British study finds COVID-vaccinated people, youth, less infectious for virus including Delta variant

A preprint of a study funded by the British government that has not yet been subjected to peer review appears to conclude that adults vaccinated for COVID-19 “are less infectious” and therefore do not spread it as easily as unvaccinated people, including the Delta variant.

In addition, according to Alasdair Munro, a researcher at University Hospital Southampton who posted about the study on Twitter, kids also do not appear to be spreading the original strain of the virus or the variant.

“The study we’ve all been waiting for,” he wrote in a Twitter thread. “Using data from >50,000 #COVID19 contacts, vaccinated people are less infectious EVEN with Delta, and EVEN if CT count is the same. Also, kids appear less infectious and less susceptible, including with Delta.”

“The effects of vaccination on reducing infectiousness are strongest earlier on and wane slightly with time,” he continued. “Somewhat less effective for Delta than Alpha. Effects on reducing susceptibility to infection appear stronger and remain quite well preserved, with some waning.”

“Data also clearly shows an age dependent effect,” he wrote, noting that there are “much lower rates of secondary infection from child index cases” as well as lower “secondary infection in child contacts.”

“This remains true across settings including education, except ‘Events/activities’ (?nature of contact),” he added.

According to the researchers, whose study was funded by the UK’s Department of Health and Social Care: “Vaccination reduces transmission of Delta, but by less than the Alpha variant. The impact of vaccination decreased over time. Factors other than PCR-measured viral load are important in vaccine-associated transmission reductions. Booster vaccinations may help control transmission together with preventing infections.”

In his thread, Munro suggested there could be some missing data but went on to say that wasn’t “likely.”

“It is possible cases were missed – however this is unlikely to effect the proportions significantly as the denominator is those ‘tested’ not those ‘exposed,'” he noted.

“We can finally put to bed the myth that vaccinated people are just as infectious as unvaccinated infected with Delta. Also good evidence of children being less infectious and less susceptible. Great study with very important results,” Munro concluded.

It’s unclear when the study will get its peer review, but if additional analysis bears the research out, it could have a major impact on public health policy regarding COVID moving forward.

That said, the Biden administration continues to push Americans to become vaccinated and has warned that the Delta variant remains a serious public health threat, though vaccinations can help reduce infections.

“So we’re looking not, I believe, to lockdown, but we’re looking to some pain and suffering in the future because we’re seeing the cases go up, which is the reason why we keep saying over and over again: The solution to this is get vaccinated and this would not be happening,” Dr. Anthony Fauci, the country’s lead immunologist, said in a late July interview.

But in a mid-August interview, he said mandate masks for schoolchildren as they prepared to start a new academic year remained necessary as a “mitigation” measure.

“You have to get the overwhelming proportion of people vaccinated, but you also have to do mitigation, and that gets to the controversial issue of mask-wearing, and the mandating of things. Mandating vaccines, for example, for teachers and … personnel in the school,” he said.

“We’ve got to do mitigation. Put aside all of these issues of concern about liberties and personal liberties and realize we have a common enemy and that common enemy is the virus,” he added.

Dr. Rochelle Walensky, head of the Centers for Disease Control and Prevention, went further, suggesting that transmission of the Delta variant was still highly possible even among the vaccinated.

“High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with Delta can transmit the virus,” she said.

Missy Halsey


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