{'fraction_non_alphanumeric': 0.05214582371942778, 'fraction_numerical': 0.05629903091832026, 'mean_word_length': 5.194285714285714, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Protection against symptomatic disease with the delta and omicron BA.1/BA.2 variants of SARS-CoV-2 after infection and vaccination in adolescents: national observational test-negative case control study, August 2021 to March 2022, England

Background Little is known about the protection following prior infection with different SARS-CoV-2 variants, COVID-19 vaccination, and a combination of the two (hybrid immunity) in adolescents. Methods We used national SARS-CoV-2 testing and COVID-19 mRNA vaccination data in England to estimate protection following previous infection and vaccination against symptomatic PCR-confirmed delta and omicron (BA.1 or BA.2) variants in 11-17-year-olds using a test-negative case-control design. Findings By 31 March 2022, 63.6% of 16-17-year-olds and 48.2% of 12-15-year-olds had received more than one COVID-19 mRNA vaccine dose. Between 08 August 2021 and 31 March 2022, 1,161,704 SARS-CoV-2 PCR-tests were successfully linked to COVID-19 vaccination status. In unvaccinated adolescents, prior infection with wildtype, alpha or delta provided greater protection against subsequent delta infection than subsequent omicron; prior omicron infection provided had the highest protection against omicron reinfection (59.3%; 95%CI: 46.7-69.0). In infection-naive adolescents, vaccination provided lower protection against symptomatic omicron infection than delta, peaking at 64.5% (95%CI; 63.6-65.4) 2-14 days after dose two and 62.9% (95%CI; 60.5-65.1) 2-14 weeks after dose three, with rapidly waning protection after each dose. Previously infected and vaccinated adolescents had the highest protection, irrespective of primary infecting SARS-CoV-2 strain. The highest protection against omicron was observed in vaccinated adolescents with prior omicron infection, reaching 96.4% (95%CI, 84.4-99.1) at 15-24 weeks post dose two. Interpretation All variants provide some protection against symptomatic reinfection and vaccination adds to protection. Vaccination provides low-to-moderate protection against symptomatic omicron infection, with waning protection after each dose, while hybrid immunity provides the most robust protection.