A retrospective study to assess the effectiveness of Covid-19 vaccination and incidence of SARS-COV-2 reinfection in healthcare and frontline workers working in a tertiary cancer centre of India.

Protocol summary This is a retrospective study done to find out the efficacy of the vaccine in healthcare and frontline workers. The healthcare and frontline workers are more prone toSARSCOV-2 infection due to close contact with the patients and also working daily in the hospital where chances of contracting the SARS-COV-2 is very high. There is scarcity of the data regarding the efficacy of the vaccine after 1st and 2nd dose in healthcare and frontline beneficiaries working in oncology centres. We are analyzing a database maintained at our tertiary cancer centre from 25 January to 18 June 2021 of HCW and FLW who were vaccinated in between the stipulated period. The analysis includes the positivity rate after 1st, 2nd dose and without any vaccination. Also, the median number of days of hospitalization required after 1st, 2nd dose and without any vaccination. The data of HCW and FLW who developed reinfection following their recovery and incidence of recurrence will also be analysed.

        Aim & Objectives  Primary objective

To assess the efficacy of vaccines in the prevention of SARS-COV-2 in healthcare and frontline workers. Factors tested were age, gender, type of vaccine taken, number of doses taken, hospitalization required or not & percentage of HCW and FLW positive with vaccination and without vaccination.

Secondary objective

To assess the incidence of SARS-COV-2 reinfection following natural infection.

Study Population

Inclusion criteria

1. Healthcare and frontline workers from a single tertiary cancer centre

2.  HCW and FLW between the age of 18-80 years and willing for the vaccination

Exclusion criteria

1.Non-healthcare care and non- frontline workers

2.Healthcare and frontline workers from other hospitals

         Trial design :Retrospective analysis           Study setting :This study would be a retrospective review of healthcare and frontline workers who were vaccinated for the prevention of SARS-COV-2 infection and also who got reinfected after natural infection in a single tertiary Cancer Centre from India.   Methodology :This is a retrospective study. The vaccination program at our Centre was started from 25th January 2021 and is ongoing. We maintained an excel sheet of the healthcare and frontline workers who were vaccinated at our Centre on a day to day basis. The excel Sheet contains the ID number, name, age, gender, type of the vaccine given, date of the first vaccine taken, date of the second vaccine given, date of positivity after 1st dose of vaccine, date of positivity after 2nd dose of the vaccine, positivity in non-vaccinated people after the start of vaccination program, overall SARS-COV-2 infection, SARS-COV-2 reinfection following natural infection.The analysis is done to find out the SARS- COV-2 positivity rate, SARS- COV-2 reinfection and number of days of hospitalization after the 1st dose, 2nd dose and without vaccination.

        Sample size estimation: It’s a retrospective analysis hence no formal sample size calculation is done.  

Infection after vaccination against SARS-COV-2

One-dose vaccine analysis

The probability of infection with SARS-COV-2 will be computed in individuals who have received one dose of vaccine against SARS-COV-2 starting with the first known healthcare worker recipient of vaccine in ACTREC up to the last person vaccinated prior to the data cutoff date of 18th June, 2021. The denominator for one-dose analysis will be all individuals who have received at least one dose of the vaccine prior to data cutoff date. The probability of infection after one-dose will be computed using time-to event Kaplan Meier analysis with period of risk (time point zero on ‘x’ axis) beginning with the date of 1st vaccine dose for each individual. Infection will be defined as RTPCR positivity for SARS-COV-2 at any point of time after receiving one of the vaccines and prior to receiving the 2nd dose of the vaccine, and will constitute an ‘event’ for the purpose of this analysis. For the one-dose analysis, individuals who have not experienced SARS-COV-2 infection by the date of second dose, will be censored on the date of receiving 2nd dose of the vaccine, or on the data cut-off date of June 2021 if they have not received the 2nd dose of the vaccine. The median follow-up for one-dose analysis will be the median of the time intervals from the date of 1st vaccine dose to the date of 2nd vaccine dose or the data cut-off date (in those who have not received two doses) among individuals who have not experienced an ‘event’. The readout of this analysis will be the probability of SARS-COV-2 infection-free survival after one dose of the vaccine.

Two-dose vaccine analysis

The probability of infection with SARS-COV-2 will be computed in individuals who have received two doses of the vaccine, starting with the first known healthcare worker recipient of vaccine in ACTREC up to the last person vaccinated with the second dose, prior to the data cut-off date of 18th June, 2021. The denominator for the two-dose analysis will be all individuals who have received two doses of the vaccine, prior to data cut-off date. The probability of infection after two-doses will be computed using time-to-event Kaplan Meier analysis with period of risk (time point zero on ‘x’ axis) beginning with the date of second vaccine dose, for each individual. Infection will be defined as RT-PCR positivity for SARS-COV-2 at any point of time after receiving the second dose of the vaccine and will constitute an ‘event’ for the purpose of this analysis. Individuals who are not known to have experienced documented SARSCOV-2 infection after receiving two doses of the vaccine will be censored on the date of last follow-up or the data cutoff date of 18th June 2021, whichever is earlier. The median follow-up for two-dose analysis will be the median of the time intervals from the date of 2nd vaccine dose to the date of last follow-up or the data cutoff date, whichever is earlier, among individuals who have not experienced an ‘event’. The readout of this analysis will be the probability of SARS-COV-2 infection-free survival after two doses of the vaccine.

Reinfection after prior infection with SARS-CoV-2

The probability of reinfection with SARS-COV-2 will be computed in individuals who have been known to be infected (RT-PCR for SARS-COV-2 positive) with this virus on one occasion, starting with the first known infection among ACTREC healthcare workers up to the last person infected prior to the data cut off date of 18th June, 2021. This number will constitute the denominator for this analysis. The probability of reinfection will be computed using time-to-event Kaplan Meier analysis with period of risk (time point zero on ‘x’ axis) beginning with the date of 1stinfection for each individual. Reinfection will be defined as RT-PCR positivity for SARS-COV-2 at least 8 weeks from the date of known RT-PCR negativity after 1stinfection or, if RT-PCR negativity after prior infection is not documented, at least 8 weeks from the date of rejoining work. Individuals who experience re-infection with SARS-COV-2 up to the data cutoff date will be considered to have experienced an ‘event’ for the purpose of this analysis while individuals who are not known to have experienced documented SARS-COV-2 reinfection will be censored on the data cutoff date. Individuals who experience death after 1stinfection of SARS-COV-2 will be censored on the date of death. The median follow-up for this analysis will be the median of time intervals from the date of 1stinfection to the date of last follow-up of each individual, or data cutoff date, whichever is earlier, in individuals who have not experienced an ‘event’. The readout of this analysis will be the probability of SARS-COV-2 reinfection-free survival. We acknowledge that receipt of vaccine will add another dimensions to the analysis of reinfection after prior infection. However cases of reinfection who have also received vaccine to prior the reinfection will not be excluded from the reinfection analysis, and such cases will be descriptively reported as a subset of reinfection cases.