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

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

H C Maltezou  1 , M N Gamaletsou  2 , T V Giannouchos  3 , D-M Koukou  4 , A Karapanou  5 , F Sourri  6 , N Syrimi  7 , N Lemonakis  8 , E Peskelidou  9 , K Papanastasiou  10 , K Souliotis  11 , A Lourida  12 , P Panagopoulos  13 , D Hatzigeorgiou  14 , N V Sipsas  2
Affiliations

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

H C Maltezou et al. J Hosp Infect. 2023 Feb.

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 15th November 2021 to 17th 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.

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Figures

Figure 1
Figure 1
Cumulative episodes of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) breakthrough infections among 6496 fully vaccinated healthcare personnel by time since last coronavirus disease 2019 (COVID-19) vaccine dose. Blue line, breakthrough SARS-CoV-2 infections; red line, COVID-19 cases; green line, asymptomatic infections.
See this image and copyright information in PMC

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