Vaccines Cut Household COVID-19 Transmission by Up to a Half, English Data Shows

LONDON (Reuters) – COVID-19 vaccines deployed in England can cut transmission of the coronavirus in households by up to a half, data from Public Health England (PHE) showed on Wednesday, in addition to the protection the shots offer against symptomatic infection.

The research offers insight on one of the big unknowns over COVID-19 vaccinations – the extent to which they prevent transmission of the coronavirus – and could strengthen the case for Prime Minister Boris Johnson’s plans to end England’s lockdown in June.

“We already know vaccines save lives and this study is the most comprehensive real-world data showing they also cut transmission of this deadly virus,” health minister Matt Hancock said.

New research showed that people who became infected with the coronavirus three weeks after receiving one dose of Pfizer or AstraZeneca vaccine were between 38% to 49% less likely to pass it on to household contacts compared to those who were unvaccinated.

The shots also stop a vaccinated person developing symptomatic infection to start with, reducing the risk by around 60% to 65% from four weeks after one dose of either vaccine.

“While these findings are very encouraging, even if you have been vaccinated, it is really important that you continue to act like you have the virus,” said Mary Ramsay, head of immunisation at PHE.

The study included over 57,000 contacts from 24,000 households in which there was a lab-confirmed case that had received a vaccination, PHE said, compared with nearly 1 million contacts of unvaccinated cases.

The analysis, published as a preprint on the Knowledge Hub website, found there were 196 secondary cases in 3,424 contacts (5.72%) where the index case received the ChAdOx1 nCoV-19 vaccine 21 days or more before testing positive, and 371 secondary cases in 5,939 contacts (6.25%) where the index case received the BNT162b2 vaccine 21 days or more before testing positive. The unadjusted odds ratio for being a secondary case if the index case was vaccinated with ChAdOx1 nCoV-19 (vs. index case not vaccinated) was 0.55, and for BNT162b2, 0.57.

Britain has one of the fastest COVID-19 vaccine rollouts in the world, with over 33.8 million first doses given and a quarter of adults receiving both shots.

That has generated real-world data on how Pfizer and AstraZeneca work outside the setting of clinical trials, and earlier this month PHE said the rollout had prevented over 10,000 deaths of people aged 60 and older by the end of March.

SOURCE: Public Health England, online April 28, 2021.

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