A man was infected with COVID-19 twice and developed more severe symptoms the second time around, according to a new case study published in the medical journal The Lancet.
The man first tested positive for coronavirus on April 18, 2020, and then again on June 5, 2020, with genetic analysis of the virus showing significant differences between the "variant" associated with the infection, scientists in Nevada said.
The 25-year-old from the US first presented virus symptoms of sore throat, cough, headache, nausea, and diarrhoea in late March but recovered by the end of April.
He felt better until the end of May and even tested negative twice for the virus that month.
But in late May, he went to an urgent care centre with similar virus symptoms and five days later, he experienced low oxygen levels and shortness of breath.
He was treated at the accident and emergency department where a chest x-ray showed that he had developed pneumonia.
"The patient required ongoing oxygen support in hospital and reported symptoms that included myalgia [muscle pain], cough, and shortness of breath," the researchers said.
This is the first individual in North America who appears to have been reinfected with the virus and he joins a mere handful of cases globally.
Individuals who have been reinfected with the virus had previously emerged in Belgium, Hong Kong and the Netherlands.
The 89-year-old woman in the Netherlands died due to complications from her second infection. She had undergone chemotherapy beforehand.
Scientists said her case was likely to be a reinfection rather than the first one continuing to replicate in her body.
The woman, who had a weakened immune system, also had a more severe infection the second time around.
A person in Ecuador, also appeared to have developed more severe symptoms the second time around, scientists wrote in The Lancet.
It remains unknown how long people who have contracted COVID-19 are immune although many experts have said that they are likely immune for a certain period of time.
An encouraging study in Iceland showed that antibodies that help humans fight off the virus likely last for at least four months and do not fade quickly.
This is encouraging for vaccine efforts which will attempt to trigger that immune response in humans to protect them from the virus.
But scientists in the Netherlands point out that reinfection in seasonal coronaviruses have occurred as early as six months after reinfection.