Not in the News: COVID Epidemiology
It is negligent to ignore the vaccinated as a source of transmission when deciding about public health control measures.
An article in Lancet Regional Health EU titled: “The epidemiological relevance of the COVID-19-vaccinated population is increasing” has important aggregated data on the significance of the vaccinated as sources for transmission of SARS-CoV-2 (1).
The article highlights that high COVID-19 vaccination rates have not reduced transmission of SARS-CoV-2 in populations by reducing the number of possible sources for transmission and thereby reduced the burden of COVID-19 disease. Recent data indicates that the epidemiological relevance of COVID-19 vaccinated individuals as a source of transmission is increasing, as there are fewer unvaccinated and more people are naturally immune.
Another paper out of the UK shows that fully vaccinated individuals with breakthrough infections have peak viral loads similar to the unvaccinated, and that fully vaccinated individuals can efficiently transmit infection in household settings. The authors conclude that host–virus interactions early in infection may shape the entire viral trajectory. In this study, the secondary attack rates among household contacts exposed to fully vaccinated index cases was similar to household contacts exposed to unvaccinated index cases (25% for vaccinated vs 23% for unvaccinated). 12 of 31 infections in fully vaccinated household contacts (39%) arose from fully vaccinated epidemiologically linked index cases. Peak viral load did not differ by vaccination status or variant type (2).
In yet another report by the Robert Koch Institute, it was shown that In Germany, the rate of symptomatic COVID-19 cases among the fully vaccinated (“breakthrough infections”, reported weekly since 21, July 2021) was 16.9% at that time among patients of 60 years and older. This proportion has increased weekly and was 58.9% on October 27, 2021. This provides clear evidence of the increasing relevance of the fully vaccinated as a possible source of transmission (3).
In the UK, a similar situation shows among citizens of 60 years or older, the fully vaccinated accounted for 89.7% of the SARS-CoV-2 cases versus 3.4% among the unvaccinated (4).
A report out of Israel reports a nosocomial outbreak involving 16 healthcare workers, 23 exposed patients and two family members. The source was a fully vaccinated COVID-19 patient. The vaccination rate was 96.2% among all 248 exposed individuals (151 healthcare workers and 97 patients). Our of the 248 people, fourteen fully vaccinated patients became severely ill or died, and two unvaccinated patients developed mild disease (5).
The US Centers for Disease Control and Prevention (CDC) identifies four of the top five counties with the highest percentage of fully vaccinated population (99.9–84.3%) as “high” transmission counties (6).
The initial analysis of the Omicron variant is that it is less virulent and more transmissible. Early data also suggests that the current vaccines, developed against the Alpha strain of COVID, are no that useful in stopping transmission. Data also suggest that break-through cases of fully vaccinated individuals are going to be the norm with the Omicron variant.
The data above should make decision makers question their assumptions that the vaccinated can be excluded as a source of transmission.
“It appears to be grossly negligent to ignore the vaccinated population as a possible and relevant source of transmission when deciding about public health control measures (1).”
Community transmission and viral load kinetics of the SARS-CoV-2 delta (B.1.617.2) variant in vaccinated and unvaccinated individuals in the UK: a prospective, longitudinal, cohort study. Lancet Infect Dis. 2021.
Thank you to “Pico”, 2021 for the use of the cartoon!