Vaccines protect people from diseases, but don’t always prevent disease transmission; research ongoing to determine if COVID-19 vaccines stop transmission

A YouTube live stream recorded on 5 January 2021, featured David Martin, who claimed that the COVID-19 RNA vaccines are not vaccines because they don’t fulfill the definitions of a vaccine according to the U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA). The original live stream, titled “Focus on Fauci” and published by New Earth Project, was viewed more than 57,000 times, with copies of the recording shared on social media platforms like Facebook (see examples here and here).

A vaccine protects a person from a particular disease, but doesn’t necessarily prevent disease transmission

By examining both the CDC and FDA’s definitions of a vaccine, it is clear that Martin’s claim is inaccurate, as neither agency stipulates that a vaccine must both provide immunity and prevent disease transmission.

The CDC defines the term “vaccine” as:

“A product that stimulates a person’s immune system to produce immunity to a specific disease, protecting the person from that disease. Vaccines are usually administered through needle injections, but can also be administered by mouth or sprayed into the nose.”

The FDA explains how vaccines work:

“Vaccines work by mimicking the infectious bacteria or viruses that cause disease. Vaccination stimulates the body’s immune system to build up defenses against the infectious bacteria or virus (organism) without causing the disease. The parts of the infectious organism that the immune system recognizes are foreign to the body and are called antigens. Vaccination exposes the body to these antigens.

Some vaccines contain weakened versions of a bacteria or virus, other vaccines contain only part of the bacteria or virus. Some vaccines contain only the genetic material for a specific protein and direct the body to produce a small amount of that protein. The body’s immune system reacts defensively once it detects this protein.

After vaccination, the immune system is prepared to respond quickly and forcefully when the body encounters the real disease-causing organism.”

In addition, Vaccines.gov, a website run by the U.S. Department of Health and Human Services, defines a vaccine thus:

“A vaccine is made from very small amounts of weak or dead germs that can cause diseases — for example, viruses, bacteria, or toxins. It prepares your body to fight the disease faster and more effectively so you won’t get sick.”

And the World Health Organization explains how vaccines work:

“Vaccination is a simple, safe, and effective way of protecting people against harmful diseases, before they come into contact with them. It uses your body’s natural defenses to build resistance to specific infections and makes your immune system stronger.

Vaccines train your immune system to create antibodies, just as it does when it’s exposed to a disease. However, because vaccines contain only killed or weakened forms of germs like viruses or bacteria, they do not cause the disease or put you at risk of its complications.”

As the above citations from the U.S. government and federal agencies, as well as the World Health Organization show, a vaccine is first and foremost a substance that helps the body generate protection from disease in the vaccinated individual. The definitions and explanations don’t stipulate that a vaccine must also prevent disease transmission, as Martin claims.

The two COVID-19 vaccines that are approved for emergency use by the FDA, one co-developed by Pfizer and BioNTech and the other by Moderna, meet the requirement for a vaccine to prevent disease. Therefore, both are vaccines according to the definitions outlined by the CDC and FDA. Preliminary data from clinical trials indicate that both vaccines have more than 94% efficacy in preventing COVID-19 in vaccinated individuals. Clinical trials are still underway, so estimates of each vaccine’s efficacy may change.

The FDA acknowledged that a vaccine may not always prevent disease transmission. In the webpage addressing frequently asked questions about the Pfizer-BioNTech vaccine, the FDA stated:

“Most vaccines that protect from viral illnesses also reduce transmission of the virus that causes the disease by those who are vaccinated. While it is hoped this will be the case, the scientific community does not yet know if the Pfizer-BioNTech COVID-19 Vaccine will reduce such transmission.”

Scientists are still gathering data to find out whether COVID-19 vaccines prevent transmission of the disease

The FDA’s statement above also refutes Martin’s claim that the vaccines don’t prevent transmission. At the moment, it is unclear whether the COVID-19 vaccines prevent transmission of the disease, but studies are being conducted to address this question.

A COVID-19 vaccine that prevents disease and stops transmission would enable a much more rapid end to the pandemic compared to a vaccine that only prevents disease in vaccinated individuals.

However, a vaccine that prevents COVID-19 but not transmission is still better than no vaccine in terms of reducing the spread of the disease. A COVID-19 vaccine that prevents disease will reduce the number of cases that require medical attention, thereby alleviating the burden on the healthcare system. It also decreases the number of deaths and complications arising from severe COVID-19 cases.

In fact, before the pandemic, scientists observed reductions in severe disease cases with other vaccines, like the rotavirus and poliovirus vaccines. Sarah Caddy, a clinical research fellow in viral immunology at the University of Cambridge, explained in this article published by The Conversation:

“Some vaccines stop you getting symptomatic disease, but others stop you getting infected too. The latter is known as ‘sterilising immunity’. With sterilising immunity, the virus can’t even gain a toehold in the body because the immune system stops the virus entering cells and replicating.

[…] In an ideal world, all vaccines would induce sterilising immunity. In reality, it is actually extremely difficult to produce vaccines that stop virus infection altogether. Most vaccines that are in routine use today do not achieve this. For example, vaccines targeting rotavirus, a common cause of diarrhoea in infants, are only capable of preventing severe disease. But this has still proven invaluable in controlling the virus. In the US, there has been almost 90% fewer cases of rotavirus-associated hospital visits since the vaccine was introduced in 2006. A similar situation occurs with the current poliovirus vaccines, yet there is hope this virus could be eradicated globally.”

In this Nature article, Florian Krammer, a professor of vaccinology at Icahn School of Medicine at Mount Sinai, stated “Right now, we need a vaccine that works,” even if the vaccine only works for a few months or doesn’t stop transmission. “That’s what we need in order to get half-way back to normal.”

That being said, scientists think it is likely the COVID-19 vaccines also reduce transmission to some degree. In this Quartz article, Matthew Woodruff, an immunologist at Emory University, said, “I can’t imagine how the vaccine would prevent symptomatic infection at the efficacies that [companies] reported and have no impact on transmission.”

However, it is unclear whether the COVID-19 vaccines completely block transmission (by preventing infection in vaccinated individuals altogether) or simply reduce the likelihood of transmission by reducing the amount of virus produced by a vaccinated person who becomes infected.

Akiko Iwasaki, an immunologist and professor at Yale School of Medicine, told the New York Times, “My feeling is that once you develop some form of immunity with the vaccine, your ability to get infected will also go down […] Even if you’re infected, the level of virus that you replicate in your nose should be reduced.”

Samuel Scarpino, director of the Emergent Epidemics Lab and assistant professor at Northeastern University, told Wired, “We don’t have any reason to think the Pfizer and Moderna vaccines won’t block transmission. It’s just not what has actually been measured, and something we aren’t likely to find out until we either start mass vaccination and/or they release more detailed information on the study locations—and epidemiologists start looking for effects of herd immunity.”

As John Moore, a virologist and professor at Weill Cornell Medicine, said to the New York Times, “The more you reduce viral load, the less likely you are to be transmissible”. But he added that “all of these are things where data trumps theory, and we need the data”.

Because we don’t know for certain if the COVID-19 vaccines reduce or stop transmission, it is important for people to continue exercising precautions and preventative measures to reduce the spread of the disease, such as maintaining good hand hygiene, wearing face masks, and practicing physical distancing.

The COVID-19 RNA vaccines cannot cause cells to manufacture the pathogen

Martin also claims that the COVID-19 vaccines are intended to make people sick by converting cells into “a pathogen-manufacturing site”, but he does not support his claim with any evidence. A pathogen is a disease-causing microorganism, like bacteria, fungi, and viruses.

However, this is implausible with the mRNA technology used by the Pfizer-BioNTech and Moderna vaccines. Both vaccines deliver a “blueprint” (mRNA) to cells, which instructs cells on how to make the spike protein that is present on the virus causing COVID-19. This helps the immune system build its defenses in the event of a future encounter with the actual virus, thereby protecting vaccinated individuals from disease. But the vaccines don’t contain the virus’ entire genome and don’t contain the actual virus. Therefore, the vaccines cannot cause cells to manufacture the actual virus, as Martin claims.

Both vaccines produce side effects, such as headaches, fatigue, and muscle aches, which are mild and short-lived compared to the risks associated with getting the actual disease. The FDA reviewed evidence from clinical trials and concluded that the COVID-19 vaccines are generally safe, although anaphylaxis, or a severe allergic reaction is a serious side effect of both COVID-19 vaccines that came to light after they were authorized for emergency use. For this reason, people with a history of severe allergies are advised not to take the vaccines yet. However, anaphylaxis is relatively rare—for the Pfizer-BioNTech vaccine, a joint report by the CDC and FDA found 11 cases of anaphylaxis per million doses, according to the Vaccine Adverse Events Reporting System^[1].

Conclusion

In summary, it is false to state that the CDC and the FDA define a vaccine as a substance that must prevent both disease and transmission. In fact, the CDC and the FDA clearly explain that the purpose of a vaccine is to prevent disease in vaccinated individuals. Neither agencies stipulate that a vaccine must also prevent transmission to be considered a vaccine.

The assertion that the COVID-19 vaccine doesn’t stop transmission is also unsupported, as there simply isn’t enough information at the moment to know whether the vaccines stop (or don’t stop) transmission. Researchers are currently addressing this question, but finding an answer will take time. Meanwhile, it remains important for people to continue using preventative measures, such as maintaining good hand hygiene, wearing face masks, and practicing physical distancing.

REFERENCES

• 1 – CDC COVID-19 Response Team and Food and Drug Administration. (2021) Allergic Reactions Including Anaphylaxis After Receipt of the First Dose of Pfizer-BioNTech COVID-19 Vaccine — United States, December 14–23, 2020. Mortality and Morbidity Weekly Report.

CORRECTION (28 Jul. 2021)

The date that Martin’s livestream video was recorded was corrected to 5 January 2021.