Highlights•

Vaccines are able to reduce the infection and severity of COVID-19.

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There is a possibility of infection after vaccination against COVID-19.

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The diagnosis of COVID-19 in the past reduced the prevalence of new infections.

Abstract

Introduction: The quick spread of SARS-CoV-2 led to the development of vaccines that are capable of reducing infection and the number of more severe COVID-19 cases. Aim: To assess COVID-19 prevalence among health care workers (HCWs) after vaccination against SARS-CoV-2. Methods: Cross-sectional study on the prevalence of COVID-19 diagnosis among 7.523 HCWs vaccinated against SARS-CoV-2 with Coronavac and ChAdOx1 nCoV-19 in a university hospital, in southern Brazil, between January 18, 2021 and March 18, 2021.The variables evaluated were: sex, age, work area, role, source of infection, previous diagnosis of COVID-19, date of vaccine administration, type of vaccine, and need for hospitalization. The statistical analysis used Poisson regression and Fisher's Exact Test with the SPSS software version 25 and level of significance set at 5%. Results: 813 vaccinated HCWs showed symptoms suggestive of COVID-19, and 35.4% (288) who underwent RT-PCR for SARS-CoV-2 had a detectable result. There was a reduction of 62% in new cases of COVID-19 among HCWs in the institution after seven weeks of the start of the vaccine rollout. Conclusion: Our data suggest that the vaccines used by the institution reduced the number of COVID-19 cases among health care workers, showing the effectiveness of the vaccines.

KeywordsIntroductionThere is evidence that vaccines are able to reduce infection and the number of more severe cases of COVID-19 (Bradley T,et al.,2021; Keehner J, et al.,2021; Daniel W, et al,2021; Benenson S, et al.;2021). The P1 variant of SARS-CoV-2 is refractory to multiple neutralizing monoclonal antibodies (Wang P, et al., 2021). This may lead to antigen alterations that impair vaccine protection, leading to a diagnosis of infection in individuals in whom vaccine efficacy was evidenced (Wang P, et al.,Wang et al., 2021Wang P Casner RG Nair MS Wang M Yu J Cerutti G Increased resistance of SARS-CoV-2 variant P.1 to antibody neutralization.).Methods

A cross-sectional study on the prevalence of COVID-19 diagnosis was conducted among 7.523 health care workers (HCWs) vaccinated against SARS-CoV-2 with Coronavac, inactivated virus vaccine, and ChAdOx1 nCoV-19, using chimpanzee adenovirus as a viral vector for the expression of the SARS-CoV-2 Spike protein, in a university hospital in southern Brazil. 4.260 HCWs received Coronavac (3.676 with two doses and 584 with only one dose) and 3.263 received one dose of ChAdOx1 nCoV-19 between January 18, 2021 and March 18, 2021.It was found that 813 health professionals with symptoms suggestive of COVID-19 performed an RT-PCR (reverse transcriptase reaction followed by a polymerase chain reaction) test for SARS -CoV-2 and received at least one dose of the SARS- CoV-2 vaccine in the first nine weeks of vaccination.

The variables evaluated were: sex, age, work area, role, source of infection, previous diagnosis of COVID-19, date of vaccine administration, type of vaccine (ChAdOx1 nCoV-19 and Coronavac), date and result of the RT-PCR assay for SARS-CoV-2, number of professionals diagnosed with COVID-19 after vaccination, need for hospitalization and in the Intensive Care Unit (ICU).

Prevalence Ratio (PR) measure with 95% CI, estimated by the Poisson Regression analysis with robust variance adjustment, was used to verify the factors and the strength of the association with the PCR test result in the general sample and stratified by type of vaccine, and Fisher's exact test was used for the association of the vaccine with the hospitalization and ICU outcomes among COVID-19 patients. Analyses were performed using the SPSS software version 25, and the level of significance was set at 5%.

The study was approved by the Research Ethics Committee of the institution under number 3080132400005327, and financial support was provided by the Research Incentive Fund (FIPE) of Hospital de Clinicas de Porto Alegre.

ResultsThe 20-40 and 41-60 age groups were represented similarly in our sample, that is, 48% and 48.6%, respectively, of the total of HCWs evaluated. 81.7% of the 813 HCWs evaluated were females, and 35.4% (288) of those who underwent RT-PCR for SARS-CoV-2 showed a detectable result. (Table 1).

Table 1Demographic of Vaccinated HCWs with symptoms suggestive of COVID-1 (N=813).

* Without patient assistance: jobs that do not require contact patients (Baptista MC, et al., Baptista et al., 2021Baptista MC Burton WN Pawlecki B Pransky G. A Physician's Guide for Workers' Return to Work During COVID-19 Pandemic.).

** Non COVID care: assistance to patients without a diagnosis of COVID-19.

***COVID-19 care: assistance to patients diagnosed with COVID-19.

****Other health professionals with higher education.

The diagnosis of COVID-19 in the past reduced the prevalence of new infections by 68% (PR: 0.32 95% CI: 0.19 – 0.56). A similar result was observed with the ChAdOx1 nCoV-19 vaccine, with a decrease in infection prevalence of 22% (PR: 0.78 95% CI: 0.64 – 0.96). After the first dose, infection prevalence decreased by 7% every week (PR: 0.93 95% CI: 0.89 – 0.97) regardless of the type of vaccine.

Among the 314 suspected cases who had received the ChAdOx1 nCoV-19 vaccine, a positive diagnosis for COVID-19 was observed in 30.3%. An important finding was that a previous diagnosis of COVID-19 over 45 days ago reduced prevalence by 71% (PR: 0.29 95% CI: 0.11 – 0.75) among those professionals. When only professionals who received one dose of ChAdOx1 nCoV-19 were considered, prevalence was reduced by 10% each week after vaccination (PR: 0.90 95% CI: 0.84 – 0.96) (Table 2).

Table 2Factors associated with the diagnosis of COVID-19 - Vaccinated with Coronavac and ChAdOx1 nCov-19.

*Without patient assistance: jobs that do not require contact with patients.

** Non COVID patient assistance: assistance to patients without a diagnosis of COVID-19.

*** COVID patient assistance: assistance to patients diagnosed with COVID-19. ****Other health professionals with higher education.

Among the 399 suspected cases who had received the Coronavac vaccine, a positive diagnosis for COVID-19 was observed in 38.7%. Physicians showed a 2.25-fold increased prevalence compared to other health professionals with higher education for a positive diagnosis of COVID-19 (PR: 2.25 95% CI: 1.08 – 4.69). A previous diagnosis of COVID-19 reduced prevalence by 65% (PR: 0.35 95% CI: 0.18 – 0.67) (Table 2).

The hospitalization outcome was observed in 14 of 288 COVID-19 patients. However, no cases with positive RT-PCR died after the administration of both vaccines during the period under study.

Discussion

Our data suggest that, after the first dose, the prevalence of infection decreased every week, regardless of the type of vaccine. ChAdOx1 nCoV-19 seems to provide, within our population, a better protective factor in relation to COVID-19, and further studies are needed to identify the cause of this difference.

The higher prevalence among physicians, identified in our population, may be associated with the prevalence of double working hours, with different levels of exposure and protection against COVID-19.

The different levels of protection against COVID-19, such as the use of personal protective equipment, may be associated with a lower prevalence of positive cases in the occupational environment when compared to other environments. However, more studies are needed.

The presence of a previous diagnosis of COVID-19 was a protective factor against new SARS-CoV-2 infections. In agreement with our data, a Danish study and a study conducted in Qatar pointed out that the presence of a previous diagnosis of COVID-19 infection can provide up to 78.8% and 95 % of protection against a new infection (Hansen CH, et al.,Hansen et al., 2021Hansen CH Michlmayr D Gubbels SM Mølbak K Ethelberg S. Assessment of protection against reinfection with SARS-CoV-2 among 4 million PCR-tested individuals in Denmark in 2020: a population-level observational study.; Abu-Raddad LJ, et al.,2021).

Our data, as well as that of the study conducted in Israel evidenced a decline in cases of COVID-19 and in the severe forms of the disease following the start of the vaccine rollout (Rossman, H, et al.,2021).

Conclusion

Our data suggest that the vaccines used by the institution reduced the number of COVID-19 cases among HCWs and protected against severe forms of the disease.

The analysis of the cases with SARS-CoV-2 positive RT-PCR shows that there is a possibility of infection after the administration of the COVID-19 vaccine. Further studies are needed to confirm this estimate in the medium and long term, taking into account the types of viruses that circulate in the country and also the type of vaccine administered.

The study was approved by the Research Ethics Committee of the institution under number 3080132400005327, and financial support was provided by the Research Incentive Fund (FIPE) of Hospital de Clínicas de Porto Alegre.

The researchers declare that they have no conflicts of interest.

Uncited References:Abu-Raddad et al., 2021Abu-Raddad LJ Chemaitelly H Coyle P Malek JA Ahmed AA Mohamoud YA et al.SARS-CoV-2 antibody-positivity protects against reinfection for at least seven months with 95% efficacy., Benenson et al., 2021Benenson S Oster Y Cohen MJ Nir-Paz R. BNT162b2 mRNA COVID-19 Vaccine Effectiveness among Health Care Workers., Bradley et al., 2021Bradley T Grundberg E Selvarangan R LeMaster C Fraley E Banerjee D et al.Antibody Responses after a Single Dose of SARS-CoV-2 mRNA Vaccine [published online March 23, 2021]., Daniel et al., 2021Daniel W Nivet M Warner J Podolsky DK. Early Evidence of the Effect of SARS-CoV-2 Vaccine at One Medical Center [published online March 23, 2021]., Hacisuleyman et al., 2021Hacisuleyman E Hale C Saito Y Blachere NE Bergh M Conlon EG et al.Vaccine Breakthrough Infections with SARS-CoV-2 Variants [published online April 21, 2021]., Keehner et al., 2021Keehner J Horton LE Pfeffer MA Longhurst CA Schooley RT Currier JS Abeles SR Torriani FJ SARS-CoV-2 Infection after Vaccination in Health Care Workers in California., Rossman et al., 2021Rossman H Shilo S Meir T Gorfine M Shalit U Segal E COVID-19 dynamics after a national immunization program in Israel [published online April 19, 2021].Declaration of Competing Interests

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.

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Cell Host Microbe. S1931-3128: 00183-00189Article InfoPublication History

Accepted: July 9, 2021

Received in revised form: July 8, 2021

Received: May 16, 2021

Publication stageIn Press Journal Pre-ProofIdentification

DOI: https://doi.org/10.1016/j.ijid.2021.07.025

Copyright

© 2021 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.

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