Waning immunity after severe first Covid-19 infection may turn patients more vulnerable for reinfection

Severe infection first time around may be followed by milder symptoms second time, study said

Waning immunity in some people following the first episode of infection with the novel coronavirus may make them more susceptible to reinfection, say doctors in a new case report.

While a decline in the levels of antibodies against the SARS-CoV-2 virus after first encounter with the virus may heighten reinfection risk, the research, published in the journal BMJ Case Reports, noted that severe infection first time around may be followed by milder symptoms second time.

The authors from Yale University School of Medicine in the US described the case of a man in his 40s who was admitted to hospital with mild COVID-19 infection four months after an initial bout of severe disease in April 2020.

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They said the man had well-controlled type 2 diabetes, an underactive thyroid gland, and was obese -- known risk factors for severe COVID-19 infection.

During his first bout of infection he was hospitalised with breathing difficulties and a high-pitched wheeze caused by disrupted airflow.

According to the authors, the man also developed respiratory failure, and required mechanical ventilation and blood thinners as well as various other drugs used to treat COVID-19.

When he stabilized, they said he was discharged to an acute care facility for rehabilitation.

Then in August 2020, the report said he tested positive for the coronavirus again after four interval negative tests during the preceding three months.

While he stayed at the hospital for only one day this time, two weeks later he was admitted again with shortness of breath, intermittent episodes of choking, and shortness of breath.

Explaining the positive test results several months apart, the authors suggested this might be attributable to reinfection with the virus.

They believe the milder symptoms second time around could be because of residual immunity from the first severe infection.

"The role of the presence or absence of antibodies after initial infection in survivors of a first episode of COVID-19 and its role in mitigating the risk of SARS-CoV-2 reinfection is not clearly defined," the authors noted in the report.

They believe it is plausible that waning immunity or absence of antibodies after the first episode of SARS-CoV-2 infection may make one more susceptible to reinfection.

"Future observations would certainly shed more light on this if this hypothesis holds true," the authors noted.