Do the mRNA Vaccines Reduce or Prevent Transmission?

I struggle to understand the messaging around the vaccines and what they are purported to do, and how mask mandates seem contrary to a vaccine mandate, especially when it results in firing healthcare workers.

First, I think it will be helpful to understand my current conclusion as I will likely, unintentionally, view the following studies and sources with this bias. Knowing my bias, I hope people can elucidate me in places where I may be misunderstanding or misrepresenting the data.

My current conclusion is that the mRNA vaccines are effective at reducing transmission, and hospitalization (aka severe-illness), in the short term. I have not seen any evidence they reduce death, and it seems that both reduction in transmission and hospitalization wanes somewhere in the 3-9 month range, with reduction of transmission waning sooner than hospitalization.

What Does the CDC Say?

As the CDC is a Public Health Organization (PHO) where it's decisions carry weight across other PHOs, I think it's a good place to start.

Effectiveness of COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Frontline Workers Before and During B.1.617.2 (Delta) Variant Predominance — Eight U.S. Locations, December 2020–August 2021

This study confirms that between December 14, 2020–April 10, 2021, the vaccines were "approximately 90% effective in preventing symptomatic and asymptomatic infection with SARS-CoV-2." That is a five-month period. From April 10-August 14, Vaccine Efficacy (VE) declined to 66% which was the period in which the Delta variant became dominant. But, they conclude "VE might also be declining as time since vaccination increases and because of poor precision in estimates due to limited number of weeks of observation and few infections among participants."

So, efficacy wanes after 5 months, and we aren't too sure why--it could be time since vaccination, Delta, or perhaps both. I'd also say, as this study looks at around ~5000 frontline workers in 6 different healthcare locations, it may not be fully representive.

Even more interesting, is this study was published by the CDC on August 24, 2021, even though CDC Director Rochelle Walensky in an interview with CNN, can be seen saying "[the vaccines] continue to work well with delta with regard to severe illness and death, but what they can't do anymore is prevent transmission." This was said on August 6th, 2021. So, the vaccines "work well" but don't prevent transmission?

Did the Vaccines Ever Prevent Transmission?

Well, back in December 2020, Dr. Larry Corey of the University of Washington who is a Professor of the Department of Laboratory Medicine & Pathology, and member of the Division of Vaccine & Infectious Disease (VIDD), didn't think so.

Current phase 3 trials tell us whether COVID-19 vaccines prevent illness and hospitalization, but not whether the vaccines prevent infection and transmission. Additional studies will need to be done, perhaps within households and on college campuses, to see whether COVID-19 vaccines prevent virus transmission, allowing us to return to a more normal life.

If we look at the Pfizer and BioNTech FDA Briefing Document from December 10, 2020, we can see "Data are limited to assess the effect of the vaccine against transmission of SARS-CoV-2 from individuals who are infected despite vaccination."

I'd argue that the data Pfizer and BioNTech provide to the FDA to get Emergency Use Authorization can be considered good primary data. And this primary data does not indicate a reduction in transmission. So, none of the early trials that lead to the vaccines getting authorized looked at transmission. Why then, did our public health officials tell us that getting the vaccine would protect our community? That it would protect the vulnerable and immunocomprimised?

But There Must Be Studies Suggesting a Reduction in Transmission, No?

Indeed, there are more recent studies. One pre-print from the Dutch Ministry of Health (meaning the study has not been peer-reviewed or published by a Journal yet), claims "Our results indicate that vaccination confers protection against onward transmission from vaccinated index cases, albeit somewhat less for Delta than for Alpha." But comes with the caveat, "Possible waning of vaccine effectiveness against infection and against onward transmission could result in increases in SARS-CoV-2 circulation among populations with high vaccine coverage."

[Update Nov 18, 2021] I found another recent study on transmission by scouring Google Scholar, Effect of Vaccination on Transmission of SARS-CoV-2. The aim of the study was to look at the effect of vaccination of health care workers and the risk of COVID-19 among their household members. Outcomes were determined by "any confirmed case of Covid-19 that occurred between December 8, 2020, and March 3, 2021". So, 85 days, which is not a very long period. The supplementary appendix indicates the health care cohort only includes 18-65 year olds, while the household cohort includes all ages, which they acknowledge: "We are therefore unable to evaluate the impact on vaccinating elderly or vulnerable individuals." Anyway, the study concludes (emphasis mine):

Given that vaccination reduces asymptomatic infection with SARS-CoV-2, it is plausible that vaccination reduces transmission; however, data from clinical trials and observational studies are lacking. We provide empirical evidence suggesting that vaccination may reduce transmission by showing that vaccination of health care workers is associated with a decrease in documented cases of Covid-19 among members of their households. This finding is reassuring for health care workers and their families.

So, in a period of 85 days, or less than 3 months, there may be a reduction of transmission in the vaccinated. One, this isn't very compelling evidence. Two, this was published on Oct 28, 2021, meaning it could not have informed public health policy.

Another study recently published in The Lancet concludes "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." More than that, a prominent pro-vaccine figurehead, Bill Gates recently said "we didn't have vaccines that block transmission.." I don't know why he uses the past-tense, but intereresting nonetheless.

But, what does it all mean Basil?!

Well, it seems like transmission was never prevented nor significantly reduced. Which, to me, means we can leave out transmission as a characteristic of determining if the vaccines make sense or not for different people. Further, since these mRNA vaccines don't prevent transmission, the vulnerable and immunocomprimised are not protected by those who opt to get the vaccine. Which is why public health officials are mandating mask wearing, as we try to actually reduce transmission.

But, why mandate the vaccine? Or, more specifically, why do our Provincial and Federal mandates only push the vaccine rather than the more sensical covid passports of European countries? Since transmission is not reduced by the vaccine, should we not be opting for negative test results? Especially rapid-antigen tests? As well as counting natural immunity? It seems pretty clear, that relying solely on vaccination status is not enough to stop transmission.

This is very confusing, especially at a time when social media sites are banning accounts that spread misinformation, such as YouTube which removes videos that include "claims that vaccines do not reduce transmission"...Why?! I could quote the Pfizer document to the FDA and be in violation of "misinformation guidelines"?

Where did people even get the idea that these treatments would reduce transmission when there hasn't been data to back it up? Moreover, I don't understand why our governments are limiting the tools we could use to mitigate the effects of this disease, especially to those who are most vulnerable. How does firing health care workers who remain unvaccinated make any sense, if the vaccine doesn't reduce transmission? Am I missing something?

November 13, 2021