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After an outbreak of the SARS-CoV-2 Beta variant in the district of Schwaz/Austria, vaccination with Comirnaty vaccine (BNT162b2 mRNA, BioNTech-Pfizer) had been offered to all adult inhabitants (≥ 16 years) in March 2021. This made Schwaz one of the most vaccinated regions in Europe at that time (70% of the adult population took up the offer). In contrast, all other Austrian districts remained with low vaccine coverage.


We studied whether this rapid mass vaccination campaign provided indirect protection to unvaccinated individuals such as children (< 16 years) living in the same district.


To study the effect of the campaign we used two complementary approaches. We compared infection rates among the population of children (< 16 years) in Schwaz with (i) the child population from similar districts (using the synthetic control method), and (ii) with the child population from municipalities along the border of Schwaz not included in the campaign (using an event study approach).


Before the campaign, we observed very similar infection spread across the cohort of children in Schwaz and the control regions. After the campaign, we found a significant reduction of new cases among children of −64.5% (95%-CI: −82.0 to −30.2%) relative to adjacent border municipalities (using the event study model). Employing the synthetic control method, we observed a significant reduction of −42.8% in the same cohort.


Our results constitute novel evidence of an indirect protection effect from a group of vaccinated individuals to an unvaccinated group.


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  1. Goldman RD, Yan TD, Seiler M, Parra Cotanda C, Brown JC, Klein EJ, et al. Caregiver willingness to vaccinate their children against COVID-19: Cross sectional survey. Vaccine. 2020;38(48):7668-73.  https://doi.org/10.1016/j.vaccine.2020.09.084  PMID: 33071002 
  2. Skjefte M, Ngirbabul M, Akeju O, Escudero D, Hernandez-Diaz S, Wyszynski DF, et al. COVID-19 vaccine acceptance among pregnant women and mothers of young children: results of a survey in 16 countries. Eur J Epidemiol. 2021;36(2):197-211.  https://doi.org/10.1007/s10654-021-00728-6  PMID: 33649879 
  3. Bell S, Clarke R, Mounier-Jack S, Walker JL, Paterson P. Parents’ and guardians’ views on the acceptability of a future COVID-19 vaccine: A multi-methods study in England. Vaccine. 2020;38(49):7789-98.  https://doi.org/10.1016/j.vaccine.2020.10.027  PMID: 33109389 
  4. Montalti M, Rallo F, Guaraldi F, Bartoli L, Po G, Stillo M, et al. Would parents get their children vaccinated against SARS-CoV-2? rate and predictors of vaccine hesitancy according to a survey over 5000 families from Bologna, Italy. Vaccines (Basel). 2021;9(4):366.  https://doi.org/10.3390/vaccines9040366  PMID: 33920109 
  5. Kadkhoda K. Herd Immunity to COVID-19. Am J Clin Pathol. 2021;155(4):471-2.  https://doi.org/10.1093/ajcp/aqaa272  PMID: 33399182 
  6. Fontanet A, Cauchemez S. COVID-19 herd immunity: where are we? Nat Rev Immunol. 2020;20(10):583-4.  https://doi.org/10.1038/s41577-020-00451-5  PMID: 32908300 
  7. Harvey RA, Rassen JA, Kabelac CA, Turenne W, Leonard S, Klesh R, et al. Association of SARS-CoV-2 seropositive antibody test with risk of future infection. JAMA Intern Med. 2021;181(5):672-9.  https://doi.org/10.1001/jamainternmed.2021.0366  PMID: 33625463 
  8. Österreichische Agentur für Gesundheit und Ernährungssicherheit GmbH (AGES). Coronavirus. SARS-CoV-2-Varianten in Österreich. [Coronavirus. SARS-CoV-2 variants in Austria]. Wien: AGES. [Accessed: 8 Sep 2022]. German. Available from: https://www.ages.at/mensch/krankheit/krankheitserreger-von-a-bis-z/coronavirus#c12422
  9. Paetzold J, Kimpel J, Bates K, Hummer M, Krammer F, von Laer D, et al. Impacts of rapid mass vaccination against SARS-CoV2 in an early variant of concern hotspot. Nat Commun. 2022;13(1):612.  https://doi.org/10.1038/s41467-022-28233-8  PMID: 35105889 
  10. Milman O, Yelin I, Aharony N, Katz R, Herzel E, Ben-Tov A, et al. Community-level evidence for SARS-CoV-2 vaccine protection of unvaccinated individuals. Nat Med. 2021;27(8):1367-9.  https://doi.org/10.1038/s41591-021-01407-5  PMID: 34113015 
  11. Béraud G, Kazmercziak S, Beutels P, Levy-Bruhl D, Lenne X, Mielcarek N, et al. The French connection: the first large population-based contact survey in France relevant for the spread of infectious diseases. PLoS One. 2015;10(7):e0133203.  https://doi.org/10.1371/journal.pone.0133203  PMID: 26176549 
  12. Cunningham S. Causal inference. The Mixtape. New Haven & London: Yale University Press; 2021. ISBN 978-0-300-25168-5
  13. Kreif N, Grieve R, Hangartner D, Turner AJ, Nikolova S, Sutton M. Examination of the synthetic control method for evaluating health policies with multiple treated units. Health Econ. 2016;25(12):1514-28.  https://doi.org/10.1002/hec.3258  PMID: 26443693 
  14. Cho S-W. Quantifying the impact of nonpharmaceutical interventions during the COVID-19 outbreak: The case of Sweden. Econom J. 2020;23(3):323-44.  https://doi.org/10.1093/ectj/utaa025 
  15. Firpo S, Possebom V. Synthetic control method: inference, sensitivity analysis and confidence sets. J Causal Inference. 2018;6(2):20160026.  https://doi.org/10.1515/jci-2016-0026 
  16. Dobkin C, Finkelstein A, Kluender R, Notowidigdo MJ. The economic consequences of hospital admissions. Am Econ Rev. 2018;108(2):308-52.  https://doi.org/10.1257/aer.20161038  PMID: 30091560 
  17. Polack FP, Thomas SJ, Kitchin N, Absalon J, Gurtman A, Lockhart S, et al. Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine. N Engl J Med. 2020;383(27):2603-15.  https://doi.org/10.1056/NEJMoa2034577  PMID: 33301246 
  18. Madewell ZJ, Yang Y, Longini IM Jr, Halloran ME, Dean NE. Household secondary attack rates of SARS-CoV-2 by variant and vaccination status: an updated systematic review and meta-analysis. JAMA Netw Open. 2022;5(4):e229317.  https://doi.org/10.1001/jamanetworkopen.2022.9317  PMID: 35482308 
  19. Salo J, Hägg M, Kortelainen M, Leino T, Saxell T, Siikanen M, et al. The indirect effect of mRNA-based COVID-19 vaccination on healthcare workers’ unvaccinated household members. Nat Commun. 2022;13(1):1162.  https://doi.org/10.1038/s41467-022-28825-4  PMID: 35246536 
  20. Dorabawila V, Hoefer D, Bauer UE, Bassett MT, Lutterloh E, Rosenberg ES. Risk of Infection and Hospitalization Among Vaccinated and Unvaccinated Children and Adolescents in New York After the Emergence of the Omicron Variant. JAMA. 2022;327(22):2242-4.  https://doi.org/10.1001/jama.2022.7319 
  21. Andrews N, Stowe J, Kirsebom F, Toffa S, Rickeard T, Gallagher E, et al. Covid-19 vaccine effectiveness against the Omicron (B.1.1.529) Variant. N Engl J Med. 2022;386(16):1532-46.  https://doi.org/10.1056/NEJMoa2119451  PMID: 35249272 
  22. Hansen C, Schelde A, Moustsen-Helm I, Embor H-D, Eriksen R, Stegger M, et al. Vaccine effectiveness against infection and COVID-19-associated hospitalisation with the Omicron (B.1.1.529) variant after vaccination with the BNT162b2 or mRNA-1273 vaccine: A nationwide Danish cohort study. Research Square pre-print. 2022  https://doi.org/10.21203/rs.3.rs-1486018/v1 .

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