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 Table of Contents  
Year : 2022  |  Volume : 24  |  Issue : 2  |  Page : 154-158

COVID-19 breakthrough infections amongst ChAdOx1 nCoV-19 (Covishield) vaccinated health-care workers and its clinical manifestations: A prospective observational study

1 Department of Medicine, INS India, New Delhi, India
2 Department of Gynaecology, NH Powai, Mumbai, Maharashtra, India
3 Department of Medicine, INHS Kalyani, Visakhapatnam, Andhra Pradesh, India

Date of Submission18-Feb-2022
Date of Decision28-Feb-2022
Date of Acceptance07-Mar-2022
Date of Web Publication10-Aug-2022

Correspondence Address:
Surg Lt Cdr (Dr) Vaidehi Thakur
Department of Gynaecology, NH Powai, Mumbai, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmms.jmms_26_22

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Introduction: Second wave of the COVID -19 pandemic had a significant impact on India with large number of populations getting affected by it. Pan -India COVID -19 vaccination was started on 16 January 2021. All the hospital Health Care Workers (HCWs) started receiving Covishield vaccine. By March 2021, all the HCWs received 02 dosages of the vaccine. It was the time when the second wave of COVID-19 started in India. This study was conducted to investigate the occurrence and severity of breakthrough COVID -19 infection (BCI) amongst fully vaccinated HCWs. Materials and Methods: This prospective observational study was conducted at a single multispecialty COVID-19 dedicated hospital on fully vaccinated HCWs who developed BCI. A total of 981 HCWs were enrolled and observed them for six months from March -September 2021 for occurrence of BCI. The outcome measures included percentage of fully vaccinated HCWs developing BCI. The BCI according to various demographic variables was studied. Clinical profile, duration between last dose of vaccine and BCI and requirement of mechanical ventilation were analysed. Results: Out of 981 fully vaccinated HCWs, 97 developed BCI. Amongst one -fifth of them were asymptomatic. Fever and cough were the prominent symptoms. Two HCWs developed COVID -19 pneumonia. None required oxygen supplementation or mechanical ventilation. There was no death observed amongst these COVID -19 infected HCWs. Discussion: BCI occurred in 9.88% fully vaccinated HCWs. They were primarily minor and did not lead to severe disease. Overall, Covishield prevented severe infection in HCWs, leading to decreased ICU admission and deaths.

Keywords: Breakthrough COVID-19 infections, ChAdOx1 nCoV-19 vaccine (Covishield), health-care workers

How to cite this article:
Kamal D, Thakur V, Chauhan AS. COVID-19 breakthrough infections amongst ChAdOx1 nCoV-19 (Covishield) vaccinated health-care workers and its clinical manifestations: A prospective observational study. J Mar Med Soc 2022;24:154-8

How to cite this URL:
Kamal D, Thakur V, Chauhan AS. COVID-19 breakthrough infections amongst ChAdOx1 nCoV-19 (Covishield) vaccinated health-care workers and its clinical manifestations: A prospective observational study. J Mar Med Soc [serial online] 2022 [cited 2023 Apr 1];24:154-8. Available from: https://www.marinemedicalsociety.in/text.asp?2022/24/2/154/353651

  Introduction Top

The severe acute respiratory syndrome coronavirus -2 (SARS- Cov-2) responsible for the COVID-19 pandemic was first detected in Wuhan Province, China. It had a global spread leading to the COVID-19 pandemic. To mitigate the spread of the disease, the Indian Government rolled out a pan India COVID-19 vaccination program on January 16, 2021, with the ChAdOx1 nCoV-19 vaccine (Covishield) and inactivated coronavirus vaccine (Covaxin). The health-care workers (HCWs) in India were initially enrolled to receive the vaccine in phase 1. Our hospital was also nominated for vaccinating HCWs with the Covishield vaccine. By March 21, all the HCWs received both the dosages of the vaccine.

The country witnessed the onset of the second wave of COVID-19 pandemic at the end of February 2021, with an average of about 10,000 infections per day. The situation progressively worsened in May 2021 when more than 400,000 new cases were detected daily.[1]

Our hospital, a COVID-19 dedicated hospital situated in the Southern part of India, also witnessed the heightened patient load due to the second COVID-19 wave. We started observing the occurrence of breakthrough COVID-19 infections (BCI) amongst the fully vaccinated HCWs. We had a group of 981 Covishield vaccinated HCWs under active and passive surveillance for detection of adverse event due to vaccination.[2] We further continued our active and passive surveillance amongst them for the occurrence of BCI.

  Materials and Methods Top

Study setting and design

This observational study was conducted for 6 months, from March 2021 to September 2021.

Our hospital is a tertiary care COVID-19 dedicated hospital situated in the Southern part of India. Our hospital was nominated as COVID-19 vaccination center and started vaccinating HCWs (doctors, nurses, and paramedical staff) with Covishield vaccine from January 16, 2021. The two dosages of Covishield vaccines were given 4 weeks apart. A total of 981 HCWs who received the vaccine were enrolled for active and passive surveillance for BCI. By March 2021, the hospital witnessed the heightened number of COVID-19 patients in the wake of the second wave of COVID-19 infection. During this time, the hospital also witnessed the onset of BCI amongst these HCWs. Ethical approval was obtained from the ethics and research committee of the hospital for studying the clinical profile of COVID-19 infection amongst these HCWs with BCI.

Inclusion criteria

Age >18 years, HCWs who already received two dosages of Covishield vaccine and developed BCI, as confirmed by reverse transcription–polymerase chain reaction were included in the study.

Exclusion criteria

HCWs who did not receive both dosages of Covishield vaccine, the duration between onset of symptoms and second dose of vaccine <2 weeks were excluded from the study.

(The 2 weeks' time was considered since the full immunity against COVID-19 infection develops after 7–14 days post the second dose of Covishield vaccine).[3],[4],[5],[6]

Surveillance system

All 981 HCWs who received both the dosages of the Covishield vaccine were kept under active and passive surveillance. In case of development of any symptom suggestive of COVID-19 infection such as fever, loss of taste or smell, myalgia, breathlessness, and cough, they were placed in quarantine. These individuals were thoroughly evaluated for evidence of COVID-19 infection. In cases found to be positive for COVID-19 infection, they were treated in-home quarantine or admitted in COVID-19 care centre (CCC) or COVID-19 ward, depending upon the medical condition.

Active surveillance was carried out wherein all HCWs in close contact with COVID-19 patients or with a recent history of travel were thoroughly evaluated for evidence of BCI.

If found positive, they were managed in-home quarantine or CCC, as deemed necessary.

Statistical analysis

The outcome measures in this study included the percentage of fully vaccinated HCWs developing BCI across various demographic variables (sex, profession, and age groups) from March 2021 to September 2021. The statistical analysis was performed using IBM-SPSS version 27 (IBM Corp., New York, USA). Chi-square test was performed to determine the association of breakthrough infection according to various demographic variables (sex, profession, and age). MedCalc software (MedCalc Software Ltd. Ostend, Belgium) was used to calculate the 95% confidence interval (CI) of the proportion and odds ratios and corresponding p values.

Active surveillance – Percentage of HCWs who had a history of recent travel or close contact with infected individuals was analyzed. Percentage of HCWs who were asymptomatic/symptomatic were also analyzed.

Passive surveillance – Percentage of various clinical symptoms in symptomatic HCWs and the duration between the last dose of Covishield vaccine and detection of COVID-19 infection were studied.

Severity of BCI Percentage of HCWs with BCI requiring home quarantine or admission in CCC or COVID-19 ward were calculated. Occurrence of COVID-19 pneumonia or subsequent requirement of oxygen supplementation/mechanical ventilatory support amongst these vaccinates were also studied.

  Results Top

A total of 97 fully vaccinated HCWs were detected with BCI. The duration between the second dose of Covishield vaccine and detection of COVID-19 infections was more than 02 weeks in all of them. The demographic profile according to sex, profession, and age group is given in [Graph 1] and [Graph 2].

Active surveillance of these breakthrough infections revealed that 19.58% of HCWs were completely asymptomatic [Table 1]. In symptomatic patients, fever was the most common symptom (53.58%). Other common symptoms included cough, headache, myalgia, and sore throat. About 7.21% (7) of patients suffered from breathlessness [Graph 3]. They were further evaluated. Two HCWs showed evidence of COVID-19 pneumonia [Figure 1]. None of the infected patients required oxygen supplementation or mechanical ventilation. All the patients recovered, and no mortality was detected amongst them [Table 2].
Figure 1: HRCT Chest of fully vaccinated HCW with breakthrough COVID-19 infection

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Table 1: Active surveillance of breakthrough COVID.19 infection

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Table 2: Management of breakthrough COVID-19

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We assessed the duration between the second dose of COVID-19 vaccination and BCI. 26.8% of patients were detected with breakthrough infection after 70 days of vaccination with second dose [Table 3].
Table 3: Duration between the second dose of COVID-19 vaccination and breakthrough COVID-19 infection

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Association of BCI amongst the fully COVID-19 vaccinated HCWs with various demographic variables (age group, sex, and profession) was determined. We found no significant association of BCI with these demographic variables (P < 0.05) [Table 4].
Table 4: Association of breakthrough COVID-19 infection amongst fully COVID-19 vaccinated health-care workers with age group, sex, and profession

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  Discussion Top

Our hospital started Covishield vaccination amongst HCWs on January 16, 2021. Hospital took massive proactive steps in vaccinating all the HCWs rapidly. By March 2021, all the HCWs received two dosages of the Covishield vaccine. The second wave of COVID-19 started in 2021. As we were already keeping surveillance for the occurrence of adverse events in these HCWs, in view of the second wave of COVID-19 infection, we continued the surveillance amongst these HCWs for the occurrence of BCI. All these 981 HCWs were kept under active and passive surveillance for BCI till September 2021. During this duration, 97 HCWs were detected with BCI. This indicated that during the second COVID-19 wave, about 9.88% of fully vaccinated HCWs developed BCI. This is slightly less than that observed during surveillance in a chronic care medical facility in Delhi, India, (13.2%) where HCWs received either AZD1222 (ChAdOx1-S) or BBV152.[7]

However, it is slightly higher in comparison to another observational study of BCIs amongst Oxford–AstraZeneca COVID-19 vaccinated HCWs in Vietnam, wherein a total of 69 amongst 866 (8%) HCWs were found positive for COVID-19 infection.[8] Another study conducted at Vellore showed 9.6% breakthrough infection amongst fully vaccinated HCWs.[9]

On the evaluation of breakthrough infection amongst different professionals, it was found that 8.6% (8) doctors, 17.5% (7) nurses, and 9.66% (82) paramedical staff developed breakthrough infection. In our study, we detected higher, but statistically not significant incidence of BCI amongst the nurses. Higher incidence might be due to the extended duration of exposure with COVID-19 patients while providing nursing care in comparison to other groups of HCWs. Similar trend was detected in another study where the observer detected higher incidence of BCI amongst nursing staff.[10]

All the HCWs with BCI were extensively evaluated. 19.58% (19) HCWs were found completely asymptomatic. These individuals were detected with BCI when we evaluated close contacts of COVID-19-infected individuals or during the evaluation of individuals with recent history of travel.

Fever was the most common symptom, as it was found in 53.6% (52) HCWs. All the HCWs were extensively monitored and evaluated for COVID-19 pneumonia. Seven HCWs who developed dyspnea underwent an X-ray/computed tomography scan of the chest. The radio imaging of two HCWs showed the features of COVID-19 pneumonia [Figure 1]. All the patients maintained adequate oxygen saturation during infection and recovery, and none of them required oxygen supplementation. These findings were consistent with the vaccine's effectiveness at protecting against severe disease, as suggested in other studies.[11],[12],[13]

Amongst those who acquired BCI, the duration of infection after the second dose of immunization ranged from 15 to 112 days (average: 52.1). We observed the highest rate of BCI during 41–50 days post the second dose of vaccination [Table 3]. This corresponds to roughly the period when the country witnessed the peak of the second wave of COVID-19 infection.[1] The recession in the rate of BCI cases was also noticed during the downfall of the second wave of COVID-19 infection. A similar finding was observed in another study in which maximum occurrence of BCI was detected during the peak of the second COVID wave.[10] In the same study, the average duration between the second dose of vaccination and BCI was 38.4 days, which was less than our study findings.[10] This might be because we conducted this study for almost 6 months post the second dose of vaccination, whereas the researcher in the above study observed only 100 days postvaccination.[10] However, as the maximum incidence of BCIs was detected during the peak wave of COVID-19 infection, it is difficult to state that HCWs acquired higher risk of BCI 41–50 days post-COVID-19 vaccination.

Strengths and limitations

The strengths of the study are that it was conducted in real-world settings with the period of observation of 6 months from March 2021 to September 2021. The majority of HCWs had already received both the dosages of the Covishield vaccine by February 2021, and thus, they were fully vaccinated at the time of onset of the second wave of the COVID-19 pandemic in India. During these 6 months of observational period, these fully vaccinated HCWs were exposed to large-scale viral exposure, while providing outpatient or inpatient health-care services, thus proving the efficacy of vaccines in preventing breakthrough infection. However, there are certain study limitations. First, as we had already observed, about one-fifth of breakthrough infections were completely asymptomatic. We were able to detect them only on the basis of high suspicion. It might be possible that we missed other asymptomatic breakthrough infections during this period. Second, we did not assess the development of protective antibodies amongst the HCWs to categorically state that the breakthrough infection happened despite the availability of adequate protective antibodies. Third, we did not ascertain the comorbidity status amongst HCWs, though the likelihood of underlying comorbidities in the HCWs was less considering their low median age. Finally, the sample size was not adequately powered to detect a statistically significant difference in the occurrence of BCI across the different subgroups.

  Conclusions Top

In our study, we found about one in ten fully Covishield vaccinated HCWs developed BCI during the second COVID-19 wave. This suggested a high risk amongst the HCWs for developing BCI. Most of the patients developed mild infections only with no admission in intensive care unit or mortality. As the duration of the study was for 6 months, further study is recommended to know the actual BCI on a long-term basis amongst the fully vaccinated HCWs.


Niyakshi Shah.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Chaudhary SR. India Accounts for 1 in 3 New Covid Cases being Recorded. Here is Its Second Wave in 5 Charts. Health and Science. CNBC; 03 May, 2021. Available from: https://www.cnbc.com/2021/05/03/india-covid-crisis-charts-show-the-severity-of-the-second-wave.html. [Last accessed on 2021 Oct 12].  Back to cited text no. 1
Kamal D, Thakur V, Nath N, Malhotra T, Gupta A, Batlish R. Adverse events following ChAdOx1 nCoV-19 Vaccine (COVISHIELD) amongstst health care workers: A prospective observational study. Med J Armed Forces India 2021;77:S283-8.  Back to cited text no. 2
PTI. Covid Vaccination Voluntary, Antibodies Develop 2 Weeks after Second Dose: AIIMS Director. The Hindu; 06 January, 2021. Health: [about 2 p.]. Available from: https://www.thehindu.com/sci-tech/health/covid-vaccination-voluntary-antibodies-develop-2-weeks after-second-dose-aiims-director/article33504935.ece#. [Last accessed on 2021 Feb 28].  Back to cited text no. 3
World Health Organization. Coronavirus Disease (COVID-19)/Media Resources/Science in 5/Episode #23 – I am Vaccinated, What Next? [Video on internet]; 29 January, 2021. Available from: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/media-resources/science-in-5/episode-23---i-am-vaccinated-what-next. [Last accessed on 2021 Aug 10].  Back to cited text no. 4
Speiser DE, Bachmann MF. COVID-19: Mechanisms of vaccination and immunity. Vaccines (Basel) 2020;8:404.  Back to cited text no. 5
Australian Government. Department of Health: Is It True? How long Does it Take to Have Immunity after Vaccination; 25 August, 2021 Available from: https://www.health.gov.au/initiatives-and-programs/covid-19-vaccines/is-it-true/is-it-true-how-long-does-it-take-to-have-immunity-after-vaccination [Last accessed on 2021 Oct 10].  Back to cited text no. 6
Tyagi K, Ghosh A, Nair D, Dutta K, Singh Bhandari P, Ahmed Ansari I, et al. Breakthrough COVID19 infections after vaccinations in healthcare and other workers in a chronic care medical facility in New Delhi, India. Diabetes Metab Syndr 2021;15:1007-8.  Back to cited text no. 7
Chau NV, Ngoc NM, Nguyet LA, Quang VM, Ny NT, Khoa DB, et al. An observational study of breakthrough SARS-CoV-2 Delta variant infections amongst vaccinated healthcare workers in Vietnam. EClinicalMedicine 2021;41:101143.  Back to cited text no. 8
Victor PJ, Mathews KP, Paul H, Mammen JJ, Murugesan M. Protective effect of COVID-19 vaccine amongst health care workers during the second wave of the pandemic in India. Mayo Clin Proc 2021;96:2493-4.  Back to cited text no. 9
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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]


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