Effect of vaccination on transmission of COVID-19: an observational study in healthcare workers and their households

BackgroundThe effect of vaccination for COVID-19 on onward transmission is unknown.

MethodsA national record linkage study determined documented COVID-19 cases and hospitalisations in unvaccinated household members of vaccinated and unvaccinated healthcare workers from 8th December 2020 to 3rd March 2021. The primary endpoint was COVID-19 14 days following the first dose.

ResultsThe cohort comprised of 194,362 household members (mean age 31{middle dot}1 {+/-} 20{middle dot}9 years) and 144,525 healthcare workers (mean age 44{middle dot}4 {+/-} 11{middle dot}4 years). 113,253 (78{middle dot}3%) of healthcare workers received at least one dose of the BNT162b2 mRNA or ChAdOx1 nCoV-19 vaccine and 36,227 (25{middle dot}1%) received a second dose. There were 3,123 and 4,343 documented COVID-19 cases and 175 and 177 COVID-19 hospitalisations in household members of healthcare workers and healthcare workers respectively. Household members of vaccinated healthcare workers had a lower risk of COVID-19 case compared to household members of unvaccinated healthcare worker (rate per 100 person-years 9{middle dot}40 versus 5{middle dot}93; HR 0{middle dot}70, 95% confidence interval [CI] 0{middle dot}63 to 0{middle dot}78). The effect size for COVID-19 hospitalisation was similar, with the confidence interval crossing the null (HR 0{middle dot}77 [95% CI 0{middle dot}53 to 1{middle dot}10]). The rate per 100 person years was lower in vaccinated compared to unvaccinated healthcare workers for documented (20{middle dot}13 versus 8{middle dot}51; HR 0{middle dot}45 [95% CI 0{middle dot}42 to 0{middle dot}49]) and hospitalized COVID-19 (0{middle dot}97 versus 0{middle dot}14; HR 0{middle dot}16 [95% CI 0{middle dot}09 to 0{middle dot}27]). Compared to the period before the first dose, the risk of documented COVID-19 case was lower at [≥] 14 days after the second dose for household members (HR 0{middle dot}46 [95% CI 0{middle dot}30to 0{middle dot}70]) and healthcare workers (HR 0{middle dot}08 [95% CI 0{middle dot}04 to 0{middle dot}17]).

InterpretationVaccination of health care workers was associated with a substantial reduction in COVID-19 cases in household contacts consistent with an effect of vaccination on transmission.