Adolescent COVID-19 Cases During the SARS-CoV-2 Delta and Omicron Variant Surges in Kentucky: Association With Vaccination and Prior Infection.

PURPOSE: Effectiveness of COVID-19 mRNA vaccines is influenced by SARS-CoV-2 variant and history of prior infection. Data regarding protection against SARS-CoV-2 infection among adolescents, accounting for prior infection and time since vaccination, are limited. METHODS: SARS-CoV-2 testing and immunization data from the Kentucky Electronic Disease Surveillance System and the Kentucky Immunization Registry, August-September 2021 (Delta predominance) and January 2022 (Omicron Predominance) among adolescents aged 12-17 years, were used to assess association of SARS-CoV-2 infection with mRNA vaccination and prior SARS-CoV-2 infection. Estimated protection was derived from prevalence ratios ([1-PR] × 100%). RESULTS: During Delta predominance, 89,736 tested adolescents were evaluated. Completion of primary series (second dose of mRNA vaccine ≥ 14 days prior to testing) and history of prior infection (> 90 days prior to testing) were both protective against SARS-CoV-2 infection (primary series: 81%, 95% confidence interval [CI] 79.7-82.3; prior infection: 66%, 95% CI 62.0-69.6). Prior infection plus primary series provided the greatest protection (92.3%, 95% CI 88.0-95.1). During Omicron predominance, 67,331 tested adolescents were evaluated. Primary series alone provided no benefit against SARS-CoV-2 infection after 90 days; prior infection was protective for up to one year (24.2%, 95% CI 17.2-30.7). Prior infection plus booster vaccination provided the greatest protection against infection (82.4%, 95% CI 62.1-91.8). DISCUSSION: Strength and duration of protection against infection provided by COVID-19 vaccination and prior SARS-CoV-2 infection differed by variant. Vaccination provided additional benefit to the protection offered by prior infection alone. Remaining up to date with vaccination is recommended for all adolescents regardless of infection history.

Association of Severe Acute Respiratory Syndrome Coronavirus 2 Vaccination or a Prior Positive Test Result in Adolescents during the Delta Variant Surge in Kentucky.

In a cross-sectional study of 89 736 adolescents in Kentucky, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination provided an estimated protection against infection of 81% when the highly transmissible Delta variant was predominant. Vaccination provided added benefit to those with a history of prior infection. These findings support the recommendation that all adolescents receive SARS-CoV-2 vaccination.

Protective Immunity after Natural Infection with Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) - Kentucky, USA, 2020.

BACKGROUND: As vaccine supply and access remain limited in many parts of the world, understanding the duration of protection from reinfection after natural infection is important. METHODS: Distinct individuals testing positive and negative for SARS-CoV-2 between March 6, 2020, and August 31, 2020, in Kentucky, USA, were identified using the Kentucky National Electronic Disease Surveillance System. Individuals were followed for occurrence of a positive test for SARS-CoV-2 from 91 days after their initial test result through December 31, 2020. Protection from reinfection provided by a prior infection was calculated and additional analyses evaluated impact of age, sex, symptom status, long-term care facility connection, testing occurrence and frequency, and time from initial infection. RESULTS: The protective effect from prior infection was 80.3% (95% CI, 78.2%-82.2%) for those aged 20-59 years and 67.4% (95% CI, 62.8%-71.4%) for those aged ≥60 years. At 30-day time periods through 270 days (with limited exceptions), protection was estimated to be >75% for those aged 20-59 years and >65% for those aged ≥60 years. Factors associated with repeat positive testing included a connection to a long-term care facility, duration of potential exposure, and absence of symptoms during initial infection. CONCLUSIONS: Natural infection provides substantial and persistent immunologic protection for a period of several months for most individuals, although subpopulations may be at greater risk of repeat positive testing and potential poor outcomes associated with reinfection. These subgroups include individuals aged ≥60 years, residents and staff of long-term care facilities, and those who have mild or asymptomatic illness with initial infection. Continued emphasis on vaccination and infection prevention and control strategies remains critically important in reducing the risk of reinfection and associated severe outcomes for these groups.

Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination - Kentucky, May-June 2021.

Although laboratory evidence suggests that antibody responses following COVID-19 vaccination provide better neutralization of some circulating variants than does natural infection (1,2), few real-world epidemiologic studies exist to support the benefit of vaccination for previously infected persons. This report details the findings of a case-control evaluation of the association between vaccination and SARS-CoV-2 reinfection in Kentucky during May-June 2021 among persons previously infected with SARS-CoV-2 in 2020. Kentucky residents who were not vaccinated had 2.34 times the odds of reinfection compared with those who were fully vaccinated (odds ratio [OR] = 2.34; 95% confidence interval [CI] = 1.58-3.47). These findings suggest that among persons with previous SARS-CoV-2 infection, full vaccination provides additional protection against reinfection. To reduce their risk of infection, all eligible persons should be offered vaccination, even if they have been previously infected with SARS-CoV-2.