Vaccines Reduce Transmission

Lawrence Robinson
5 min readSep 28, 2021


Example of a vaccine vial

A short article this time around, as there’s quite a lot of scientific evidence that’s been articulated here. Too many people falsely believe that Covid-19 related vaccines do not prevent transmission, in this article I address that claim with scientific evidence from studies and papers.

➡ Vaccine history
Vaccines help you to fight off microorganisms, polio reached herd immunity, smallpox reached herd immunity. The W.H.O. on 8th May 1980 said it had been eradicated, thanks to the live attenuated vaccine using the vaccinia virus against smallpox.

In 1988 cases of poliomyelitis (polio) were reduced by 75% since the vaccination campaign was launched, only 8254 cases were reported in 1994. Again vaccines help train the immune system to fight off these pathogens if they ever were to encounter them again, i.e. no host cells to infect, it eventually dies off, that’s what happened with smallpox. (Source: Alan J. Cann 1997, Principles of Molecular Virology: Second Edition, Chapter 6, Infection; p. 189)

➡ Medical definition of a vaccine
The definition of a vaccine has never changed and in layman’s terms, a vaccine is an immune system trainer that is designed to stimulate the immune system to fight off microorganisms. (Source:

➡ The scientific evidence
Vaccines, in general, prevent/mitigate transmission, the Covid-19 related ones surely do. The results from Krause et al. showed that vaccines had efficacy in preventing infection of 90% 14 days after the second dose and 80% 14 days after the first dose (Source:

In another study on vaccinated persons, the viral load was 2–4 times lower than in unvaccinated persons (Source:

One study from March with 9,109 healthcare workers in Israel found infections cut by 75 per cent after two doses of the Pfizer-BioNTech vaccine. (Source:

The New England Journal of Medicine published research letters showing reduced infections in fully vaccinated healthcare workers at the University of Texas Southwestern Medical Center, the Hadassah Hebrew University Medical Center in Jerusalem, and the University of California in Los Angeles and San Diego. (Sources: At one medical centre:
Among healthcare workers:
Among healthcare workers in California:

An early April CDC study of 3,950 healthcare workers who were tested weekly for three months after receiving both doses of either mRNA vaccine. Full vaccination reduced infection regardless of symptoms by 90 per cent, and a single dose reduced infection by 80 per cent. (Source:

Quote from one pre-print study done in the UK — “Our study demonstrates that the BNT162b2 vaccine effectively prevents both symptomatic and asymptomatic infection in working-age adults; this cohort was vaccinated when the dominant variant in circulation was B1.1.7 and demonstrates effectiveness against this variant.” (Source:

➡ Viral load decrease
I have touched in brief above about the decrease in viral load as a major factor in the decrease of viral transmission of this virus. Viral load in vaccinated individuals decrease by 1.6–20 times lower than the viral load present in infected and unvaccinated subjects (Source: (Full-text link:

➡ Delta Variant and Transmission
We all know from scientific data that the Delta variant is more potent than other variants so far, there is quite a lot of evidence that the vaccines help reduce transmission of this variant.

A recent study based in the UK which was posted to The Lancet journal found that whilst researching breakthrough cases (someone who tests positive for Covid-19 whilst being fully vaccinated), there were two case groups, one for participants who had received one dose and developed an infection 14 days later and a second group for fully vaccinated persons who also became infected seven days later. These two case groups were matched with two vaccinated control groups who did not experience breakthrough infections. The results were as follows: “Between Dec 8, 2020, and July 4, 2021, 1,240,009 COVID Symptom Study app users reported a first vaccine dose, of whom 6,030 (0·5%) subsequently tested positive for SARS-CoV-2 (cases 1), and 971,504 reported a second dose, of whom 2,370 (0·2%) subsequently tested positive for SARS-CoV-2 (cases 2).” (Source:

UK based studies from the University of Oxford looked at the following; Impact of Delta of viral burden and vaccine effectiveness, monitoring populations at increased risk for SARS-CoV-2 infection in the community and symptoms and SARS-CoV-2 positivity in the general population in the UK, these new studies are pre-print at this moment (not peer-reviewed, but interesting information nonetheless). (Source:

Yes I know what you could be thinking reader “60% of hospitalized COVID-19 patients were fully vaccinated” but this isn’t the gotcha moment you think it is, why well I’ll let you know now, you’re not looking at the maths hard enough, the first caveat is almost 80% of Israel’s population is vaccinated when comparing the vaccinated group to the unvaccinated, you see a dramatically lower rate of severe disease in the former with 5.3 vs. 16.4 cases per 100,000 people. When you factor in age as well you get a better clearer picture via data. Jeffery Morris, Director of Biostatistics at the Perelman School of Medicine at the University of Pennsylvania has a fantastic article explaining this. Well, I hope that covers the maths and data on the Israel side of things. (Source:

The short version of the math if you don’t wish to read his full article: Vaccine efficacy vs. severe disease for younger (<50yr) = 1–0.3/3.9 = 91.8% Vaccine efficacy vs. severe disease for older (>50yr) = 1- 13.6/90.9 = 85.2% These efficacies are quite high and suggest the vaccines are doing a very good job of preventing severe disease in both older and young cohorts. These levels of efficacy are much higher than the 67.5% efficacy estimate we get if the analysis is not stratified by age.”

➡ Conclusion
As you can see from the evidence-based information above, these vaccines DO reduce/mitigate infection, the Israel data is not that gotcha moment the AVs thought it would be. Thanks for reading, Lawrence. Please consider a small contribution, in the form of a beer as all articles are created in my small amount of spare time:



Lawrence Robinson

Passionate about evidence-based scientific information and tackling falsehoods that thrive on social media.