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I've found some papers which describe that the viral shedding does not decrease during infection (for fully vaccinated people). But the overall shedding time does decrease. Therefore it is possible to say, that the vaccines could have a positive effect on the whole pandemic. (They lead to a reduced spread of the disease.)

My question is now: are vaccinated people more likely to not get infected at all?

I've read that the vaccines lead to a shift from severe cases to mild cases, but is there evidence that the vaccines can actually protect people from getting infected?

If someone knows more, could you provide me a source?

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    $\begingroup$ You need to define "not get infected at all" more precisely. Being vaccinated does not stop the virus from entering your body, and may not prevent some of your cells from being infected. However, it (almost always) ensures that enough targeted anti-viral molecules and cells are circulating in your body that they can quickly clear virions and infected cells, resulting in no noticeable illness. $\endgroup$
    – Armand
    Commented Sep 30, 2021 at 1:56
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    $\begingroup$ @Armand Wouldn't it be safe to assume he means not get an active infection? $\endgroup$
    – Brett
    Commented Oct 4, 2021 at 15:18
  • $\begingroup$ The CDC puts the rate as 5x more likely to be infected if unvaccinated: cdc.gov/mmwr/volumes/70/wr/mm7037e1.htm $\endgroup$
    – Brett
    Commented Oct 4, 2021 at 15:22
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    $\begingroup$ @Armandt, its hard to come up with a definition. But than I would say something like "not beeing able to infect other people, because the virus is not able to increase within the host." $\endgroup$
    – Mourinho_1
    Commented Oct 14, 2021 at 20:53

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Yes, this is the effect of the vaccine. A reduction of infections of over 88%, a reduction of severe cases and death by 95% and higher. See reference 1 for the details. Data from the ReCoVAM Study from Malaysia (unfortunately only not yet published, so see here) shows a reduction of infection by 88% and a reduction of admission to ICU/death by up to 96%. So yes, the vaccination works pretty well.

Although symptomatic cases have a comparable viral load in the first four days of their infection this decreases very fast after day four. The figure below (from reference 2) shows this nicely.

enter image description here

The curves show the Ct-values of the PCR from infected patients. The Ct value is the cycle at which the PCR machine can detect a signal from the amplification reaction for the first time. Due to the nature of PCR, the Ct value is inversely proportional to the log of the amount of DNA set into the reaction. The lower the Ct value (the fewer cycles to first detection), the higher the amount of target DNA originally in the sample.

Please note that this comparison is done by PCR and does not give any evidence how infectious the virus from vaccinated people really is. There is evidence (unfortunately from an underpowered study, so results should still be taken with care) that the viruses coming from symptomatic vaccinated people are not as infectious as from unvaccinated persons. See reference 3.

References:

  1. Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data
  2. Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine-breakthrough infections: a multi-center cohort study
  3. Longitudinal analysis of SARS-CoV-2 vaccine breakthrough infections reveal limited infectious virus shedding and restricted tissue distribution
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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – AliceD ♦
    Commented Oct 2, 2021 at 14:49

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