One dose of COVID vaccine halves transmission, study shows

A single dose of the coronavirus vaccines deployed in England can cut transmission of COVID-19 within households by up to 50 percent, data from a new study showed on Wednesday.

The Public Health England (PHE) research found that those who became infected three weeks after receiving their first jab of the Pfizer-BioNTech or AstraZeneca vaccines were between 38 and 49 percent less likely to pass the virus on to their household contacts compared to others who were unvaccinated.

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

The findings offer fresh insight on one of the big unknowns surrounding COVID-19 vaccinations – the extent to which they prevent transmission of the virus – and could strengthen the case for British Prime Minister Boris Johnson’s plan to remove all of England’s lockdown restrictions by mid-June.

UK Health Secretary Matt Hancock was quick to praise the results and urged people to continue coming forward for vaccines when offered a shot by health authorities.

“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,” Hancock said in a statement.

“It further reinforces that vaccines are the best way out of this pandemic as they protect you and they may prevent you from unknowingly infecting someone in your household,” he added.

‘Very promising’

The PHE study included over 57,000 contacts from 24,000 households in which there was a lab-confirmed case of COVID-19 that had received a vaccination, compared with nearly one million contacts of unvaccinated cases.

Mary Ramsay, head of immunisation at PHE, described its findings as “very encouraging” but also called on individuals who had been vaccinated to continue to act with caution in order to limit transmission.

“Even if you have been vaccinated, it is really important that you continue to act like you have the virus, practise good hand hygiene and follow social distancing guidance,” she said in a statement.

Naomi Forrester-Soto, a virologist at UK’s Keele University, also welcomed the data gathered by PHE as “very promising”.

“We had not been certain that vaccines would be able to reduce transmission at all, so the fact that this now seems to be working with just a single dose of either the Pfizer-BioNTech or AstraZeneca vaccine is really good news,” Forrester-Soto told Al Jazeera.

She added the study could be a key development in “helping people understand that by getting the vaccine they’re also protecting those people who they care about”.

The UK has one of the fastest COVID-19 vaccine rollouts in the world. Nearly 34 million adults have received a first dose of vaccine to date and a quarter of all adults have been fully inoculated.

The rapid immunisation effort has quickly generated real-world data on how the Pfizer and AstraZeneca shots work outside of clinical trials, and earlier this month PHE said the rollout had prevented more than 10,000 deaths of people aged 60 and above by the end of March.