A new study (Trends in Laboratory-Confirmed SARS-CoV-2 Reinfections and Associated Hospitalizations and Deaths Among Adults Aged ≥18 Years — 18 U.S. Jurisdictions, September 2021–December 2022 | MMWR (cdc.gov)) examines the epidemiological trends of SARS-CoV-2 reinfections and the association with severe outcomes.
The investigators report that during the time period of September 2021 (Delta) to December 2022 (Omicron), the percentages of reinfections among cases, hospitalizations and deaths all increased significantly as reported by 18 jurisdictions in the U.S. Increases were most pronounced among young adults ages 18 – 49 years compared with older adults. On average, 12.7% of all infections during this time period were reinfections. The increase in reinfections is likely related to the increasing transmissibility and immune evasion of Omicron variants.
As a percentage of all infections, reinfections increased substantially from the Delta (2.7%) to the Omicron BQ.1/BQ.1.1 (28.8%) periods. During the same periods, increases in the percentages of reinfections among COVID-19–associated hospitalizations (from 1.9% [Delta] to 17.0% [Omicron BQ.1/BQ.1.1]) and deaths (from 1.2% [Delta] to 12.3% [Omicron BQ.1/BQ.1.1]) were also substantial.
Percentages of all COVID-19 cases, hospitalizations, and deaths that were reinfections were consistently higher across variant periods among adults aged 18–49 years compared with those among adults aged ≥50 years.
Among persons reinfected in September 2021, 90.5% had been previously infected during the period when the ancestral strain was predominant (2020), and 9.5% had been previously infected during the Alpha variant period (early 2021).
The median interval between infections ranged from 269 to 411 days, with a steep decline at the start of the BA.4/BA.5 period, when >50% of reinfections occurred among persons previously infected during the Alpha variant period or later.
Higher percentages of reinfections among COVID-19 cases and associated hospitalizations and deaths were observed among younger adults compared with older adults, particularly in late 2022. The higher percentages in younger age groups might be attributable to multiple factors, including higher cumulative incidence of first infections, later eligibility for vaccination, lower vaccination coverage, increased exposure risk, and a possible survival bias because of less severe initial infections.
I fear that many people that have been previously infected are under the impression that they will have durable immunity resulting from the infection. There is mounting evidence and every reason to believe that infection-based immunity wanes similar to vaccination-induced immunity. I also fear that people previously infected are under the impression that subsequent reinfections will necessarily be milder and therefore not consider obtaining early treatment with antivirals for those with above average risk.
Further, it has become clear that the risk for Long COVID or PASC (post-acute sequelae of COVID-19 infection) increases with each reinfection.
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