Q&A: SARS-CoV-2 reinfection rate ‘likely higher’ than previously thought

A 43-year-old man in the United States tested positive for SARS-CoV-2 twice within 4 months, according to a paper in BMJ Case Reports.

Researchers said the case highlights the possibility of reinfection with SARS-CoV-2 and provides an opportunity to expand the “limited data” that are available regarding SARS-CoV-2 reinfection.

“We felt it important to document this case report of presumed COVID‐19 reinfection to further elucidate the natural history of COVID‐19 reinfection,” Jessica Tuan, MD, MS, an infectious diseases fellow in the department of internal medicine at the Yale University School of Medicine and coauthor of the paper, told Healio Primary Care.

Concerns about reinfection are increasing with the emergence of new variants, according to senior coauthor Onyema Ogbuagu, MBBCh, FACP, FIDSA, an infectious disease specialist and director of HIV Clinical Trials in the Yale AIDS Program. He warned that individuals previously infected with earlier strains of SARS-CoV-2 “would be immediately vulnerable to reinfection with emerging variants like the South Africa strain.”

Below, Tuan discusses the incidence of SARS-CoV-2 reinfection, waning immunity, the severity of disease in reinfection and more.

Q: How many known cases are there of reinfection with SARS‐CoV‐2?

A: As of September 2020, there were six documented cases of COVID‐19 reinfection globally, according to the European Centre for Disease Prevention and Control. To date, the number of confirmed cases has increased to 47, although the number of suspected cases is much higher.

The current number of definitive reinfection cases of COVID‐19 is unclear given lack of capacity for sequencing and underreporting that is readily available for identification of reinfection cases. With these capacity issues, combined with increasing circulating SARS‐CoV‐2 variants, the number of COVID‐19 reinfection cases is likely higher than what was once previously thought.

Q: What evidence is there to suggest that these cases are reinfections and not persistent viral shedding?

A: A definitive diagnosis of COVID‐19 reinfection would be confirmed via separate SARS‐CoV‐2 strains identified at separate COVID‐19 episodes. However, multiple interval negative COVID‐19 tests and a relatively high SARS-CoV‐2 viral load (or low cycle threshold) on a second presentation would also be highly suggestive of COVID‐19 reinfection. If the SARS‐CoV‐2 virus can be cultured in a second episode, this also would likely also suggest reinfection, rather than nonviable, noninfectious virus.

Q: How are people becoming reinfected?

A: People are becoming reinfected likely due to waning immunity, which heightens the risk of COVID‐19 reinfection as well as underlying host factors such as immunosuppression history. These factors, in combination with increased quantities of circulating SARS‐CoV‐2 variants make individuals more susceptible to COVID‐19 reinfection. When it comes to mutations in this virus, the principle of survival of the fittest mutation applies.

Q: What is the average length of time between initial infection and reinfection?

A: Prior studies have documented anywhere from 10 to 185 days between time of the initial COVID‐19 episode to an episode of COVID‐19 reinfection. Recent data of documented COVID‐19 reinfection cases suggests that the average interval between episodes is approximately 85 days.

Q: Is disease severity better or worse the second time around? Why?

A: The disease severity may vary in an episode of COVID‐19 reinfection. In the case of our patient, the initial episode of COVID‐19 was severe, followed by a milder case of COVID‐19. The variable presentation of disease severity upon reinfection likely has to do with durability of immunity, SARS‐CoV‐2 strain upon reinfection and host factors including underlying immunosuppression history.

Reference:

Tuan J, et al. BMJ Case Rep. 2021;doi:10.1136/bcr-2020-240531.