Why Does Homelessness Increase the Risk of COVID-19 Reinfection?
A new study suggests high levels of exposure to the virus can overcome even robust immune responses developed after the first infection.
boston homeless man at south station at risk of COVID-19 reinfection
Boston Globe, Getty Images

Homelessness is a significant predictor of COVID-19 reinfection, according to researchers from Boston Medical Center. Their new study, published in Clinical Infectious Diseases, found that housing insecurity was the only demographic factor associated with reinfection, suggesting that individuals who are experiencing homelessness are more at risk for reinfection than those with a stable living environment. In addition, pre-existing medical conditions and the severity of the disease after the first infection were not associated with a higher risk.

Analyzing Boston Medical Center (BMC) patients' medical records, researchers compared clinical and demographic characteristics—age, race/ethnicity, body mass index, homeless, and comorbidities, for example—of two groups: 75 individuals who tested positive for COVID-19 at least 90 days after an initial infection and 1,594 individuals who tested negative at least 90 days after an initial infection. The criteria matched the Centers for Disease Control and Prevention's requirements for diagnosing a reinfection: a repeat positive test separated by a minimum of 90 days, to differentiate between reinfection and prolonged shedding of the virus.

"Most individuals with a previous SARS-CoV-2 infection seem to be protected from the virus for many months or even longer, yet some individuals can become infected again with the virus only a few months later," explains Manish Sagar, MD, an infectious diseases physician at BMC, who oversaw the study.

The purpose of this study was to find out who exactly is at risk of this rapid reinfection—and why.

"We conducted this study to understand whether cases of reinfection with SARS-CoV-2 are associated with any demographic characteristics, or if reinfection is due to a deficiency in the patient's immune response," says Sagar.

To determine this, plasma from a subset of patients in each of the two groups was tested for the presence of antibodies that recognize SARS-CoV-2. To confirm reinfection, researchers sequenced the virus from a few patients after their first infection and compared it to the virus from the same patients after their second infection. None of the individuals in this study had received a COVID-19 vaccine because the data were collected prior to the vaccine rollout in Boston.

The 'why' and 'what now?' from the COVID-19 reinfection study

BMC researchers found that reinfection occurs even in the presence of antibodies acquired from a prior infection. No significant differences in antibody responses were found between the two groups—the patients testing positive after 90 days and the patients testing negative. Individuals who were reinfected still had antibodies present, suggesting that high levels of exposure to the virus may be able to overcome immune responses.

"The association of homelessness with COVID-19 reinfection may be a result of increased exposure to SARS-CoV-2, due to the difficulty of complying with COVID-19 health recommendations, like social distancing and mask usage." Click To Tweet

Sagar explains how this key finding may be related to people experiencing homelessness.

"The association of homelessness with COVID-19 reinfection may be a result of increased exposure to SARS-CoV-2, due to the difficulty of complying with COVID-19 health recommendations, like social distancing and mask usage," he says.

To prevent subsequent infections among people experiencing homelessness and housing insecurity, the researchers recommend policies aimed at reducing homelessness, along with increasing the rate of vaccination, which, they note, may not prevent reinfection but can protect against severe illness.

As a continuation of their work, researchers are currently exploring additional components of the immune system that may be important in the protection against SARS-CoV-2 re-infection. They are also focusing on transmission networks within the homeless population to understand if there are specific behaviors that are leading to higher rates of reinfection, which could help identify more specific potential mitigation strategies.


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