First case of COVID-19 reinfection confirmed in the U.S.: study

TORONTO -- U.S. researchers have confirmed the country's first case of COVID-19 reinfection, indicating that exposure to the virus may not translate to total immunity.

The first study to confirm a case of coronavirus reinfection in the U.S. found evidence that an individual with no known immune disorders or underlying health conditions was infected with SARS-CoV-2, the virus that causes COVID-19, in two separate instances.

According to a new case study, published Monday in The Lancet, the 25-year-old Nevada man was infected by two different SARS-CoV-2 variants within a 48-day timeframe, while testing negative between each infection.

Researchers reported that the patient’s second infection was more severe, resulting in hospitalization with oxygen support.

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Dr. Mark Pandori, director of the Nevada State Public Health Laboratory, said the findings indicate that previous exposure to COVID-19 does not mean an individual is guaranteed total immunity from the disease. However, he says more research is needed.

"There are still many unknowns about SARS-CoV-2 infections and the immune system's response, but our findings signal that a previous SARS-CoV-2 infection may not necessarily protect against future infection," Pandori said in the study.

The patient was first diagnosed with COVID-19 in April, according to the study. He got better around April 27, and tested negative for the virus twice afterwards.

In June after experiencing severe COVID-19 symptoms including fever, headache, dizziness, cough, nausea and diarrhea, the patient was hospitalized and tested positive for the virus a second time.

The genomes of the patient’s virus samples were sequenced in April and June, displaying "significant genetic differences" between the two cases. Researchers say this implies that the patient was infected twice by two distinct SARS-CoV-2 infections.

The study says the patient has since been discharged from the hospital and has recovered from the second infection.

Pandori noted that all individuals, whether previously diagnosed with the novel coronavirus or not, should continue to take the necessary safety precautions to prevent infection such as physical distancing, wearing a face mask and handwashing.

"It is important to note this is a singular finding and does not provide generalizability of this phenomenon. While more research is needed, the possibility of reinfections could have significant implications for our understanding of COVID-19 immunity, especially in the absence of an effective vaccine," Pandori said.

The new case marks the fifth confirmation of COVID-19 reinfection globally.

In August, Hong Kong researchers said they found the first documented case of coronavirus reinfection in a 33-year-old man after he tested positive for the disease twice in the past year.

At least three other reinfection cases have since been confirmed in Belgium, the Netherlands and Ecuador. However, researchers noted that only the Ecuador reinfection case displayed worse disease outcomes than the first infection.

The cases from Belgium and the Netherlands did not show any difference in the severity of symptoms. In the Hong Kong case, researchers said the man experienced symptoms during his first bout of COVID-19, but didn't have any obvious symptoms the second time.

"We need more research to understand how long immunity may last for people exposed to SARS-CoV-2 and why some of these second infections, while rare, are presenting as more severe," Pandori said. "So far, we’ve only seen a handful of reinfection cases, but that doesn’t mean there aren’t more, especially as many cases of COVID-19 are asymptomatic."

POSSIBLE CAUSES OF COVID-19 REINFECTION

Researchers present several hypotheses in the study to potentially explain the severity of the second infection, including the possibility that the patient encountered a very high dose of the virus, causing a more acute reaction the second time.

The study reported that the patient may have also come in contact with a "more virulent version of the virus." Another hypothesis is that the presence of antibodies made the subsequent infection worse. The study says this phenomenon, known as antibody-dependent enhancement, has previously been seen with the SARS-CoV betacoronavirus as well as other diseases, including dengue fever.

The authors explained there is a "very slim possibility" of a continuous infection involving some form of deactivation and reactivation of antibodies, but noted that proving this hypothesis would require a mutational rate of SARS-CoV-2 that has not currently been observed.

According to the study, another explanation could be a simultaneous co-infection of both strains of the virus. However, researchers said this would mean that the second strain would have gone undetected in April and conversely, the first strain would need to be depleted before the June infection.

This possibility does not account for the genotype switch in this patient, the study said.

However, the authors acknowledged there were some limitations to their study. Researchers say they were unable to undertake any evaluation of the immune response to the first episode of SARS-CoV-2 infection and were not able to fully assess the efficacy of the immune responses, such as neutralizing antibody titers, during the second infection.

They also noted that this case and other confirmed reinfection cases occurred among patients who displayed COVID-19 symptoms. The study noted that there is a possibility that many infections and reinfections among individuals may be asymptomatic and are likely to remain undetected under current global testing practices.

"Overall, there is a lack of comprehensive genomic sequencing of positive COVID-19 cases both in the U.S. and worldwide, as well as a lack of screening and testing, which limits the ability of researchers and public health officials to diagnose, monitor, and obtain genetic tracking for the virus," Pandori said.