Do unvaccinated people carry more COVID cooties?

August 26, 2021 7:52 AM

If we took ten random unvaccinated (for COVID 19) people from the Seattle area, and ten random fully vaccinated people, who would be carrying more COVID viruses? I know the vaccinated people are far less likely to feel sick, but is either group more likely to spread the virus?
posted by The corpse in the library to Science & Nature (12 answers total)

If you took ten random unvaccinated people from the Seattle area who were infected with Covid-19 Delta variant, and ten random vaccinated people from the Seattle area who were infected with Covid-19 Delta variant who all exhibited identical social behaviour, then recent research suggests they would be equally likely to be spread the virus initially.

However, the vaccine does work and has an effect on whether you catch the virus at all. So fewer of your random vaccinated people would actually be infected with the virus. In addition, there is some evidence that vaccinated people are infectious for a shorter period of time. On top of that, in the real world unvaccinated status is somewhat correlated with having more risky behaviours (eg not masking or socially distancing), which makes those people more likely to spread the virus.

Vaccinated people, in theory, can spread the virus equally as well as unvaccinated people for a short period of time after having been infected. In practice, unvaccinated people represent a higher risk of infecting people with Covid-19. How much higher may be difficult to establish yet.

Further research is likely to increase our understanding of the pandemic, and as a result some things that we currently believe to be true will turn out to be inaccurate or oversimplifications.
posted by plonkee at 8:11 AM on August 26, 2021 [13 favorites]

The data interpretations I've seen in the last 10ish days suggests that vaccinated people with the Delta variant hit a similar viral load to unvaccinated, but not for as long as unvaccinated - except I can't find a cite for the duration now, so either I imagined it or it's just really hard to google.
posted by Lyn Never at 8:13 AM on August 26, 2021

How do vaccinated people spread Delta? What the science says - Nature, Aug 12, 2021
A summary article on this with some citations. One part of it says "vaccinated people with Delta might remain infectious for a shorter period, according to researchers in Singapore who tracked viral loads for each day of COVID-19 infection among people who had and hadn’t been vaccinated. Delta viral loads were similar for both groups for the first week of infection, but dropped quickly after day 7 in vaccinated people".

I believe the situation is:
1. The vaccinated people are much less likely (than unvaxxed people) to become infected in the first place if exposed.
2. If they do become infected (i.e. have a "breakthrough case"), then they carry similar viral load to an unvaccinated person who becomes infected.
3. But maybe for a shorter overall time?

From that, I'd expect that given a random sample of vaxxed vs unvaxxed people, there would be more virus in the unvaxxed sample because of 1 and 3.
posted by LobsterMitten at 8:26 AM on August 26, 2021 [4 favorites]

The science on this is rapidly evolving; whatever answers you get right now will be incomplete.
posted by Nelson at 8:29 AM on August 26, 2021 [7 favorites]

The question you asked is not the same question as "does the vaccine reduce the amount of viable virus shed by an infected person?".

In addition to the stuff pointed out by plonkee, above, random vaccinated people are going to be more likely to be careful with respect to contagion in other ways besides just receiving the shot. Even if infected and having the same viral load, they're wearing a goddamn mask and washing their filthy hands and social distancing and limiting trips outside the home to those genuinely necessary.

Unlike the unvaccinated, who are behaving in myriad other stupid plague-enabling ways (beyond the stupid plague-enabling step of being unvaccinated in the first place).

To answer the question you actually asked: The random sample of 10 unvaccinated people are more likely to spread the virus (even if the vaccine in and of itself plays no part in that outcome).
posted by sourcequench at 8:34 AM on August 26, 2021 [4 favorites]

Questions like this are frankly dangerous, because the logic of "unvaccinated and vaccinated people carry the same viral load" is being used by anti-vaccine propagandists to discourage people from getting the vaccine.

The science is incomplete. We don't know the answer.
posted by twelve cent archie at 8:37 AM on August 26, 2021 [3 favorites]

This study just came out - unvaccinated people are more infectious, but 2/3 of vaccinated people are still infectious.
posted by todolos at 8:39 AM on August 26, 2021 [2 favorites]

Ten is a very small sample size. Nearly any result would be possible.
posted by kevinbelt at 9:21 AM on August 26, 2021 [2 favorites]

todolos, that study says 2/3 of vaccinated people WHO HAVE BREAKTHROUGH INFECTIONS shed virus. That is not the same as the "2/3 of vaccinated people" you say. That’s a terrible misrepresentation.
posted by clew at 9:59 AM on August 26, 2021 [6 favorites]

The best explanation I’ve recently heard was last weekend on Al Franken’s podcast, with guest Laurie Garrett. At 12:30, she talks about how the vaccine works:

• When you first receive the vaccination, your body is full of antibodies to fight the virus.
• After a period of time, the antibodies go away, but the memory B cells persist. So that if you are re-infected, your body knows how to regenerate the antibodies.
• Unfortunately, the Delta variant has such a quick incubation period, your body can’t regenerate those antibodies fast enough, so you can still get sick with Covid-19. However, those antibodies will kick in, and your infection will be much, much less severe.

Then later at 19:25 she talks about how those antibodies don’t work as well in the nasal passages and the mouth, and how the evidence seems to indicate that there were people who were vaccinated and asymptomatic but still probably harbored virus in their nasal passages and infected other people. How prevalent is this? It is unclear. But the takeaway is that wearing masks is still important, even if you are vaccinated.
posted by 1970s Antihero at 10:00 AM on August 26, 2021 [1 favorite]

Yes. Based on data from July 18 to August 21, during which time the delta variant made up the vast majority of cases, Ottawa [Canada] Public Health reports based on actual infection rates that the risk of catching COVID-19 is 22 times higher among the unvaccinated vaccine-eligible population than it is for the fully-vaccinated population. (Scroll down to the middle of the page; the data is under the heading "Vaccination Status".) While this is a relatively small sample, Ottawa's testing and contact-tracing regime is currently robust, so that asymptomatic cases among close contacts are being identified and tested. So even if viral loads and infectious periods were identical (probably false), and not making any assumptions about behaviours that are not actually being performed by the population, your unvaccinated people are around 22 times more likely to be carrying COVID cooties than your vaccinated ones.
posted by heatherlogan at 11:36 AM on August 26, 2021 [1 favorite]

In general (before Covid), the accepted thinking was that a virus like a common cold makes its way forward in the world by infecting a host and in the process producing symptoms such as coughing, sneezing, runny nose, etc., all of which allows for the virus to spread actively to others in the air and on solid surfaces. That paradigm probably applies to Covid as well, but sneezing and a runny nose are not really symptoms commonly associated with this one.
posted by yclipse at 7:12 PM on August 26, 2021