Some Vaccines May Not Stop Transmission

There have recently been three supposedly safe and effective vaccines against the COVID-19 pandemic virus- Pfitzer, Moderna, and AstraZeneca . It is unknown whether the Pfitzer or Moderna vaccines can cause asymptomatic carriers. These COVID vaccines have only been proven to prevent illness, not transmission. A vaccinated person may still be able to get infected and spread the virus without showing any symptoms. This is a problem for herd immunity. These vaccines may not protect unvaccinated people from getting the virus. 


The AstraZeneca vaccine has shown that it, unlike the vaccines from Pfizer and Moderna, can stop the spread of the virus. A test conducted at Oxford showed that the vaccine can reduce transmission from asymptomatic carriers. People in the UK trial tested themselves regularly for infection from the virus, and there was a difference in the spread of the virus between the placebo and vaccinated group.

Herd Immunity

Typically, vaccines protect from both illness and transmission. This is how we achieve herd immunity. Only a certain percentage of the population must be vaccinated before the disease is unable to spread. The percentage of vaccinated people required to achieve herd immunity varies according to the disease and how easily transmissible the disease is. COVID has a case reproductive number has been estimated to fall between 2.39 and 3.44. This means that, on average, COVID has the ability to spread from an infected person to 2.39 to 3.44 other people. COVID has a much lower reproductive number than measles, which is 14-18. This means that COVID has a potentially lower bar for herd immunity than measles. It has been debated whether the herd immunity for COVID would be 60-70% or even up to 90%. Fauci has gradually nudged the percentage up from 60% to just under 90%. He based the numbers on the percentage of American surveyed who said they were willing to receive the vaccine. It is unknown how many people would need to be immune to achieve herd immunity.

Why is the COVID Vaccine Different?

The COVID vaccine is a new type of medicine. It uses bits of genetic material called messenger RNA, specifically a sequence of codes for a spike protein in the coronavirus. That particular protein in the SARS-CoV-2 virus helps it attack people’s cells. The mRNA, enfolded in bubbles of fat teaches the human immune system to fight the virus instead of allowing it to spread in both the Pfizer and Moderna vaccines.

AstraZeneca is different in that it places the spike protein in an adenovirus that usually infects chimpanzees, modified so that it cannot replicate anymore. Having a “dead” virus is the typical for a vaccine. This teaches the body to stop transmission.


The Pfizer vaccine has a success rate of 94.1% according to a New England study. The Moderna vaccine has a success rate of 95% according to the CDC. AstraZeneca, on the other hand, has a much lower efficacy. It is estimated to have a success rate between 59 and 86%. Studies on the vaccine show conflicting evidence. It is unclear whether or not the FDA will approve of the AstraZeneca vaccine due to its low efficacy. However, the current discrepancy between US supply and demand may push the FDA to approve the vaccine.

Vaccines Approved of by the FDA

The FDA has only approved of the Pfizer and Moderna vaccines under Emergency Use Authorization. Jassen and Novavax are still in phase 3. AstraZeneca may or may not be approved. An Emergency Use Authorization (EUA) is a mechanism to facilitate the availability and use of medical countermeasures, including vaccines, during public health emergencies, such as the current COVID-19 pandemic. Taking into consideration input from the FDA, manufacturers decide whether and when to submit an EUA request to FDA.

Once submitted, FDA will evaluate an EUA request and determine whether the relevant statutory criteria are met, taking into account the totality of the scientific evidence about the vaccine that is available to FDA.

The FDA sees the approved vaccines as “rigorously tested” and generally safe after being tested by tens of thousands of study participants with a two month follow-up.

Current Situation

Since vaccine distribution began in the U.S. on Dec. 14, more than 57 million doses have been administered, reaching 12.4% of the total U.S. population, according to federal data collected by the Centers for Disease Control and Prevention. The U.S. is currently administering over 1.8 million shots a day. The addition of other vaccines to the lineup could increase vaccination rates.

Big Picture

The current COVID vaccines may not protect against transmission, so it might be advisable to socially distance unless you have had the vaccine yourself. The AstraZeneca vaccine does not have great treatment rates but is proven to stop transmission. Fauci plays to the public ear, himself not knowing what the actual percentage is to get herd immunity. The FDA considers the currently approved vaccines to be safe. So far, millions of people have received the vaccine, but there is still a long way to go.

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