Impact of vaccination on household transmission of SARS-COV-2 in England
Conclusions " In addition to the direct effects of preventing cases and reducing severity, we have shown that both the ChAdOx1 nCoV-19 and BNT162b2 vaccines are associated with reduced likelihood of household transmission by 40-50% from individuals diagnosed with COVID-19 after vaccination, highlighting important wider benefits to close contacts. . . . these results could also have implications for transmissibility in other settings with similar transmission risks."
Comment: Can't get much closer than (and so risk of catching from) another asymptomatic household member.
Dr Peter English (Retired Consultant in Communicable Disease Control, Former Editor of Vaccines in Practice Magazine, Immediate past Chair of the BMA Public Health Medicine Committee) assessment:
". . . substantial numbers, so the paper's conclusions are robust.
“We have mounting evidence of the real-world effectiveness of the Covid-19 vaccines. Vaccines are more . . . effective against death and critical care admission, and against hospital admission, than [less serious disease] and still less effective against asymptomatic disease [infect
ed]. . . . their efficacy in terms of preventing people from being infect
ious is harder to evaluate – that is where this study comes in.
“The [paper] may, . . . have underestimated the effectiveness of the vaccines in preventing transmission, as their definition of secondary cases is likely to have included some co-cases (people who acquired their infection from the same source as the “index case”, rather than from the index case).
“These findings are really important [and] extremely encouraging. They add to our reasons to hope that the vaccines will truly add to herd immunity. . . . This study shows that even if people who are vaccinated do become infected, they are considerably less likely to be infectious, and to pass the infection on to others."
Comment: The more effective the vaccination regime is at preventing transmission the quicker herd immunity will be reached (though it may still never be reached if the required percentage of the population cannot be vaccinated (low take up and 13M under 16s).