A new study that used health data from 212,984 Americans who experienced COVID-19 reinfections found that severe SARS-CoV-2 infections tended to foreshadow similar severity of subsequent infections. The researchers also found that long COVID was more likely to occur after a first infection compared to a reinfection.
The findings were published today in Communications Medicine.
"More than three years after the start of the COVID-19 pandemic, individuals are frequently reporting multiple COVID-19 infections. However, these reinfections remain poorly understood," the authors write.
About 7% report reinfections
The study was part of the National Institutes of Health's Researching COVID to Enhance Recovery (RECOVER) initiative, and used the electronic health records of 3.1 million Americans. The researchers looked at records from more than 200,000 who reported original infections from March 1, 2020 through Dec. 31, 2022, and experienced a second infection by March 2023.
Overall, 6.9% of people in the study had a documented reinfection, which is likely an underestimate in the wake of home testing, the authors said.
Most people in the study had COVID twice, but 478 reported three or more infections. The authors included reinfections only if they occurred 60 or more days after an earlier COVID-19 infection.
Fewer reinfected patients (14.3%) had a documented vaccination prior to their COVID index date than patients who did not have reinfection (25.0%), the authors said, and those with reinfections were almost 5 years younger than those without reinfection.
The authors note, "Women make up nearly two-thirds of the study cohort and a larger proportion of those with a documented reinfection."
Women make up nearly two-thirds of the study cohort and a larger proportion of those with a documented reinfection.
The Omicron variant period saw the most reinfections, with reinfection spikes documented near winter holidays and in the early summer.
"The large number of reinfections during Omicron BA.1 and BA.2 makes it challenging to draw conclusions about comparing reinfections between variants because there may be other factors, such as adherence to masking or social distance policies, that impacted the likelihood of exposure and subsequent reinfections," the authors said.
Severity linked in infections
The authors found that the vast majority of people (87.5%) had a mild initial infection without an emergency department (ED) visit. Of those with a mild initial infection without an ED visit, a similar rate of first reinfections, 87.4%, were also mild.
One third of those with an initial infection requiring an ED visit also required an ED visit for a reinfection. And 27% of those with severe cases, defined as being hospitalized for their initial infections, also received hospital care for a reinfection.
In fact, only 45.3% of first reinfections among those who experienced a severe initial infection were mild; 8.3% were severe, and 6.1% occurred within 60 days of death.
Long-COVID diagnoses were most common among those with a first reinfection in the Delta period, but the authors warned that diagnostic coding and clinician understanding of long COVID shifted significantly during the study period.
Finally, in looking at biomarkers, the authors noted that reinfected people had lower levels of albumin, a liver protein. Low albumin could be a possible risk factor for reinfection with COVID, and albumin has also been shown to be a biomarker for long COVID, the authors said, and needs further investigation.
