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 1^st 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 2^nd 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 2^nd dose of the vaccine, or on the data cut-off date of June 2021 if they have not received the 2^nd dose of the vaccine. The median follow-up for one-dose analysis will be the median of the time intervals from the date of 1^st vaccine dose to the date of 2^nd 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 1^stinfection 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 1^stinfection 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 1^stinfection 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 1^stinfection 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.