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Study: Vaccinated as likely to spread delta variant within household as unvaccinated

The study found that while COVID-19 vaccines help protect the vaccinated from severe illness with the delta variant, it does little reduce the spread in households.

WASHINGTON — A newly-published study shows that while vaccines are still effective in reducing hospitalization or death from the delta variant of COVID-19, the vaccine offers little protection against spreading the variant within a person's own household.

The article, published Friday in the peer-reviewed journal Lancet Infectious Diseases, looked at more than 600 people in the United Kingdom over the course of a year and analyzed the viral load, or the amount of the virus in the body, of vaccinated and unvaccinated individuals. 

Researchers found that 25% of vaccinated household members exposed to the delta variant contracted COVID-19 compared to 38% of unvaccinated household members. But in terms of the source of the infection, infections from those exposed to fully vaccinated people was similar to infections from those exposed to unvaccinated people. 

The study also found that vaccinated individuals with the delta variant saw their viral load decline faster than unvaccinated people whether those people had the original strain of COVID-19, the alpha variant or the delta variant.

The Centers for Disease Control and Prevention has been telling Americans this for months: breakthrough cases happen and vaccinated people can still transmit the delta variant. The study published in the Lancet puts those claims into raw data.

"Vaccination reduces the risk of delta variant infection and accelerates viral clearance," the study concludes. "Nonetheless, fully vaccinated individuals with breakthrough infections have peak viral load similar to unvaccinated cases and can efficiently transmit infection in household settings, including to fully vaccinated contacts. Host–virus interactions early in infection may shape the entire viral trajectory."

According to the CDC, the delta variant is the most contagious COVID-19 variant, more than twice as contagious as previous variants.