A new study conducted by researchers at University Hospital Münster suggests that previous infection with seasonal coronaviruses may protect against critical cases of coronavirus disease 2019 (COVID-19).
Seasonal coronaviruses, which generally cause mild respiratory illness and symptoms of the common cold, belong to the same viral family as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – the agent that causes COVID-19.
Intriguingly, Joachim Kühn and colleagues found that patients with critical cases of COVID-19 had significantly lower levels of antibodies against seasonal coronaviruses than patients who had less severe disease.
More specifically, levels of immunoglobulin G (IgG) antibodies against the human coronaviruses (HCoVs) OC43 and HKU1 were significantly lower among COVID-19 patients with critical disease than among those with moderate-to-severe or mild disease.
The researchers say this finding should be validated in other settings and could identify high-risk individuals before they become infected.
Identifying such individuals is a priority during this stage of the pandemic to help guide protective measures and vaccination strategies says the team.
A pre-print version of the paper is available in the server medRxiv* while the article undergoes peer review.
Proportion of ordinal HCoV antibody levels from COVID-19 patients with and without critical disease. a) OC43 (p=0.016) b) HKU1 (p=0.023) c) 229E (p=0.30) d) NL63 (p=0.82). COVID-19 patients with critical disease present low antibody levels more frequently than patients without critical disease. This difference is significant for OC43 and HKU1.
Clinical course of COVID-19 is highly variable
The clinical course of COVID-19 is highly variable between individuals. While the majority of patients develop mild disease that can be managed in the outpatient setting, 10 to 20% require hospitalization and around 5% require admission to intensive care units, where the fatality rate is high.
Known risk factors for more severe disease include older age, male gender, high body mass index, and comorbidity. However, young and apparently healthy individuals can also die from COVID-19, and the variability in the disease course is not well understood.
Recently, a survey found that patients who experienced mild COVID-19 symptoms reported having frequent contact with small children, potentially suggesting that exposure to common childhood infections might reduce the severity of the disease.
“This corresponds to the low incidence of severe COVID-19 infections in small children,” writes Kühn and colleagues.
Furthermore, some studies have recently reported immunological cross-reactivity against SARS-CoV-2 among individuals who have not been exposed to the virus.
Where do seasonal coronaviruses come in?
Seasonal coronaviruses such as the human coronaviruses (HCoVs) 229E, NL63, OC43, and HKU1, which frequently infect children, generally only cause mild respiratory illness and symptoms of the common cold.
These pathogens belong to a subfamily of viruses called orthocoronavirinae – the same group that SARS-CoV-2 belongs to.
“From a public health perspective, the relatively high proportion of COVID-19 patients with critical disease poses the key problem of this pandemic: overload of the healthcare system,” said Kühn and team.
If it is the case that previous infection with a known pathogen could modify the course of COVID-19 and therefore reduce the need for intensive care, this could become an important step in fighting the pandemic.
People at risk for severe disease could be identified before they become infected, and appropriate protective measures could be taken.
“Of note, this might also be relevant for vaccination strategies,” added the researchers.
Testing the association in hospital inpatients and outpatients
The team conducted an observational study to assess whether previous infection with seasonal coronaviruses (as measured by antibody levels) may be associated with the severity of COVID-19.
Serum samples were taken from 60 patients, aged a median of 58 years (age range 30 to 82), with RT-qPCR-confirmed COVID-19 infection. Fifty-two of the participants were male, and eight were female.
Nineteen of the participants were inpatients who required critical care (ICU group); 16 were inpatients who had severe or moderate disease (non-ICU group), and 25 were patients with disease that could be managed in the outpatient setting.
What did the team find?
The study found that elevated levels of HCoV OC43 and HCoV HKU1 antibodies were associated with less need for intensive care therapy.
Patients in the ICU group had significantly lower levels of IgG antibodies against HCoV OC43 and HCoV HKU1, compared with all other patients.
The team also observed a trend towards reduced length of hospital stay among those with higher levels of these antibodies.
Long hospital stays were predominantly observed among patients with low levels of the antibodies, although this correlation was not significant.
What did the authors conclude?
“Our results indicate that previous infections with seasonal coronaviruses might protect against a severe course of disease,” said Kühn and colleagues.
The researchers propose that previous exposure to seasonal coronaviruses might facilitate immune responses to SARS-CoV-2 but say further studies are needed to assess the molecular mechanism underlying the findings.
Further studies should also be conducted to validate the findings and to explore the potential to identify people at risk for severe disease before they have become infected with SARS-CoV-2, they say.
“Identification of vulnerable individuals is a key priority in the current stage of the pandemic to guide protective measures and to design vaccination strategies,” concludes the team.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.