Timing of last COVID-19 vaccine dose and SARS-CoV-2 breakthrough infections in fully (boosted) vaccinated healthcare personnel

H C Maltezou; M N Gamaletsou; T V Giannouchos; D-M Koukou; A Karapanou; F Sourri; N Syrimi; N Lemonakis; E Peskelidou; K Papanastasiou; K Souliotis; A Lourida; P Panagopoulos; D Hatzigeorgiou; N V Sipsas

doi:10.1016/j.jhin.2022.11.016

Timing of last COVID-19 vaccine dose and SARS-CoV-2 breakthrough infections in fully (boosted) vaccinated healthcare personnel

J Hosp Infect. 2023 Feb:132:46-51. doi: 10.1016/j.jhin.2022.11.016. Epub 2022 Dec 5.

Authors

H C Maltezou¹, M N Gamaletsou², T V Giannouchos³, D-M Koukou⁴, A Karapanou⁵, F Sourri⁶, N Syrimi⁷, N Lemonakis⁸, E Peskelidou⁹, K Papanastasiou¹⁰, K Souliotis¹¹, A Lourida¹², P Panagopoulos¹³, D Hatzigeorgiou¹⁴, N V Sipsas²

Affiliations

¹ Directorate of Research, Studies and Documentation, National Public Health Organization, Athens, Greece. Electronic address: maltezou.helena@gmail.com.
² Pathophysiology Department, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
³ Department of Health Services Policy and Management, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA.
⁴ First Department of Paediatrics, University of Athens, Aghia Sophia Children's Hospital, Athens, Greece.
⁵ Infection Control Committee, Laiko General Hospital, Athens, Greece.
⁶ Department of Infection Control, 251 Hellenic Air Force General Hospital, Athens, Greece.
⁷ Department of Infection Control, 251 Hellenic Air Force General Hospital, Athens, Greece; Paediatric Department, 251 Air Force General Hospital, Athens, Greece.
⁸ Infection Control Committee, University Hospital of Alexandroupolis, Alexandroupolis, Greece.
⁹ COVID-19 Intensive Care Unit, 424 General Military Hospital of Thessaloniki, Thessaloniki, Greece.
¹⁰ Operating Rooms, 424 General Military Hospital of Thessaloniki, Thessaloniki, Greece.
¹¹ Faculty of Social and Political Sciences, University of Peloponnese, Corinth, Greece; Health Policy Institute, Athens, Greece.
¹² Infection Control Committee, Aghia Sofia Children's Hospital, Athens, Greece.
¹³ Second Department of Internal Medicine, Medical School, Democritus University of Thrace, Alexandroupolis, Greece.
¹⁴ Medical Directorate, Hellenic National Defence General Staff, Athens, Greece.

Abstract

Aim: To estimate the incidence, timing and severity of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) breakthrough infections in fully vaccinated healthcare personnel (HCP).

Methods: In total, 6496 fully vaccinated HCP were analysed prospectively from 15^th November 2021 to 17^th April 2022. Full coronavirus disease 2019 (COVID-19) vaccination was defined as a complete primary vaccination series followed by a booster dose at least 6 months later.

Results: Overall, 1845 SARS-CoV-2 breakthrough infections occurred (28.4 episodes per 100 HCP), of which 1493 (80.9%) were COVID-19 cases and 352 (19.1%) were asymptomatic infections. Of the 1493 HCP with COVID-19, four were hospitalized for 3-6 days (hospitalization rate among HCP with COVID-19: 0.3%). No intubations or deaths occurred. SARS-CoV-2 breakthrough infections occurred at a mean of 16.2 weeks after the last vaccine dose. Multi-variable regression analyses showed that among the 1845 HCP with a breakthrough infection, the administration of a COVID-19 vaccine dose ≥16.2 weeks before the infection was associated with increased likelihood of developing COVID-19 rather than asymptomatic SARS-CoV-2 infection [odds ratio (OR) 1.58, 95% confidence interval (CI) 1.01-2.46; P=0.045] compared with administering a vaccine dose later. The likelihood of developing COVID-19 compared with asymptomatic infection increased by 7% weekly after the last COVID-19 vaccine dose (OR 1.07, 95% CI 1.03-1.11; P=0.001).

Conclusion: SARS-CoV-2 breakthrough infections are common among fully (boosted) vaccinated HCP. However, full COVID-19 vaccination offered considerable protection against hospitalization. These findings may contribute to defining the optimal timing for booster vaccinations. More efficient COVID-19 vaccines that will also confer protection against SARS-CoV-2 infection are needed urgently.

Keywords: Booster dose; Breakthrough infection; COVID-19; Healthcare personnel; SARS-CoV-2; Vaccination.

MeSH terms

Asymptomatic Infections
Breakthrough Infections
COVID-19 Vaccines*
COVID-19* / epidemiology
COVID-19* / prevention & control
Delivery of Health Care
Humans
SARS-CoV-2
Vaccination

Substances

COVID-19 Vaccines

Supplementary concepts

COVID-19 breakthrough infections