SARS-CoV-2 Antibody Response Following COVID-19 Vaccination, a Longitudinal Study

Background

The objective was studying the antibody response following immunization with COVID-19 vaccines.

Material and Methods

It was a longitudinal study of healthcare workers (HCWs). Two groups were taken, Group 1 had taken first dose of the COVID-19 vaccine, at least 3 weeks have passed. Group 2 had taken two doses of COVID-19 vaccine and at least 2 weeks have passed. A quantitative test for antibodies to SARS-CoV-2 spike protein was done. Follow-up of both groups was done after 3 months of collection of the first sample.

Results

The antibody titre of the 57 HCWs in Group 1, decreased significantly 125 days after the first dose [median = 2,013 U/ml] as compared to the titre 30 days after the first dose of Covishield vaccine[median = 9,965.26 U/ml]. The median interval between two doses of vaccine was 34 days. In Group 2, the antibody titre of the 60 HCWs in Group 2, decreased significantly 114 days after second dose[median = 1,411 U/ml] as compared to the titre 19.5 days after second dose of Covishield vaccine [median = 2,377.5]. There was no significant difference in the antibody titre in follow-up samples of HCWs with and without side effects.

Conclusion

The antibody titre decreases after 13 to 17 weeks post the second dose of Covishield vaccination. The decision of the Government of India to increase the interval between two doses of Covishield is justified. Low antibody titre can be the reason for breakthrough infections. The antibody titre was not related to side effects post-vaccination.

Assessment of Risk Factors for COVID-19 in Health Care Workers: A Nested Case-Control Study

OBJECTIVES

To study the risk factors for SARS-CoV-2 infection in health care workers (HCWs) exposed to COVID-19 patients.

MATERIAL AND METHODS

This was a nested case-control study of health care workers(HCWs) in a Dedicated COVID Hospital(DCH). The data collection was done from Dec 2020 to Feb 2021. The study was part of an international multicenter study by the World Health Organisation (WHO).2 The Doctors, nurses, housekeeping staff, clerks, and other staff working in this DCH were considered as HCWs. HCWs working in this DCH with confirmed COVID-19 were recruited as cases and other HCWs working in this DCH in the same Ward/ICU/office without infection were recruited as controls (incidence density sampling). Three controls were taken per case. The questions were in the Likert scale.

RESULTS

There were 25 cases and their 75 controls. There was no significant difference between cases and controls with respect to age, sex, occupation, education, and comorbidities and all controls were negative for antibodies at the time of the interview. Most (70%) of the HCWs were doctor by profession followed by nurses (19%). All HCWs were trained in IPC (infection Prevention and Control). Most (96%) HCWs reported that PPE (personal protective equipment) is available in sufficient quantity. There was no significant difference between cases and controls with respect to those having direct contact with the patient's materials, surroundings, and following hand hygiene.

CONCLUSION

Adequate availability of PPE, IPC training of HCWs are important for preventing COVID-19 but do not completely reduce risk among HCWs.