Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2022 Nov 28;40(50):7195-7200.
doi: 10.1016/j.vaccine.2022.09.042. Epub 2022 Sep 19.

Protection of vaccination versus hybrid immunity against infection with COVID-19 Omicron variants among Health-Care Workers

Fotinie Ntziora  1 , Evangelia Georgia Kostaki  2 , Amalia Karapanou  3 , Maria Mylona  3 , Ioulia Tseti  4 , Nikolaos V Sipsas  5 , Dimitrios Paraskevis  6 , Petros P Sfikakis  7
Affiliations

Protection of vaccination versus hybrid immunity against infection with COVID-19 Omicron variants among Health-Care Workers

Fotinie Ntziora et al. Vaccine. .

Abstract

Background aim: The Omicron COVID-19 variants BA.1* and BA.2* evade immune system leading to increased transmissibility and breakthrough infections. We aim to test the hypothesis that immunity achieved post COVID-19 infection combined with vaccination (hybrid immunity), is more effective against Omicron infection than vaccination alone in a health-care setting.

Methods: Data on regular pre-emptive PCR testing from all Health-Care Workers (HCWs) at Laiko University Hospital from 29th December 2020, date on which the national COVID-19 immunization program began in Greece, until 24th May 2022, were retrospectively collected and recorded. The infection rate was calculated after December 21st, 2021, when Omicron was the predominant circulating variant in Greece, as the total number of infections (positive PCR COVID-19 test regardless of symptoms) divided by the total person-months at risk.

Results: Of 1,305 vaccinated HCWs who were included in the analysis [median age of 47 (IQR: 36, 56) years, 66.7 % women], 13 % and 87 % had received 2 or 3 vaccine doses (full and booster vaccination), respectively. A COVID-19 infection had occurred in 135 of 1,305 of participants prior to Omicron predominance. Of those 135 HCWs with hybrid immunity only 13 (9.6 %) were re-infected. Of the 154 and 1,016 HCWs with full and booster vaccination-induced immunity, respectively, 71 (46.1 %, infection rate 13.4/100 person-months) and 448 (44.1 %, infection rate 12.2/100 person-months) were infected during the follow up period. No association between gender or age and COVID-19 infection was found and none of the participants had a severe infection or died.

Conclusions: Hybrid immunity confers higher protection by almost 5-fold compared to full or booster vaccination for COVID-19 infection with the Omicron variant among HCWs who are at high risk of exposure. This may inform public health policies on how to achieve optimal immunity in terms of the timing and mode of vaccination.

Keywords: COVID-19; Health-Care Workers (HCWs); Hybrid immunity; Infection rate; Vaccine.

PubMed Disclaimer

Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Comparison of COVID-19 proportion of Omicron infections between fully and booster vaccinated Health-Care Workers with or without hybrid immunity (by a previous COVID-19 infection) during the follow up period.
Fig. 2
Fig. 2
Omicron infection rate per 100 person-months for fully and booster vaccinated Health-Care Workers with or without hybrid immunity (by a previous COVID-19 infection) during the follow up period.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Altarawneh H.N., Chemaitelly H., Hasan M.R., Ayoub H.H., Qassim S., AlMukdad S., et al. Protection against the Omicron Variant from Previous SARS-CoV-2 Infection. N Engl J Med. 2022;386(13):1288–1290. - PMC - PubMed
    1. Ntziora F, Kostaki EG, Grigoropoulos I, Karapanou A, Kliani I, Mylona M, et al. Vaccination hesitancy among Health-Care-Workers in Academic Hospitals is associated with a 12-fold increase in the risk of COVID-19 infection: a nine-month Greek cohort study. Viruses 2021 Dec 24;14(1):26. Doi:10.3390/v14010026. PMID: 35062230; PMCID: PMC8779273. - PMC - PubMed
    1. World Health Organization (WHO), Tracking SARS-CoV-2 variants, https://www.who.int/activities/tracking-SARS-CoV-2-variants (accessed 8/7/2022).
    1. Chemaitelly H., Bertollini R., Abu-Raddad L.J. National Study Group for COVID-19 Epidemiology. Efficacy of natural immunity against SARS-CoV-2 reinfection with the beta variant. N Engl J Med. 2021;385(27):2585–2586. - PMC - PubMed
    1. Abu-Raddad LJ, Chemaitelly H, Ayoub HH, Coyle P, Malek JA, Ahmed AA, et al. Introduction and expansion of the SARS-CoV-2 B.1.1.7 variant and reinfections in Qatar: A nationally representative cohort study. PLoS Med. 2021 Dec 16;18(12):e1003879. doi: 10.1371/journal.pmed.1003879. PMID: 34914711; PMCID: PMC8726501. - PMC - PubMed

Publication types

Supplementary concepts