Asymptomatic Spread by Vaccinated Persons

Vaccinated persons present a higher coronavirus transmission risk than unvaccinated persons starting a few months from vaccination.


COVID-19 vaccines are injected intramuscularly and produce systemic immunity (Bleier, Ramanathan, and Lane 2021). They do not produce strong or long-lasting mucosal immunity (Tiboni, Casettari, and Illum 2021), which is another part of the natural immune response to infection, even an asymptomatic one. (Russell et al. 2020) provides a mucosal immunity review.

It was known from the start that the current COVID-19 vaccines do not provide sterilizing immunity. Another known fact is that even in vaccinated persons, the coronavirus can infect mucosal surfaces of the upper respiratory tract for at least a short time, where it can grow and be shed before being neutralized by the systemic immunity. It seemed not a major factor at the start of the vaccines roll out. Nevertheless, it was predicted that the rise of vaccine resistant and more infectious variants would create the problem of asymptomatic shedding from vaccinated persons (Goldstein 2021).

This has happened and was confirmed by direct measurements (Chia et al. 2021). This study found that vaccinated persons have the same initial viral load as unvaccinated ones, as tested by nasal swab. In the same group, the vaccinated persons were three times more frequently asymptomatic than unvaccinated ones. When symptomatic, vaccinated persons had fewer symptoms than unvaccinated persons, thus making the disease harder to notice.

Notably, SARS-COV-2 does not need to induce symptoms like coughing or sneezing in a host to make it to another host, so nothing prevents asymptomatic spread.

Inaccurate information provided by the CDC, other government agencies, and their mouthpieces is likely to contribute to COVID-19 spread by vaccinated persons, especially when their antibodies immunity has waned since the vaccination. A vaccinated person infected without symptoms would not recognize the infection. A vaccinated person with mild symptoms might not recognize SARS-COV-2 under the false belief that vaccination still protects him/her from getting sick with COVID-19. A vaccinated person might be reluctant to self-isolate based on the idea that s/he has done enough for society by taking the vaccine. A vaccinated person might also be under the false belief that wearing a mask by him/her or by persons around protects them from infection. Masks are useless in prevention COVID-19 transmission, unless used intently in healthcare settings.

Older age (Chia et al. 2021) and longer time since vaccination are expected to be independent risk-increasing factors. Older people are also likely to be around other older people.

It is hardly necessary to restate that younger people are at a low risk of severe COVID-19. It might be expected that a vaccinated person would acquire at least mucosal immunity after exposure to SARS-COV-2. Further, most people had some immunity to COVID-19 before vaccination. Thus, the danger of infection from vaccinated persons should not be exaggerated.

Of note, many vaccines provide sterilizing immunity. For flu vaccines, the preferred route is intranasal (“Quadrivalent Influenza Vaccine | CDC” 2021), which is intended to elicit mucosal immunity.

Suppression of scientific information negative to vaccination

I noticed that many research papers reporting negative outcomes of COVID-19 vaccines and mass vaccination also include language vaccination, sometimes contradicting the reported outcomes. That suggests the suppression of negative scientific information about COVID-19 vaccines. That, in turn, suggests the suppression of research that is likely to lead to negative results for vaccines and mass vaccination.

Some Relevant Quotes

(Bleier, Ramanathan, and Lane 2021) : “Current COVID-19 vaccine candidates are administered by injection and designed to produce an IgG response, preventing viremia and the COVID-19 syndrome. However, systemic respiratory vaccines generally provide limited protection against viral replication and shedding within the airway, as this requires a local mucosal secretory IgA response. Indeed, preclinical studies of adenovirus and mRNA candidate vaccines demonstrated persistent virus in nasal swabs despite preventing COVID-19. This suggests that systemically vaccinated patients, while asymptomatic, may still be become infected and transmit live virus from the upper airway.”

(Cohen 2021) in Forbes: “Second, and important in terms of viral spread, vaccinated individuals who get breakthrough Delta variant infections can and do transmit the coronavirus to others.”

“Virologists at several of the Netherlands’ leading academic medical centers have observed that fully vaccinated healthcare workers who contract coronavirus can transmit it, whether they are symptomatic or asymptomatic. Transmission can take place from fully vaccinated to partially and unvaccinated persons, but also between fully vaccinated persons.”

(Chia et al. 2021): “Vaccine-breakthrough patients were significantly more likely to be asymptomatic (28.2% versus 9.2%, p<0.001); and if symptomatic, had fewer number of symptoms”

“In line with Singapore’s national vaccination strategy wherein older adults were prioritized for vaccination, our vaccine-breakthrough cohort was of significantly older age; median age of 56 years (IQR:39-64) versus 39.5”

“initial viral load indicated by PCR Ct values was similar between vaccinated and unvaccinated patients with B.1.617.2”

“we provide the first data characterizing impact of vaccination on virologic kinetics by the B.1.617.2 variant. While initial Ct values were similar; the effect of vaccination with a more rapid decline in viral load (and hence shorter duration of viral shedding) has implications on transmissibility and infection control policy”


Bleier, Benjamin S., Murugappan Ramanathan, and Andrew P. Lane, 2021, “COVID-19 Vaccines May Not Prevent Nasal SARS-CoV-2 Infection and Asymptomatic Transmission,” Otolaryngol Head Neck Surg (SAGE Publications Inc)

Chia, Po Ying, Sean Wei Xiang Ong, Calvin J. Chiew, Li Wei Ang, Jean-Marc Chavatte, Tze-Minn Mak, Lin Cui, et al., 2021, “Virological and Serological Kinetics of SARS-CoV-2 Delta Variant Vaccine-Breakthrough Infections: A Multi-Center Cohort Study,” medRxiv (Cold Spring Harbor Laboratory Press), 2021.07.28.21261295,

Cohen, Joshua, 2021, “Among Fully Vaccinated, Breakthrough Covid-19 Infections Are More Common Than Previously Thought: Does It Matter? [Update],” Forbes, Accessed August 7,

Goldstein, Leo, 2021, “Guided Evolution of the Coronavirus,” Science Defies Politics, Accessed August 5,

“Quadrivalent Influenza Vaccine | CDC,” 2021, May 6,

Russell, Michael W., Zina Moldoveanu, Pearay L. Ogra, and Jiri Mestecky, 2020, “Mucosal Immunity in COVID-19: A Neglected but Critical Aspect of SARS-CoV-2 Infection,” Front. Immunol. (Frontiers)

Tiboni, Mattia, Luca Casettari, and Lisbeth Illum, 2021, “Nasal Vaccination against SARS-CoV-2: Synergistic or Alternative to Intramuscular Vaccines?,” Int J Pharm

Originally published on 2021-08-08. Corrected on 2021-08-09.

4 thoughts on “Asymptomatic Spread by Vaccinated Persons

  1. Trying to understand the mucosal immunity aspect. If the vaccine does not provide mucosal immunity can someone explain how the Moderna vaccine is 75% effective and the Pfizer vaccine is 46% effective at preventing you from catching COVID?

    1. These vaccines elicit systemic immunity – antibodies & T-cells that neutralize the virus when it passed the mucosal surfaces. The effectiveness numbers vary depending on what is measured – infection, mild disease, severe disease etc. These vaccines do not prevent infection, except for maybe a few weeks after getting ‘fully vaccinated’

  2. Regarding infected asymptomatic vaccinated individuals, is there any idea of how long they could potentially be transmitting the virus? Is it plausible that they would remain asymptomatic until the protection mechanisms of the vaccine began to wane?

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