Comment by defrost | Hacker News Reader

Comment by defrost | Hacker News Reader

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Yes, they do reduce transmission.

For example (and there are many):

    Data from studies in the United Kingdom showed that both the Pfizer and AstraZeneca COVID-19 vaccines were effective in preventing onward transmission of the virus to close contacts in case of breakthrough infections.

    In one study among the general population in the United Kingdom, the effectiveness against transmission from breakthrough infections to household contacts from 21 days after the first dose was 47% (95% CI: 37–57) for the AstraZeneca COVID-19 vaccine and 49% (95% CI: 41–56) for the Pfizer COVID-19 vaccine. [1]

    Another study from the United Kingdom reported that, among healthcare workers, who predominantly received the Pfizer COVID-19 vaccine, vaccination was associated with a 30% (95% CI: 22–37) reduction in transmission of SARS-CoV-2 to household contacts. [2]

[1] Harris RJ, Hall JA, Zaidi A, et al. Impact of vaccination on household transmission of SARS-COV-2 in England. 2021.

[2] Shah ASV, Gribben C, Bishop J, et al. Effect of vaccination on transmission of COVID-19: an observational study in healthcare workers and their households (preprint). medRxiv 2021.

Please read my comment again. I specifically said "delta".

The first study you mentioned is:

https://khub.net/documents/135939561/390853656/Impact+of+vac...

This is a study of less than 2 months between "4 January 2021 to 28 February 2021". This is long long before delta and omicron and newer variants came. I specifically mentioned the changes which Delta brought.

Second study you cited is:

https://www.medrxiv.org/content/10.1101/2021.03.11.21253275v...

This is once again an outdated study from "8th December 2020 to 3rd March 2021" which is long before Delta, Omicron, and newer variants.

People repeatedly keep citing outdated studies from before Delta, Omicron and don't acknowledge the changes which those variants plus waning immunity brought. Also any study which doesn't measure asymptomatic infections is worthless.

Here's a better example. In a 94% vaccinated study, 56% reported being unaware of their infection:

https://jamanetwork.com/journals/jamanetworkopen/fullarticle...

What happens when infected people go around not knowing they are infected? They infect others and have a false sense of safety.

Seroprevalence data also shows 90% of population has already been infected. If the vax was preventing transmission, that wouldn't be happening.

I initially responded to an overly broad generic comment

" Since the vaccines didn’t stop transmission, can’t the same be said of them? "

with the broadly true statement that no vaccine that I'm aware of stops transmission .. they ideally reduce transmission* (being effectively not a vaccine if they fail to slow spread through a population (or mitigate effects of a virus that does spread)).

The studies I cite are just two (of many) first off the rank that demonstrate that the two of the more widely used vaccines did indeed slow transmission at the time they were used.

> Here's a better example. In a 94% vaccinated study, 56% reported being unaware of their infection:

I read that with interest the entire way through,

* it fails to support a claim that "vaccines did not reduce transmission of Delta or Omicron variants"

* it supports a claim that "vaccines reduced the effect of having a COVID variant (to the degree that most did not even realise they'd been infected)"

The specific statistical reason that your "better example" doesn't address the transmission rate (through vaccinated Vs unvaccinated populations) is that it exclusively looks at people infected and the bulk of those are vaccinated.

There's no larger view there of infection rates in a bigger population, and no differential look at infection rates in unavaccinated Vs vaccinated.

What the study confirms (re: transmission) is something I conceded in my first coment: vaccines do not stop transmission

(again, they ideally reduce transmission rates (not addressed in your 'better' study)).

If you're interested in a longwinded careful, multi factor analysis and model type paper (of which there are many) one such example is

https://www.frontiersin.org/articles/10.3389/fpubh.2022.8230...

which is detailed but lacks any clearcut gotcha messages .. it bears close reading and laments in places the lack of early vaccine uptake in the population (Australia) during the Delta and Omnicron waves (ie. supports vaccines reducing transmission rates, doesn't dwell on it as not enough people are vaccinated at that time and so looks at other mitigations).

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