Table 3.

Suggested reasons for the variable incidence of post-vaccination infection in the healthcare workers.

S. No.	VARIABLES	RELEVANCE
I)	PATHOGEN RELATED
	Virulence of Virus	Variant of Concern are highly virulent mutants and can bypass the immunity
II)	HOST RELATED
	Age profile	Increasing age is a risk factor of acquiring infection and more severe
	Comorbidities	Medical comorbidities like Respiratory disease, Diabetes, Hypertension, Obesity, Immuno-compromised conditions are identified high risk factors
	Immunity level	Higher immunity is present in individuals with a history of prior COVID-19 disease, and post vaccination (especially after two weeks of the 2nd dose)
	Asymptomatic cases	Routine and random testing for SARS-COV-2 infections can pick up asymptomatic infections, which will add to the total number of cases
III)	VACCINE RELATED
	Number of vaccination	Although some immunity is achieved after the 1st dose of vaccination, a higher degree of protection is achieved after two doses
	Vaccine efficacy	Most used vaccines globally, have shown high degree of safety, protection and prevention from severe disease in case of post-vaccination infection
IV)	STUDY RELATED
	Study period	If the study is done during the period of an ongoing COVID ‘wave’, the incidence would be higher
	Geographical location	If the study location falls in the area of higher SARS-COV-2 infections, there would be higher rate of infection in the healthcare workers also
	Type of hospital	A COVID dedicated hospital is likely to have higher incidence of infections in the healthcare workers
	Single or Multi centre study	A multi-centre study provides more heterogeneous data and better projection of the incidence and outcomes of the infections
	Sample size	Larger the sample, better inferences can be derived