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

Abstract

Although reinfections with SARS-CoV-2 have occurred in the United States with increasing frequency, U.S. epidemiologic trends in reinfections and associated severe outcomes have not been characterized. Weekly counts of SARS-CoV-2 reinfections, total infections, and associated hospitalizations and deaths reported by 18 U.S. jurisdictions during September 5, 2021-December 31, 2022, were analyzed overall, by age group, and by five periods of SARS-CoV-2 variant predominance (Delta and Omicron [BA.1, BA.2, BA.4/BA.5, and BQ.1/BQ.1.1]). Among reported reinfections, weekly trends in the median intervals between infections and frequencies of predominant variants during previous infections were calculated. 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. The median interval between infections ranged from 269 to 411 days by week, 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. To prevent severe COVID-19 outcomes, including those following reinfection, CDC recommends staying up to date with COVID-19 vaccination and receiving timely antiviral treatments, when eligible.

FIGURE 1

Percentages of SARS-CoV-2 reinfections among all infections for COVID-19 cases (A) and COVID-19–associated hospitalizations (B), by week of positive specimen collection date, age group, and SARS-CoV-2 variant period — 18 U.S. jurisdictions, September 5, 2021–December 31, 2022 * A SARS-CoV-2 reinfection was defined as a SARS-CoV-2 RNA or antigen detection (based on confirmatory or presumptive laboratory evidence, as defined by the Council of State and Territorial Epidemiologists) in a respiratory specimen collected >90 days after a previous confirmed or probable COVID-19 case in the same person. https://ndc.services.cdc.gov/case-definitions/coronavirus-disease-2019-2021/ ^† Periods were defined using ≥50% SARS-CoV-2 variant proportions from national genomic surveillance: ancestral strain (April 3, 2021, and earlier); Alpha (April 4–June 19, 2021); Delta (June 20–December 18, 2021); BA.1 comprising Omicron B.1.1.529 and BA.1.1 (December 19, 2021–March 19, 2022); BA.2 comprising BA.2 and BA.2.12.1 (March 20–June 18, 2022); and BA.4/BA.5 comprising BA.4, BA.4.6, and BA.5 (June 19–November 5, 2022). The BQ.1/BQ.1.1 period (November 6–December 31, 2022) also included other lineages with similar spike protein substitutions and was defined based on when BA.4/BA.4.6/BA.5 lineages reached <50%, as these other lineages increased. https://covid.cdc.gov/covid-data-tracker/#variant-proportions ^§ Data on reinfection–associated COVID-19 cases were included from 18 jurisdictions, representing 45% of the U.S. population: California, Colorado, District of Columbia, Georgia, Indiana, Kentucky, Louisiana, Massachusetts, Minnesota, Nebraska, New Jersey, New York, New York City, North Carolina, Oregon, Philadelphia, Tennessee, and Washington. Data on COVID-19 reinfection-associated hospitalizations were included from 10 jurisdictions: California, Colorado, Georgia, Minnesota, New Jersey, New York City, Oregon, Philadelphia, Tennessee, and Washington.

FIGURE 2

Weekly proportions of SARS-CoV-2 reinfections, by variant period of the previous infection and median time to reinfection — 17 U.S. jurisdictions, September 5, 2021–December 31, 2022 * A SARS-CoV-2 reinfection was defined as SARS-CoV-2 RNA or antigen detection (based on confirmatory or presumptive laboratory evidence, as defined by the Council of State and Territorial Epidemiologists) on a respiratory specimen collected >90 days after a previous confirmed or probable COVID-19 case in the same person. https://ndc.services.cdc.gov/case-definitions/coronavirus-disease-2019-2021/ ^† Periods of previous infections and reinfections were defined using ≥50% SARS-CoV-2 variant proportions from national genomic surveillance: ancestral strain (April 3, 2021, and earlier); Alpha (April 4–June 19, 2021); Delta (June 20–December 18, 2021); BA.1 comprising Omicron B.1.1.529 and BA.1.1 (December 19, 2021–March 19, 2022); BA.2 comprising BA.2 and BA.2.12.1 (March 20–June 18, 2022); and BA.4/BA.5 comprising BA.4, BA.4.6, and BA.5 (June 19–November 5, 2022). The BQ.1/BQ.1.1 period (November 6–December 31, 2022) also included other lineages with similar spike protein substitutions and was defined based on when BA.4/BA.4.6/BA.5 lineages reached <50%, as these other lineages increased. https://covid.cdc.gov/covid-data-tracker/#variant-proportions ^§ Overall weekly trends in the median time to reinfection (i.e., median days between positive specimen collection dates) were estimated by weighting the reported medians using the number of weekly reinfections per jurisdiction. ^¶ Data were included for 17 jurisdictions: California, Colorado, District of Columbia, Georgia, Indiana, Kentucky, Louisiana, Massachusetts, Minnesota, Nebraska, New Jersey, New York, New York City, North Carolina, Oregon, Philadelphia, and Washington.