COVID-19 after vaccination is a consequence of multiple factors, including the variable vaccine efficacy and the emergence of new viral variants. Sixteen cases of infection after completing the primary series of vaccination in healthcare workers (HCWs) are described. Ten cases had symptoms, mainly loss of smell (four cases), cough (four cases), fever (two cases), nasal discharge or obstruction (three cases), general malaise (two cases), and dyspnea and loss of taste in one case each. The median time between the second dose of the primary vaccination and the positive severe acute respiratory syndrome coronavirus 2 polymerase-chain reaction (PCR) was 132.5 days, and the median cycle threshold value at the time of diagnosis was 25.1. Laboratory tests performed at diagnosis showed results mostly in normal parameters, and in 10 cases, pulmonary findings suggestive of COVID-19 were described. The clinical course of the disease was satisfactory, without complications or sequelae at discharge.

COVID-19 after vaccination in HCWs was mild, with a favorable course of the disease.

The vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) constitutes a fundamental resource to control the current pandemic, and various vaccines are in use and in the pipeline (1). In general, the evidence suggests that the efficacy of the vaccines is in the prevention of severe symptomatic disease, but there is limited evidence about the durability of the immune protection (2). It has been described that after natural infection, the immunological memory remains at least for 6 months (3).

Healthcare workers (HCWs) all over the world were prioritized for the vaccination because of the high risk of infection and the well-known impact on the health workforce (4–6). Gomez Ochoa et al. in a systematic review and meta-analysis reported 11% of HCW with COVID-19 and 5% developed severe disease (5). Additional consequences were observed in psychological well-being and staff retention among others.

Vaccination becomes a highly effective measure for minimizing the adverse consequences of the disease. Nevertheless, post-vaccination SARS-CoV-2 infections were observed and probably related to multiple factors, including the variable vaccine efficacy and the emergence of new viral variants (7–10).

In a COVID-19 dedicated facility in Western Qatar, the vaccination program of 930 HCWs (physician, nurses, and technologists) started in December 2020 with either Pfizer or Moderna vaccine. The surveillance of SARS-CoV-2 infection in HCWs, with data kept after vaccination, included daily temperature monitoring, reporting of symptoms, and contact tracing of exposures, and a monthly mandatory SARS-CoV-2 polymerase-chain reaction (PCR) or antigen test. Positive antigen test results were confirmed by PCR. During the period from December 2020 to August 2021, 16 vaccinated HCWs with COVID-19 were reported. The cases are described in this report.

Out of 930 HCWs (physicians, nurses, and technologists) vaccinated during the period from December 2020 to August 2021, COVID-19 was confirmed by positive PCR post-vaccination in 16 cases (1.7%): 2 male and 14 female cases. All cases received the primary vaccination (two doses). The median age was 45.5 years (minimum 29, maximum 60, and interquartile range 14.5). Five cases had a previous history of chronic conditions, mainly hypertension (HBP) and diabetes mellitus (Table 1). During the study period, the Delta and Alpha variants of SARS-CoV-2 were predominant in the country.

The cases were diagnosed because of the periodic lab test done in asymptomatic cases (6 HCW) or symptoms (10 cases). The most frequent symptoms at the time of diagnosis were loss of smell (four cases), cough (four cases), fever (two cases), nasal discharge or obstruction (three cases), general malaise (two cases), and dyspnea and loss of taste in one case each.

The median time between the second dose of primary vaccination and the positive PCR was 132.5 days (minimum 59, maximum 211, and interquartile range 91). The median cycle threshold (CT) value at the time of diagnosis was 25.1 (minimum 17.3, maximum 35.4, and interquartile range 7.3). After 10 days of the initial positive PCR, the test became negative or inconclusive in nine cases and reactive (CT ≥ 30) in five cases, and in two cases, the values were positive (CT values are 27.86 and 24.16).

Laboratory tests performed at diagnosis showed results mostly in normal parameters, including white blood cell count (median 6.4 × 103/L; minimum-maximum: 3.7-11.6), absolute neutrophil count (3.5 × 103/L; 0.6–8.7), lymphocyte count (1.8 × 103 × 103/L; 1.0–2.7), serum creatinine (59 µmol/L; 34–91), alanine transaminase (17.5 U/L; 10–182), aspartate transaminase (17.5 U/L; 10–89), and lactate dehydrogenase (167.5 U/L; 120–274). D-dimer (0.3 mg/L; 0.2–4.4) was elevated in five cases.

In six cases, the chest X-ray did not show pulmonary findings; in three cases, ground glass images were observed; in six cases, several other lesions (interstitial and inflammatory) were noted; and in one case, the combination of various findings suggested of COVID-19 (case no. 9). Figure 1 shows the maximum oral temperature with descending values during the first 10 days after confirmation, without differences between cases with/without antibiotics.

The most frequent treatment was an antiviral (favipiravir) (13 cases), and antibiotics (amoxicillin-clavulanic acid or azithromycin) were prescribed in five cases. The clinical course of the disease was satisfactory, with no complications or sequelae at discharge.

Regardless of the number of HCWs confirmed with COVID-19 after vaccination, which could be an expression of immune system failure, the clinical picture suggests a more benign disease in comparison with non-vaccinated SARS-CoV-2 infections. The current protocol recommends the use of antiviral drugs, but the requirement of antibiotics, usually prescribed as an empirical and prophylactic approach, could be questioned. The improper use of antibiotics is related to the development of antimicrobial resistance, and the risk of associated healthcare-associated infections adds a significant impact on the cost of healthcare, limited by the global economic crisis generated by the pandemic.

Disease severity changes should be considered an added value of the vaccination. Various papers published report of the findings of mild disease, the limited requirement of medical care, and easy recovery in COVID-19 in HCW after vaccination (7, 8, 10).

In addition, from the infection control point of view, it is important to maintain the staff monitoring system using various methods, involving monitoring of respiratory symptoms and lab tests when necessary, and the requirement of vaccination for the newly hired non-vaccinated staff (and booster doses for those with previous full vaccination). In order to address patient and staff safety, the respiratory protection program, the recommendations for isolation precautions, and the use of personal protective equipment should be reviewed according to the new environments generated by the pandemic.

This report provides evidence, suggesting that COVID-19 after vaccination of HCWs is a mild disease with a good prognosis. Moreover, there is need to strengthen the infection control program focused on patient and staff safety and transmission prevention in healthcare facilities.