University of Oxford investigators used contact tracing to conclude that vaccinated individuals are less likely to spread COVID-19 even if they become reinfected.
One of the primary tools of an infection preventionist’s (IP’s) trade helped scientists determine that people who’ve been vaccinated against COVID-19 are less likely to spread the disease even if a breakthrough infection happens to them. Investigators with the University of Oxford used contact tracing to find about 150,000 contacts from about 100,000 initial infections.
“We performed a retrospective observational cohort study of contacts of SARS-CoV-2-infected index cases using contact testing data from England,” states the study, which has not yet been peer reviewed but is available as a preprint on the server MedRxiv. “We used multivariable logistic regression to investigate the impact of index case and contact vaccination on transmission, and how this varies with Alpha and Delta variants (classified using S-gene detection/calendar trends) and time since second vaccination.”
The study adds to a growing consensus in the medical world that COVID-19 vaccines can reduce the transmission of the highly infectious Delta variant.
“Vaccination reduces transmission of Delta, but by less than the Alpha variant,” the study states.
The investigators found that 2 doses of the Pfizer/BioNTech and the Oxford AstraZeneca vaccines reduced COVID-19 positivity rates in contacts, but the contact who’d been infected by someone with the Delta variant was 65% less likely to test positive for COVID-19 if the person who’d transmitted the infection had been given the Pfizer vaccine. If the contact had been infected by someone who’d been given the AstraZeneca vaccine, that contact was 36% less likely to test positive for COVID-19.
Kevin Kavanagh, MD, a member of Infection Control Today® ‘s (ICT®’s) Editorial Advisory Board says that the study shows that boosters need to be offered to offset the waning effectiveness of vaccines. “Stopping the spread of disease is a high priority not only to prevent severe acute illness and long COVID but also to prevent viral mutations,” says Kavanagh. “Vaccines appear to be a vital strategy in lowering the R0 of SARS-CoV-2 below 1.0 and should be used in combination with surgical or N95 masks, social distancing, testing, contact tracing and improvements in building ventilation.”
Even though the findings had not yet been peer reviewed scientists not associated with the study praised it.
Aaron Richterman, MD, MPH, an infectious disease physician at the University of Pennsylvania, told NBC News that “it’s the highest quality study we have so far on the question of infectiousness of vaccinated people infected with Delta.”
Susan Butler-Wu, PhD, a clinical microbiologist at the University of Southern California, echoed Kavanagh when she told NBC News that “we need to combine our vaccines with other measures to reduce how much virus we get exposed to by things like masking and testing. Additive measures is the name of the game here.”