This is the new “we have no evidence masks help” or “no evidence of asymptomatic spread”.
Name a vaccine that doesn’t reduce onward transmission even as it cures disease. It’s overwhelmingly likely that the vaccine will slow transmission and foolish to throw our priors in the garbage bin.
What we don’t know yet is how much onward transmission will be reduced.
I looked into this, and it does seem the vaccine reduces transmission. It just doesn’t stop it entirely. The paper below is Wikipedia’s source. Upon a close read, in the daycare there were three groups of vaccinated children:
* Those positive for antibodies but pcr negative —> had been exposed, cleared virus without infection
* those pcr positive but asymptomatic
* those pcr positive and symptomatic
About 30% were in the seropositive group which didn’t have pcr positivity. So it seems like transmission was reduced at least 30%. It’s also possible the other two groups would have had lower transmission rates than if they had had no vaccine.
If you have a more precise source I’d be interested to see it, but if this is the worst case it’s pretty good!
> We used PCR, EIA, and culture to confirm B. pertussis infection in two highly vaccinated groups of children in two day-care centers. Three (10%) of 30 2- to 3-year-old children were seropositive for recent infection; one had nasopharyngeal colonization and a clinical illness that met the modified WHO case definition. In the day-care center for the 5- to 6- year-old group, 9 (55%) of 16 children were IgM positive, 4 (25%) of whom had nasopharyngeal colonization. Of these four children, three had nonspecific cough, and only one met the modified WHO definition for pertussis. None of the children in our study, including those who met the WHO definition, had been examined by a physician before our investigation.
>Children who were seropositive and re- mained both asymptomatic and PCR negative probably had sufficient immunity from vaccines or natural boosters to protect them against persistent colonization and clinical disease. Their seropositivity could not be due to vaccine because the children were tested more than a year after having been vaccinated.
> In this paper they've used 45 for HIV. What's your point?
There is a difference between HIV vs SARS-Cov2: If you get AIDS, your body does not have the capacity to recover from it on its own. So, 1) the chances of detecting dead material from a long gone infection are nil; and 2) the cost of a false negative is much higher than the cost of a false positive.
Since most people seem not to be seriously affected by a SARS-Cov2 infection, neither is true for SARS-Cov2. So, not agreeing on a fixed, reasonable, standard number of cycles which everyone uses has the consequence of inflating false positives for no gain. Note WHO's updated information[1].
> WHO guidance Diagnostic testing for SARS-CoV-2 states that careful interpretation of weak positive results is needed (1). The cycle threshold (Ct) needed to detect virus is inversely proportional to the patient’s viral load.
If you are not sick and your viral load is barely detectable, what's the point?
So you think they should use some lower Ct number for which it would be possible to show that eg 99.5% of people who are over it (i.e. have lower viral load) don't infect anyone? Interesting. I've read that most of the false negative for a PCR test actually come from sample collection (makes sense, PCR is super reliable) so it could be that you would miss people with high viral load where the sample was just not taken in a perfect way. Especially early in the infection it could be quite localized.
> So you think they should use some lower Ct number
Everyone should use the same number in all tests. From what I understand, about 20 is a reasonable number which might still result in positives up to a month post-infection. I consider having a standard more important that the specific number chosen. It seems when people go to > 30 it is in a quest to ensure a positive test result.
I fail to see what this has to do with vaccines and infectivity.
Also I’d only heard of people speak in terms of “positive” for pcr. You can be positive but not infectious, if there are a lot of cycles and you’re tested as the disease winds down.
Name a vaccine that doesn’t reduce onward transmission even as it cures disease. It’s overwhelmingly likely that the vaccine will slow transmission and foolish to throw our priors in the garbage bin.
What we don’t know yet is how much onward transmission will be reduced.