Do COVID-19 Vaccines Reduce Transmission Times? A Closer Look

Aditi Bhargava
7 min readJan 11, 2022

A letter to the Editor published in the December 23rd, 2021 issue of the New England Journal of Medicine, titled “Viral Dynamics of SARS-CoV-2 Variants in Vaccinated and Unvaccinated Persons” led many media outlets to write articles with sensational headlines that COVID-19 vaccines reduce transmission in breakthrough cases. USA today headline read: “NBA study finds vaccinated people with breakthrough coronavirus infections less likely to infect others”. That is such an oxymoron! Viral infection is being transmitted from one vaccinated individual to another, and yet it is a case of glass half-full and that vaccines are effective in reducing transmission!

Now let’s examine the data presented in this NEJM letter with my reviewer hat on and examine whether the data justifies the conclusions.

The authors investigate two hypotheses: First, when an individual gets infected with the delta variant, is the viral load is higher than in those people infected with other variants of SARS-CoV-2? Second, vaccinated people when infected with SARS-CoV-2 may clear the infection more quickly than unvaccinated people.

To test their hypotheses, the authors obtained 19,941 SARS-CoV-2 viral samples from 173 individuals enrolled in the occupational health program of the National Basketball Association (NBA) between November 28, 2020, and August 11, 2021. This longitudinal set of data was analyzed prospectively.

Let’s look at the information provided for the dataset they used. They had access to a total of 19,941 longitudinal samples from 173 individuals, but viral variant information is provided from a total of 113 individuals and the fate of 19,941 samples is unclear as to how was that information utilized.

· B.1.1.7 (alpha) variant = 36 infected participants

· B.1.617.2 (delta) variant = 36 infected participants

· Variants not of current interest or concern = 41 infected participants

· Total number of individuals with information about variants = 113

· Total of vaccinated individual N = 37 vaccinated

· Total of unvaccinated individuals N = 136

Using the above datasets from 37 vaccinated and 136 unvaccinated individuals, the authors found that:

1) The peak viral load for alpha, delta, and other variants did not differ, as ascertained…



Aditi Bhargava

Dr. Aditi Bhargava is a molecular neuroendocrinologist with research focus on sex differences in stress biology and immunology.