This 2018 Collective Evolution article claims:

Once recent study, however, did bother to look at the question of whether the vaccine prevents transmission. Published on January 18, 2018, in the journal of the Proceedings of the National Academy of Sciences of the United States of America, PNAS, the study’s authors screened volunteers with confirmed cases of influenza and took breath samples. And among their findings was “an association between repeated vaccination and increased viral aerosol generation” [...]

In fact, subjects who had received the influenza vaccine in both the current and the previous season were found to shed over six times more aerosolized virus than those who did not get a flu shot during either season.

Do people who receive flu shots shed the virus more than people who don't?

A grain of truth, but not fully confirmed

The claim...

In fact, subjects who had received the influenza vaccine in both the current and the previous season were found to shed over six times more aerosolized virus than those who did not get a flu shot during either season.

...is clear enough to examine and the author has sourced it well. The source is this article: Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community

The title (boldface mine)...

"Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community"

...and the following must be noted (boldface mine):

We screened 355 volunteers with acute respiratory illness; the 178 volunteers who met enrollment criteria provided 278 visits for sample collection. We confirmed influenza infection in 156 (88%) of the enrolled participants using qRT-PCR

In other words: this study concerns people that at the time were sick with influenza.

The article then states...

Self-reported vaccination for the current season was associated with a trend (P < 0.10) toward higher viral shedding in fine-aerosol samples; vaccination with both the current and previous year’s seasonal vaccines, however, was significantly associated with greater fine-aerosol shedding in unadjusted and adjusted models (P < 0.01). In adjusted models, we observed 6.3 (95% CI 1.9–21.5) times more aerosol shedding among cases with vaccination in the current and previous season compared with having no vaccination in those two seasons. Vaccination was not associated with coarse-aerosol or NP shedding (P > 0.10). The association of vaccination and shedding was significant for influenza A (P = 0.03) but not for influenza B (P = 0.83) infections (Table S4).

So the authors of the study state that...

• in this particular study


• for people that were currently sick with influenza


• for only one type of influenza


• regarding only fine aerosols


• where the subjects said they had been vaccinated

...they measured increased shedding. But for another type of influenza, for other types of shedding, they did not detect that, even in people that were vaccinated before. Also note that the Confidence Interval is — at least in my opinion — quite large. The increase is not actually exactly 6.3 times more for 100% certain, but instead the authors are 95% certain it is somewhere between 1.9 times and 21.5 times more shedding.

So the claim in Collective Evolution has a small grain of truth: in one study they found that for one particular type of influenza, where people had become ill in influenza, and where they had gotten ill despite vaccination, they detected a two-to-twentytwo(ish)-fold increased of shedding in fine aerosols, but not for other types of pathways for shedding. And for the other type of influenza they did not find an increase in fine aerosol shedding.

In the "discussion" section, the authors of the study therefore say the following (boldface added by me):

The association of current and prior year vaccination with increased shedding of influenza A might lead one to speculate that certain types of prior immunity promote lung inflammation, airway closure, and aerosol generation. This first observation of the phenomenon needs confirmation. If confirmed, this observation, together with recent literature suggesting reduced protection with annual vaccination, would have implications for influenza vaccination recommendations and policies.

So the claim in Collective Evolution that it has been proven that for all influensas, all types of aerosol shedding increase if the subject is vaccinated, no matter if they got ill or not, is not supported by this study. The author has ripped out a small section of the original study and extrapolated in ways that are not supported by the study.

Summary

The claim has a grain of truth, in that one study has observed this effect, for people that were vaccinated and still got ill, and only once. But the general claim — that for all influenzas, all vaccinated people increase their virus shedding six-fold — has not been proven. And it is not shown that such shedding warrants a change in policy regarding vaccination.

How did the claim become so wrong?

The claim is posted in an article on Collective Evolution.

Collective Evolution is described by RationalWiki as:

...a woo-mongering clickbait website.

The author is a guest editor that links back to World Mercury Project / Children's Health Defence. Clicking your way in there makes you find even more of that sort.

So what we have is (yet another) case of a scientific study where the participants made a measurement and reported their findings accurately, all in good faith and with rigour. And then the woo-community got wind of the study, ripped one statement out of its context, stripped away all qualifiers and caveats, generalised that statement in a way that is not supported by the scientific study, and started publishing on the Internet.

PhD Comics: Science News Cycle

The claim may be indeed a bit premature to confirm as either true or not true, for the general outlook. It is a robust correlational finding. Explanations of causation may follow, if confirmed. But it cannot and mustn't be dismissed out of hand.

But the finding is a valid one and the outlet from which we came here reported not that much exaggerated as perhaps to be expected, following a guild by association approach for that particular outlet!*

The original study reads in its abstract:

We provide overwhelming evidence that humans generate infectious aerosols and quantitative data to improve mathematical models of transmission and public health interventions. We show that sneezing is rare and not important for—and that coughing is not required for—influenza virus aerosolization. Our findings, that upper and lower airway infection are independent and that fine-particle exhaled aerosols reflect infection in the lung, opened a pathway for a deeper understanding of the human biology of influenza infection and transmission. Our observation of an association between repeated vaccination and increased viral aerosol generation demonstrated the power of our method, but needs confirmation.
_{Yan J et al.: "Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community.", Proc Natl Acad Sci U S A. 2018 Jan 30;115(5):1081-1086. doi: 10.1073/pnas.1716561115.}

That is **Fine-aerosol viral RNA was also positively associated with having influenza vaccination for both the current and prior season. **

That are two new findings in this study:

1. and more important, there was apparently no ned to cough and sneeze to spread infection.


2. "The association of current and prior year vaccination with increased shedding of influenza A might lead one to speculate that certain types of prior immunity promote lung inflammation, airway closure, and aerosol generation. This first observation of the phenomenon needs confirmation. If confirmed, this observation, together with recent literature suggesting reduced protection with annual vaccination, would have implications for influenza vaccination recommendations and policies."

Although point 2 is indeed ripe with speculation, these are plausible.

Other authorities evaluate the claim as such:

Ashley York: "Breathing alone may spread the flu", Nature Reviews Microbiology volume 16, page 123 (2018):
Influenza viruses have been proposed to spread through aerosols, but the importance of this mode of transmission between humans is unclear. Now, Yan et al. provide evidence that humans generate infectious aerosols by characterizing the virus in exhaled breath during natural breathing, prompted speech, coughing and sneezing. By analysing paired nasopharyngeal and breath samples from infected individuals, the authors observed that a significant proportion of the infected individuals shed infectious virus in aerosol particles that have the potential to spread by aerosol transmission (≤5 μm). Surprisingly, coughing and sneezing was not necessary for the generation of infectious aerosols, and sneezing did not increase the amount of viral RNA in aerosol particles. The authors argue that these findings could be used to improve models of airborne influenza virus transmission.

Richard T. Ellison III, MD: "Airborne Influenza Transmission", NEJM Journal Watch, 2018:

Infectious virus was present in 89% of the NP samples and 39% of fine aerosol samples. Geometric mean RNA copy numbers for fine and coarse aerosol samples were 3.8×104 and 1.2×104 per 30 minutes, respectively, compared with 8.2×108 per NP swab. The amount of viral shedding in fine aerosol samples declined with the number of days after symptom onset and was increased for males and with coughing, although shedding occurred without coughing or sneezing. Self-reported flu vaccination in both the 2012–2013 and previous flu seasons was associated with fine aerosol shedding but not NP or coarse aerosol shedding.

COMMENT

This study supplements prior evidence supporting the risk for influenza transmission by fine aerosols and will renew discussions regarding the optimal approach to protecting healthcare providers from acquiring the virus (NEJM JW Infect Dis Nov 2009 and JAMA 2009; 302:1865). The authors acknowledge that the unexpected observation of increased fine aerosol shedding in vaccine recipients requires confirmation in additional studies.

And even more interesting a BMJ article trying to make sense of this:

“Self-reported vaccination for the current season was associated with a trend (P < 0.10) toward higher viral shedding in fine-aerosol samples; vaccination with both the current and previous year’s seasonal vaccines, however, was significantly associated with greater fine-aerosol shedding in unadjusted and adjusted models (P < 0.01). In adjusted models, we observed 6.3 (95% CI 1.9–21.5) times more aerosol shedding among cases with vaccination in the current and previous season compared with having no vaccination in those two seasons.” [7⁠]

This result makes a lot of sense. When you have influenza virus allergy and are infected, you have more mast cell degranulation, more histamine, more mucus, more sneezing, more viral shedding.

Increased hospitalization rates have been observed in asthma patients that have received the influenza vaccine. Again, this is as predicted because asthma patients are likely to produce stronger IgE responses to the viral proteins upon vaccination. On subsequent virus exposure, they can be expected to develop severe IgE mediated asthma.

MEPs devise strategy to tackle vaccine hesitancy among public, BMJ 2018; 360 doi: https://doi.org/10.1136/bmj.k1378 (Published 23 March 2018) BMJ 2018;360:k1378

It seems they do spread more virus than healthy people.

But...

We're missing two very important pieces of data, here.

1. Do the shed virus have same risk as virus shed by an actually sick person, or might they be shedding the weakened or sick virus used with the vaccine, in effect helping to vaccinate others and increasing herd immunity?


2. I only see a comparison with healthy people. How does this compare with a person who is actual "sick" with influenza? Six times more than a healthy person seems really bad, but if the a sick person is shedding, say, 600 times more virus, that might still be a net positive for a community to have people vaccinated, as you'd need to come in contact with 100 vaccinated people to have the same exposure as with one sick person. But what are the actually numbers? We don't know yet, and it probably varies significantly depending on what strain of virus the sick person has.