Through the use of sequencing data, researchers in Hong Kong presented a case study providing the strongest evidence yet that individuals can become reinfected with SARS-CoV-2 after clearing a first infection.
There have been previous reports of reinfection with SARS-CoV-2. But in the absence of genome sequencing, it has been unclear whether second cases are truly reinfections, or flare-ups of an infection that had been only temporarily subdued.
In the case now reported by HKU, the genome sequencing data leaves little doubt that the individual, an immunocompetent 33-year-old technology worker from Hong Kong, was infected on two separate occasions. The person’s second infection was detected at an airport screening when he returned from business travel in Spain, and sequencing showed that he was infected with two distinct strains that differed from each other in 24 nucleotides.
The individual had previously been diagnosed with COVID-19 142 days earlier. His first infection was clinically mild, and the second infection remained asymptomatic.
The paper reporting the case has been accepted for publication in Clinical Infectious Diseases, but is not available as a preprint yet, leaving many details of the case unclear. Critically, it is not clear at this point whether the individual developed a neutralizing antibody response after his first infection.
It is also unknown whether the individual was infectious during their second episode.
WHO’s COVID-19 technical lead Maria van Kerkhove addressed the case at the World Health Organization’s weekly COVID-19 press conference on Aug. 24.
Van Kerkhove pointed out that “there’s been more than 24 million [COVID-19] cases reported to date, and we need to look at something like this on a population level.”
Documenting cases of reinfection is “very important,” she said. But “we need to not jump to any conclusions.”
The overall picture eight months into the pandemic, while necessarily still incomplete, is one of a typically strong immune response that occurs in asymptomatic, mild and severe clinical cases.
Both longitudinal studies, which follow the same individuals over time, and cross-sectional studies, which look at populations over time, are being conducted to see whether that immune response is long-lasting.
Kerkhove said that on balance, the emerging evidence suggests that immunity is lasting, although given that the pandemic itself is only eight months old, “lasting” immunity is still a relative term.
Cross-sectional studies, she said, “show there may be a slight decline or waning” of immunity. But “from the longitudinal studies that are underway... We do see a strong antibody response… that stays at that same level.”