Covid-19: One dose of vaccine cuts risk of passing on infection by as much as 50%, research shows

Adults infected with covid-19 three weeks after receiving one dose of the Pfizer-BioNTech or Oxford-AstraZeneca vaccine were 38-49% less likely to pass the virus on to their household contacts than people who were unvaccinated, a preprint released by Public Health England has shown.1

The research looked at the proportion of household contacts who tested positive 2-14 days after vaccinated index cases, comparing this with households where the index case was unvaccinated. The team said that protection was seen from around 14 days after vaccination, and similar levels were observed regardless of the age of cases or contacts.

Public Health England said that this protection was on top of the reduced risk of a vaccinated person developing symptomatic infection in the first place, which was around 60-65% four weeks after one dose of either vaccine. …