Single dose of vaccine can almost halve transmission

A nurse, Cindy Mendez, wearing a protective mask, holds a syringe containing a dose of Pfizer-BioNTech COVID-19 vaccine during the coronavirus disease (COVID-19) pandemic at NYC Health + Hospitals Harlem Hospital in the Manhattan neighborhood of New York City. New York, February 25, 2021.

Jeenah Moon | Reuters

LONDON – A single dose of coronavirus vaccine can cut transmission within a household by up to half, a study by Public Health England found.

People who became infected with the coronavirus three weeks after receiving a single dose of the Pfizer-BioNTech or AstraZeneca-University of Oxford vaccine were between 38% and 49% less likely to pass the virus on to their household contacts than those who weren’t vaccinated, the PHE found -Study.

Protection was observed approximately 14 days after vaccination with similar levels of protection regardless of the age of the cases or contacts.

That protection comes on top of the reduced risk that a vaccinated person will develop symptomatic infection in the first place, which is around 60% to 65% – four weeks after a dose of either vaccine, according to PHE. Both doses of a coronavirus vaccine (the delay between doses is up to 12 weeks in the UK) offer even greater protection against Covid infections.

UK Health Secretary Matt Hancock hailed the study’s results as “great news”. “We already know that vaccines save lives, and this study is the most comprehensive real-world data to show that they also reduce the transmission of this deadly virus.”

“It further underscores that vaccines are the best way out of this pandemic as they protect you and potentially prevent you from unwittingly infecting anyone in your household.”

“I urge everyone to get their vaccines as soon as they are eligible and make sure you get your second dose to ensure the best possible protection,” he added.

Both Pfizer BioNTech and AstraZeneca vaccines are used extensively in the UK, and the Moderna vaccine is now also included in the immunization program.

The introduction of vaccines was a tremendous success in the UK and a silver lining after the devastation of the pandemic that has caused over 127,000 deaths in the country to date.

In the UK, cases, hospitalizations and deaths have fallen dramatically since it was launched in December, along with strict lockdown measures. To date, nearly 34 million adults in the UK have had a first dose of vaccine and over 13 million two doses, government data shows.

The PHE study found that households are at high risk for transmission and provide early evidence of the effects of vaccines on preventing transmission. Similar results might be expected in other settings with similar transmission risks, for example in shared apartments and prisons.

The study, which is a pre-print that has not yet been peer-reviewed, included over 57,000 contacts from 24,000 households who had a laboratory-confirmed coronavirus case vaccinated, compared to nearly 1 million contacts from unvaccinated cases.

By linking case and household contact data with vaccination status, the study compared the probability of transmission for a vaccinated case with a non-vaccinated one.

PHE is also conducting separate studies on the effects of vaccination on transmission in the broader population.

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