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Lancet Study: COVID-19 Transmission Rates Similar Between Vaccinated and Unvaccinated

Steven Li, MD
Steven Li is a medical professional with a passion for lifelong learning and spreading truth to the world. He specializes in the fields of health and science.
Published: November 6, 2021
A study in The Lancet showed transmission of COVID-19 was similar between the vaccinated and unvaccinated
Commuters ride a Transport for London (TfL) underground train in London on October 20, 2021. UK researchers used a contact tracing study to discover that COVID-19 vaccines are doing little to inhibit the spread of the disease. (Image: TOLGA AKMEN/AFP via Getty Images)

According to a recent study published in The Lancet on Oct. 29 by authors in the UK and funded by the National Institute for Health Research (NIHR), while vaccination for Coronavirus Disease 2019 (COVID-19) may reduce the rates of hospital admissions and deaths, “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.”

The paper continues, “Vaccine effectiveness against infection is reduced for delta. Determining the extent of transmission from vaccinated delta-infected individuals to their vaccinated contacts is a public health priority.” Furthermore, “Vaccine effectiveness against infection is reduced for delta, compared with alpha, and the delta variant continues to cause a high burden of cases even in countries with high vaccination coverage.”

Indeed, the findings from the study call into question the degree of public health benefit provided by vaccination and the scientific basis for vaccine mandates.

Vaccines do not significantly affect household transmission

The authors investigated the “community transmission and viral load kinetics” of the Delta variant through a prospective, longitudinal, cohort study. Data was taken from 602 community contacts of 471 COVID-19 index cases between Sept 13, 2020 and Sept. 15, 2021.

Index contacts and their contacts were followed in the community soon after exposure to the Delta variant of the SARS-CoV-2 virus, and daily quantitative RT-PCR tests were conducted on samples from the upper respiratory tracts of the subjects for 14 to 20 days. Individuals were classified as “fully vaccinated if they had received two doses of a COVID-19 vaccine at least 7 days before study enrolment.”

The primary objectives of the study were to evaluate the secondary attack rate (SAR) in household contacts based on vaccination status, and to also analyze viral load kinetics via “differences in the peak viral load, viral growth rate, and viral decline rate.”

The results showed that SAR for household contacts was “not significantly higher in unvaccinated (38%, 95% CI 24–53) than fully vaccinated (25%, 18–33) household contacts.”

In fact, the data showed that fully vaccinated contacts were infected by fully vaccinated individuals (38.7%, 12 of 31) at a higher rate than by unvaccinated individuals (23.5%, 12 of 51), although the statistical significance of this difference was not commented on.

The study additionally stated, “The SAR in household contacts exposed to fully vaccinated index cases was 25% (95% CI 15–35; 17 of 69), which is similar to the SAR in household contacts exposed to unvaccinated index cases (23% [15–31]; 23 of 100.” In other words, “The proportion of infected contacts was similar regardless of the index cases’ vaccination status [emphasis added],” which “indicates that breakthrough infections in fully vaccinated people can efficiently transmit infection in the household setting.”

The 163 PCR-positive individuals were 55 percent female, 82 percent White, and had a median age of 36-years-old. Researchers note, “The proportion of asymptomatic cases did not differ among fully vaccinated, partially vaccinated, and unvaccinated delta groups.” Also, while “peak viral load did not differ by variant or vaccination status,” the “peak viral load increases with age.”

Evidence of waning immunity was observed, as “the time interval between vaccination and study recruitment was significantly higher in fully vaccinated PCR-positive contacts than fully vaccinated PCR-negative contacts, suggesting that susceptibility to infection increases with time as soon as 2–3 months after vaccination—consistent with waning protective immunity.”

The authors conclude, “Our findings help to explain how and why the delta variant is being transmitted so effectively in populations with high vaccine coverage. Although current vaccines remain effective at preventing severe disease and deaths from COVID-19, our findings suggest that vaccination alone is not sufficient to prevent all transmission of the delta variant in the household setting, where exposure is close and prolonged.”