COVID Extremes: Most Hospitalized Patients Still Have Symptoms 6 Months Later; But Asymptomatic Cases Are Driving Transmission
Health care worker taking the temperature of an asymptomatic COVID-19 postive individual in an assisted living facility in Ohio.

Two new studies published this week highlight the challenges to health policy posed by COVID-19 – with seriously ill COVID-19 patients continuing to suffer with “Long COVID”  months after being released from the hospital – while completely asymptomatic cases drive more than half of overall disease transmission.  

More than three quarters of patients diagnosed with COVID-19 have at least one persistent symptom six months after falling ill, finds a new study published Saturday in The Lancet, the largest yet on the long-term effects of the virus.  Some 76% of over 1,700 patients studied reported experiencing at least one symptom half a year after their initial onset of symptoms and hospitalization.

The study found that fatigue or muscle weakness – the most common persistent symptom – was reported by 63% of patients, while a quarter experienced sleep difficulties, and 23% experienced anxiety or depression. 

Researchers from several universities and hospitals in China, including the Jin Yin-tan Hospital in Wuhan and the China-Japan Friendship Hospital in Beijing, examined 1,733 patients discharged from the Jin Yin-tan Hospital with COVID-19. The follow-up study, conducted between June and September, contains the longest follow-up period of a peer-reviewed study on the long term effects of SARS-CoV2 infection. 

“Our analysis indicates that most patients continue to live with at least some of the effects of the virus after leaving the hospital, and highlights a need for post-discharge care, particularly for those who experience severe infections,” said Bin Cao, vice-director of the National Clinical Research Center for Respiratory Diseases and co-author of the study. 

According to the study’s scale of disease severity, the risk of reporting at least one symptom was higher among those hospitalized and requiring ventilation than those hospitalized but not requiring supplemental oxygen. 

Doctor checking on a COVID-19 patient connected to a ventilator in the ICU in Louisiana.

Those higher on the disease severity scale were found to have more problems with mobility, pain and discomfort, as well as reduced lung function – characterized by decreased flow of oxygen from the lungs to the bloodstream – compared to those with a less critical COVID-19 infection. 

Diminished exercise capacity was noted among patients with more severe disease, with 29% of those high on the severity scale walking less in six minutes than the lower limit of the normal range, compared with 24% at the lower end of the scale. 

Age and gender were also risk factors for symptoms. Older age was associated with higher levels of lung diffusion impairment and fatigue or muscle weakness, while being a woman was a risk factor for persistent psychological symptoms, such as higher levels of stress, anxiety and depression. 

The results of the study are consistent with previous data gathered on long term SARS symptoms. In a study from 2007, 33% of patients reported significant reductions in mental health and 18% had lowered exercise capacity a year after their illness. A four year follow-up study found that 40% of patients still had a chronic fatigue problem, along with other psychiatric morbidities.  

Beyond influencing mental health and lung function, COVID-19 has also been linked to adverse impacts on other organs. Approximately 13% of patients with normal kidney function at the time of their hospitalization with COVID-19 had lower levels of kidney function at the follow-up. 

Additionally, six months after COVID-19 infection, the levels of neutralizing antibodies were 52% lower than at the time of infection. The authors warn of the potential implication for re-infection. 

“Our work also underscores the importance of conducting longer follow-up studies in larger populations in order to understand the full spectrum of effects that COVID-19 can have on people,” Bin Cao said. 

COVID-19 Infections Driven By Asymptomatic Carriers

Paradoxically, however, while some people suffer serious long-term impacts, it is asymptompatic individuals who are responsible for more than one-half of all SARS-CoV-2 transmission, according to another study published in the Journal of the American Medical Association on Thursday.

The study reported on the results of a model, developed by the US Centers for Disease Control (CDC), which found that 59% of transmission of SARS-CoV-2 is caused by asymptomatic carriers.

“The bottom line is controlling the COVID-19 pandemic really is going to require controlling the silent pandemic of transmission from persons without symptoms,” Jay Butler, deputy director for infectious diseases at the CDC and co-author of the study, said in an interview with the Washington Post

The analytical model is based on a series of assumptions about peak infectiousness, the proportion of individuals that never develop symptoms, and the infectiousness of presymptomatic or asymptomatic individuals. 

The proportion of transmission due to all individuals without symptoms at the time of transmission. For example, peak infectiousness at the same time as median symptom onset (0 days difference) with 10% of transmission from individuals who never have symptoms would mean that approximately 51% of transmission is from asymptomatic individuals.

According to authors of the study, under a range of scenarios and assumptions, the model consistently indicated that at least 50% of transmission is linked to individuals without symptoms at the time of transmission. 

The baseline scenario assumed that asymptomatic individuals are 75% as contagious as those who develop symptoms and established that 35% of asymptomatic transmission originated from presymptomatic individuals and 24% from those who never develop symptoms. 

These findings highlight the importance of wearing masks, hand hygiene, social distancing, and strategic testing in order to slow the spread of COVID-19. 

“The community mitigation tools that we have need to be utilized broadly to be able to slow the spread of SARS-CoV2 from all infected persons, at least until we have those vaccines widely available,” said Butler.

Although the model simplifies the complex phenomenon of transmission and makes several assumptions, the findings could assist in beginning to understand and control asymptomatic transmission. 

This is particularly important in the context of the global spread of two more contagious variants of SARS-CoV2. 

Image Credits: Flickr – The National Guard, Flickr – US Navy, JAMA.

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