Post-vaccination incidence and side effects of COVID-19 in a cohort of Brazilian healthcare professionals: an internet-based survey

Abstract Objective So far, at least 18 different severe acute respiratory syndrome coronavirus-2 vaccines have been approved. Until October 2022, 12.8 billion doses had been administered all over the world. Vaccination of high-risk groups and healthcare professionals was initially prioritized. This cross-sectional survey aimed to investigate the occurrence of vaccine side effects, as well as the incidence of COVID-19 among vaccinated healthcare professionals. Methods A survey was structured and shared with healthcare professionals using a digital platform to collect data between May and June 2021. Results This study included 6,115 participants. The most prevalent age group was 30-39 years (31.3%), 67.3% were female and 73.2% accounted for physicians, and nearly half worked in frontline care for COVID-19. Approximately, two-thirds of them were vaccinated with CoronaVac, and about 60% reported at least one side effect following the vaccination. Nevertheless, minor reactions were more frequent, such as pain at site of injection, fatigue, and headache. Our data could be used to inform people on the likelihood of side effects of COVID-19 vaccines, particularly CoronaVac, since this is the largest study about vaccine reactions using this vaccine, to our best knowledge. Conclusion The incidence of side effects in Brazilian healthcare professionals was 60%, and the most common side effects included local swelling/pain, fatigue/tiredness, fever, headache, and limb pain.


❚ INTRODUCTION
Since the first reports in Wuhan (Hubei province, China) on December 31, 2019, coronavirus disease 2019 (COVID-19) has posed unprecedented challenges to the world. (1) The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified as the pathogenic agent of COVID-19. Until June 2022, the virus infected over 547 million individuals and caused more than 6.3 million deaths worldwide. (2,3) On December 2 nd , 2020, the United Kingdom gave temporary regulatory approval for the Pfizer/BioNTech vaccine, and was the first region to approve COVID-19 vaccination in the Western world. On December 31, 2020, the World Health Organization (WHO) listed the BNT162b2 COVID-19 mRNA vaccine einstein (São Paulo). 2022;20:1-11 for emergency use, making the Pfizer/BioNTech vaccine the first to receive emergency validation. (4) Concomitant with the further development of vaccines, the WHO has strongly recommended intensive vaccination programs all over the world.
Since then, at least 18 different vaccines have been approved and until October 2022, 12.8 billion doses were administered throughout the world. (5) Vaccination strategies varied in all continents. Due to the increased viral exposure at the workplace and higher risk of developing severe diseases, healthcare professionals have been given priority. In Brazil, four types of vaccine (CoronaVac-Butantan/Sinovac; ChAdOx1-Oxford/ Astrazeneca; Ad26.COV2 S-Janssen; and BNT162b2/ Pfizer/BioNTech) received governmental approval and registration. (3,6) Several adverse reactions due to vaccination have been reported. Both active component (antigen) and other vaccine components (adjuvants) can cause hypersensitivity and anaphylaxis, which is the most severe hypersensitivity reaction. The incidence rate of anaphylaxis before COVID-19 was approximately 1.31 per million vaccine doses. (7) The proinflammatory cytokines interleukin 1 and 6 and tumor necrosis factor α are released in response to vaccination, causing pain at the injection site by inducing inflammation. Additionally, they may cause systemic symptoms, such as headache, fatigue, malaise, nausea, and fever, which are similar to symptoms of some infectious diseases, including COVID-19. (8) Most of the major vaccine reactions are compulsorily notified; however, minor reactions, such as headache and myalgia, are usually underreported. (3,6,9) To the best of my knowledge, this is the largest study published about adverse effects of CoronaVac-Butantan/Sinovac vaccine.

❚ OBJECTIVE
To investigate the occurrence of vaccine side effects, as well as the incidence of COVID-19 among vaccinated healthcare professionals.

❚ METHODS Study design
This was a cross-sectional study with data gathered by means of an internet survey. The questionnaire was structured and shared using the digital platform Google Forms™.
The survey respondents were invited to take part in the study through different online platforms. The survey link was promoted through e-mail communications and social media (Facebook™, e-mail and WhatsApp™).
The questionnaire was designed in a user-friendly layout, with clear answering instructions that required only minimal computer/smartphone skills to navigate and complete. The survey link was shared on May 16, 2020, and the responses were collected until June 7, 2021. Participation was voluntary and included informed consent and anonymity; hence, no personal information was collected, and respondents could not be identified.
At the time of survey, the Brazilian government adopted massive vaccination of health professionals with multiple vaccines available, mainly CoronaVac. The questionnaire was self-administered in Portuguese and is described in appendix 1.

Data analysis
The online response submitted by respondents was transferred to an Microsoft Excel database and exported to SPSS version 21.0 for analysis. Fisher´s exact test was used to compare means of selected background variables. Bivariate and multivariate logistic regression analyses were used to compare the groups and to predict the relations between dependent and independent variables. A 95% confidence interval (95%CI) and a p<0.05 were used to determine a statistically significant association.

❚ RESULTS
A total of 6,115 healthcare professionals responded to the online questionnaire and were included in the study; no response was excluded. The most prevalent age group was between 30-39 years (31.3%), with a predominance of females (67.3%).
About 60% had symptoms after the vaccine and the most prevalent side effects were pain at site of injection (34.8%), fatigue (21.5%) and headache (22.6%). Approximately, half had the symptoms until three days after vaccination, whereas 3,188 (52.1%) had symptoms after the first vaccine dose, and 2,412 (39.6%) had the symptoms after the second dose. Additionally, 834 (13.6%) participants did not take the second dose at the time of the survey (Table 3). Northeast 918 (15) Almost one third of them (30.5%) reported being diagnosed as COVID-19 before the vaccination, whereas 1.8% developed reinfection despite immunization ( Table 2). The incidence of post-vaccine infection (professionals previously vaccinated who were infected with COVID-19) was 4.9%, whereas 5.7% received CoronaVac and 3.3% ChAdOx1.

Multivariate analysis
In the multivariate logistic regression analysis, use of CoronaVac vaccine, male sex, age under 40 years and having comorbidities use of CoronaVac vaccine, male sex, age under 40 years and having comorbidites were independently associated with developing postvaccination symptoms. CoronaVac vaccine was the strongest factor associated with post-vaccination symptoms followed by male sex, both with more than double odds. On the other hand, working on the COVID-19 frontline, reinfection and having COVID-19 post-vaccination were factors not associated with post-vaccination symptoms. (Table 4) Vaccine efficacy varies; however, it reduces mortality and cases of severe disease depending on the type of vaccine and characteristics of the vaccinated population. (13) Vaccine effectiveness is the percentage reduction of disease cases in a vaccinated group of people compared to an unvaccinated group. COVID-19 efficacy is measured by the development of disease or severe illness and death by COVID-19. (14) The efficacy of CoronaVac (administered in 64% of participants) in a large phase III trial in Brazil showed that two doses, at an interval of 14 days, had an efficacy of 51% against symptomatic COVID-19 infection, 100% against severe COVID-19, and 100% against hospitalization, starting 14 days after the second dose. (15) Another phase III clinical trial published showed efficacy to prevent COVID-19 infection using BNT162b2 of 95%, (16) Moderna of 94.1%, (17) ChAdOx1 of 70.40% (18) and Gam-COVID-Vac of 91.6%. (18,19) The present retrospective survey and bivariate analysis revealed professionals who received CoronaVac had an approximately 80% higher risk of post-vaccination infection (RR=1.78; 95%CI: 1.37-2.31; p<0.0001), and only 15 (5%) were admitted to hospital. The age group was not associated with suffering from COVID-19 after vaccine (p=0.592).
Data about COVID-19 vaccine adverse effects are heterogeneous due to vaccine diversity. Menni et al., (20) in a prospective observational study, followed up 627,383 individuals immunized with BNT162b2 and ChAdOx1 COVID-19 vaccines. Among those vaccinated, 159,101 (25.4%) reported having one or more systemic adverse effects, whereas 257,209 (66.2%) of 388,430 reported one or more local adverse effects. The most commonly reported systemic side effects included fatigue and headache, within the first 24 hours after vaccination and lasted a mean of 1.01 days. Tenderness and pain in the injection site were the most frequently reported local effects occurring on the day after injection and lasting a mean of 1.02 days. The comparison of systemic effects after one dose of each vaccine revealed significantly higher reactogenicity in individuals who had one dose of the ChAdOx1 vaccine than in those who had one dose of the BNT162b2 vaccine (p<0.0001). Other side effects included allergic skin reactions, such as skin burning, rashes and red welts on the lips and face, and were reported by 10,860 (1.7%) out of 627,383 users regarding both types of vaccine, but none was severe.
The minor to moderate side effects of Pfizer-BioNTech vaccine in 455 Saudi Arabian inhabitants, in a retrospective online survey, revealed 98.4% complained of symptoms, mostly injection site pain, headache, flu-like symptoms, fever and fatigue. (21)

❚ DISCUSSION
Since the start of vaccine production, people have expressed worries about hazards and risks of getting vaccined, often caused by misinformation. These movements led the WHO to consider vaccine hesitancy as one of top ten threats to global health. (10) Currently, massive vaccination is the main strategy to control the COVID-19 pandemic and is supported by the WHO (11) and the United States Food and Drug Administration (FDA). (12) Our study included 3,911 (64%) health professionals who were vaccinated with CoronaVac and, to our best knowledge, this is the largest phase IV study on adverse events of CoronaVac.
Our study found approximately 60% of adverse effects, whereas Kaya et al., who conducted a prospective study with 329 health professionals vaccinated with CoronaVac in Turkey, found adverse effects in only 33.2% of participants (including pain, redness, swelling, headache fever, state of sleep/fatigue, nausea/vomiting, allergy, extensive pruritus and myalgia). The three most common severe adverse reactions were headache, state of sleep/fatigue, pain and redness. (22) Another study from Turkey with 780 healthcare workers (cross-sectional study) showed 62.5% of professionals experienced at least one adverse effect, and injection site pain was the most frequent (41.5%), and fatigue (23.6%), headache (18.7%), muscle pain (11.2%) and joint pain (5.9%) were the common systemic adverse effects. Female workers were significantly more often affected (67.9%). (23) ❚ CONCLUSION The incidence of side effects in our sample of vaccinated Brazilian healthcare professionals was high, and the most common side effects were local swelling/pain, fatigue/tiredness, fever, headache, and limb pain. The incidence of side effects with CoronaVac was much lower than in previous publications with this vaccine, probably due to the short time between the vaccine and the survey, but higher than with other vaccines. Our data could be used to inform people on the likelihood of side effects of COVID-19 vaccines, particularly CoronaVac, since this is the largest study with vaccine reaction using this vaccine, to our best knowledge.