Household transmission reduced after first vaccine shot

A new study by Public Health England, which has not been peer-reviewed yet, indicates that people who have received one dose of the Pfizer-BioNTech or Oxford-AstraZeneca vaccine are 40–50% less likely to pass on the SARS-CoV-2 virus if they contract it.

The researchers looked at data from 365,447 households in which one person had a COVID-19 diagnosis. For each of these index cases, the team looked at whether anyone else in the household also had a positive COVID-19 test result 2 to 14 days later. In total, they found 102,662 such secondary cases.

They then examined whether there was a difference in the rate of secondary cases in households where the index case had received one shot of the Pfizer-BioNTech or Oxford-AstraZeneca vaccine.

Starting at 14 days after vaccination, the likelihood of passing on the virus to a household member dropped significantly. These results show that the likelihood of household transmission is 40–50% lower for households in which the index cases are vaccinated 21 days or more prior to testing positive (compared [with] no vaccination), with similar effects for both the [Oxford-AstraZeneca] and [Pfizer-BioNTech] vaccines,” the authors of the report conclude.

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