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

Fotinie Ntziora; Evangelia Georgia Kostaki; Amalia Karapanou; Maria Mylona; Ioulia Tseti; Nikolaos V Sipsas; Dimitrios Paraskevis; Petros P Sfikakis

doi:10.1016/j.vaccine.2022.09.042

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

Vaccine. 2022 Nov 28;40(50):7195-7200. doi: 10.1016/j.vaccine.2022.09.042. Epub 2022 Sep 19.

Authors

Fotinie Ntziora¹, Evangelia Georgia Kostaki², Amalia Karapanou³, Maria Mylona³, Ioulia Tseti⁴, Nikolaos V Sipsas⁵, Dimitrios Paraskevis⁶, Petros P Sfikakis⁷

Affiliations

¹ 1st Department of Propaedeutic Internal Medicine, Laiko Hospital, Medical School, National and Kapodistrian University of Athens, 11527 Athens, Greece. Electronic address: fntziora@med.uoa.gr.
² Department of Hygiene, Epidemiology and Medical Statistics, Medical School, National and Kapodistrian University of Athens, 11527 Athens, Greece. Electronic address: ekostakh@med.uoa.gr.
³ 1st Department of Propaedeutic Internal Medicine, Laiko Hospital, Medical School, National and Kapodistrian University of Athens, 11527 Athens, Greece.
⁴ Uni-Pharma S.A., 14564 Kifissia, Greece. Electronic address: jtsetis@uni-pharma.gr.
⁵ Pathophysiology Department, Laiko Hospital, Medical School, National and Kapodistrian University of Athens, 11527 Athens, Greece. Electronic address: nsipsas@med.uoa.gr.
⁶ Department of Hygiene, Epidemiology and Medical Statistics, Medical School, National and Kapodistrian University of Athens, 11527 Athens, Greece; National Public Health Organization, 15123, Athens, Greece. Electronic address: dparask@med.uoa.gr.
⁷ 1st Department of Propaedeutic Internal Medicine, Laiko Hospital, Medical School, National and Kapodistrian University of Athens, 11527 Athens, Greece. Electronic address: psfikakis@med.uoa.gr.

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.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

COVID-19* / prevention & control
Female
Humans
Male
Retrospective Studies
SARS-CoV-2
Vaccination

Supplementary concepts

SARS-CoV-2 variants