal tract such as the small intestine and colon, SARS-CoV-2 attacks the digestive system and causes gastrointestinal symptoms such as diarrhea, nausea, vomiting, and loss of appetite[8]. What’s more, intestinal ACE2 is involved in regulating the expression of neutral amino acid transporters, and intestinal SARS-CoV-2 may affect tryptophan absorption through ACE2, leading to a decrease in antimicrobial peptides, thereby altering intestinal flora and ultimately leading to intestinal inflammation[9], which may be the main cause of diarrhea. In general, symptoms of the digestive system are generally mild and gradually recover as other symptoms.
Fatigue will continue for a period of time after the acute phase.
During COVID-19 rehabilitation, fatigue is common among patients, but changes in physical fatigue are dominant, while changes in mental fatigue are not significant. Through a 6-month follow-up study, researchers have found that 63% of infected people are experiencing physical fatigue or muscle weakness, while 26% of infected people have breathing difficulties, which seriously restrict people's participation in daily activities[10]. In another 7-month follow-up study, 45% of patients needed to reduce their working hours compared to before their illness, and 22.3% of patients did not work due to illness[11]. The decline in the level of physical activity after infection with SARS-CoV-2 has been confirmed by many studies. SARS-CoV-2 may cause dysfunction of various systems through extensive attacks on the respiratory system, circulatory system, motor system, and nervous system, thereby reducing the body's motor ability under the combined effects of various systems. Therefore, we believe that the main body fatigue caused by infection with Omicron is peripheral body fatigue. This fatigue is manifested in patients who clearly feel physically inadequate, need more rest, feel sleepy during the day, and feel laborious while performing household chores or learning tasks. Recovery from fatigue requires a certain period of time, and the length of time varies from person to person. Most patients in our study generally need 1 to 2 months to recover, but other studies have shown that some even require 6 months or longer.
The symptoms of skeletal muscle are a characteristic of COVID-19
After infection with SARS-CoV-2, most patients have obvious symptoms related to skeletal muscle such as muscle pain and muscle weakness[12], which gradually turn into chronic symptoms such as muscle fatigue and exercise intolerance after the acute phase. In a meta-analysis of 3062 subjects, it was found that among symptomatic COVID-19 patients, myalgia and fatigue were the third most common symptoms after persistent fever and cough[13]. The effects of COVID-19 on skeletal muscle function are mainly manifested in aspects such as decreased skeletal muscle quality, impaired skeletal muscle metabolism, and structural damage to muscle fibers. It’s the main reason of muscle pain that inflammatory reactions and cytokine storms caused by infection with SARS-CoV-2. Muscle fiber damage and pain responses are typical symptoms of inflammatory reactions in the body[14]. Decreased skeletal muscle strength and muscle pain are important factors that cause physical fatigue in patients. In this study, most patients with weakness and muscle pain are associated with fatigue .
The scientific movement can prevent the occurrence and development of COVID-19
Scientific and regular participation in sports can induce good adaptive changes in the immune system. This behavior can not only enhance the activity of immune cells, but also enhance the activity of anti-inflammatory cytokines and reduce the activity of pro-inflammatory cytokines[15]. Therefore, exercise can effectively improve the body's immunity and reduce inflammatory reactions. In a survey of 48440 infected individuals, it was found that the lack of physical activity was highly correlated with the risk of severe COVID-19 infection[16]. People with good cardiopulmonary function and health levels can reduce the severity of post infection diseases[17]. Therefore, people participating in regular sports can effectively resist viral respiratory infections and improve lung disease[15].
However, after infection with SARS-CoV-2, people cannot blindly participate in sports during recovery to avoid worsening the condition. According to actual reported cases, some patients started exercising after experiencing a series of symptoms of COVID-19, but their condition recurred after participating in long-term bicycle riding exercise[18]. The reason for this situation may be that the immune cell function of the body is inhibited after acute, prolonged, and intense exercise. This is mainly manifested in a decrease in the cytotoxic effect of natural killer cells in the blood, impaired neutrophil function, and a decrease in the count of lymphocytes and monocytes. These changes cause a temporary decline in immunity, which may once again give SARS-CoV-2 occupy an attacking advantage in the body. The functions of various organs and systems in the body have not yet fully recovered after the acute phase of COVID-19. Therefore, we should gradually increase the length and intensity of physical activity, and strengthen monitoring of exercise responses.