The COVID-19 vaccine does not prevent people from spreading the delta variant to unvaccinated members of their household.
A study published in The Lancet Infectious Diseases medical journal on Oct. 28 reported the results of a year-long study conducted in the United Kingdom. It documented the health of 621 people with mild COVID cases and found that the vaccination did not significantly change the viral load, which was similar regardless of vaccination status.
The researchers found that 25% of vaccinated household contacts still contracted the disease from an index case, while 38% of those who hadn’t had shots became infected.
By comparison, vaccination did reduce household transmission of the alpha variant by between 40% and 50%.
“Our findings show that vaccination alone is not enough to prevent people from being infected with the delta variant and spreading it in household settings,” said Ajit Lalvani, a professor of infectious diseases at Imperial College London who co-led the study. “The ongoing transmission we are seeing between vaccinated people makes it essential for unvaccinated people to get vaccinated to protect themselves.”
The researchers wrote that vaccination and non-pharmacological interventions would be a priority in slowing the delta variant’s spread. Additionally, they encouraged the vaccination of teenagers and booster programs “to increase the currently limited effect of vaccination on transmission.”
“The results go some way toward explaining why the delta variant is so infectious even in nations with successful vaccine rollouts, and why the unvaccinated can’t assume they are protected because others have had shots,” reports Bloomberg. “Those who were inoculated cleared the virus more quickly and had milder cases, while unvaccinated household members were more likely to suffer from severe disease and hospitalization.”
The delta variant is believed to be the most common coronavirus strain worldwide. It was first documented in India at the end of 2020. Today, it is most prevalent in the United State (707,663 cases) and the United Kingdom (658,881 cases).