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Note that we still don't have much data on whether and by how much vaccinations do reduce transmission. The objective of the vaccines was to minimize serious ca

Note that we still don't have much data on whether and by how much vaccinations do reduce transmission. The objective of the vaccines was to minimize serious cases. But transmissions are a different story. It could easily be that the vaccine prevents serious cases in 95% of people but transmission is not impacted significantly. We just don't know yet. Why is this relevant? Because the whole concept of "herd immunity" is only about transmission.

Tomte 6y ago
For BioNTech it looks good: https://www.bloomberg.com/news/articles/2021-02-21/pfizer-biontech-shot-stops-covid-s-spread-israeli-study-shows https://www.bloomberg.com/news/articles/2021-02-21/pfizer-bi...
tsimionescu 6y ago
Minor quibble: the vaccines were tested on their ability to minimize symptomatic cases of any kind, not just serious cases. In fact, the Pfizer study didn't have any data on serious cases at all (they had a total of 4 serious cases, one in the vaccine group, three in the control group - not enough to make any prediction at all on the effect against serious cases. The other studies fare a little better, but we know a lot more about the effects on any kind of Covid19 than on serious cases, or on transmission of SARS-COV-2 itself.
sneak 6y ago
A side question: the vaccines have been out for months. Why is there no data on whether or not they affect transmission? That seems like something that could be figured out within a week or two of the vaccine being finalized. I have been worrying that the now all too familiar "we still don't know if the vaccine prevents transmission" is just a stand in for saying "it doesn't". Every additional week makes me less hopeful.
- jsnell 6y ago
  > That seems like something that could be figured out within a week or two of the vaccine being finalized. Just what kind of a study do you think could do that within "a week or two"?
- iainmerrick 6y ago
  How would you go about figuring that out? What the trials have mostly been checking so far is “does the vaccine prevent serious illness”, and they measure that by counting occurrences in the test group vs placebo group. Very straightforward, which is why it’s possible to do it fairly quickly.
reissbaker 6y ago
This is no longer true. We do have data that the vaccines reduce transmission, thanks to Israel's mass vaccination program: https://www.reuters.com/article/health-coronavirus-israel-vaccine-int-idUSKBN2AJ08J https://www.reuters.com/article/health-coronavirus-israel-va... The margin of reduced transmission is very close to the margin of reduced symptoms: 90% reduction in asymptomatic transmission, and 93% reduction for symptomatic transmission. The study is only on Pfizer's vaccines, but I would expect Moderna's to perform similarly, since they're both MRNA vaccines targeting the spike protein and they have similar effectiveness at reducing symptoms.
- ganafagol 6y ago
  Excellent! Thanks for the link. This needs more studies but it's a promising data point. I'm surprised that these studies come so late. Vaccination strategies need to be quite different depending on their outcomes.
- rotexo 6y ago
  Careful there—those conclusions may be overstated because of bias in the people getting tested in vaccinated vs. unvaccinated groups (https://mobile.twitter.com/ZoeMcLaren/status/1363582050775744515 https://mobile.twitter.com/ZoeMcLaren/status/136358205077574...)
tinus_hn 6y ago
And, of course the measurements are about false positives. If you are vaccinated and then come in contact with someone who is infected, do you test positive? Nobody knows, really. And people you are in contact with? Unknown.

Tomte 6y ago

For BioNTech it looks good: https://www.bloomberg.com/news/articles/2021-02-21/pfizer-biontech-shot-stops-covid-s-spread-israeli-study-shows https://www.bloomberg.com/news/articles/2021-02-21/pfizer-bi...

tsimionescu 6y ago

Minor quibble: the vaccines were tested on their ability to minimize symptomatic cases of any kind, not just serious cases. In fact, the Pfizer study didn't have any data on serious cases at all (they had a total of 4 serious cases, one in the vaccine group, three in the control group - not enough to make any prediction at all on the effect against serious cases. The other studies fare a little better, but we know a lot more about the effects on any kind of Covid19 than on serious cases, or on transmission of SARS-COV-2 itself.

sneak 6y ago

A side question: the vaccines have been out for months. Why is there no data on whether or not they affect transmission? That seems like something that could be figured out within a week or two of the vaccine being finalized. I have been worrying that the now all too familiar "we still don't know if the vaccine prevents transmission" is just a stand in for saying "it doesn't". Every additional week makes me less hopeful.

jsnell 6y ago
> That seems like something that could be figured out within a week or two of the vaccine being finalized. Just what kind of a study do you think could do that within "a week or two"?
iainmerrick 6y ago
How would you go about figuring that out? What the trials have mostly been checking so far is “does the vaccine prevent serious illness”, and they measure that by counting occurrences in the test group vs placebo group. Very straightforward, which is why it’s possible to do it fairly quickly.

reissbaker 6y ago

This is no longer true. We do have data that the vaccines reduce transmission, thanks to Israel's mass vaccination program: https://www.reuters.com/article/health-coronavirus-israel-vaccine-int-idUSKBN2AJ08J https://www.reuters.com/article/health-coronavirus-israel-va... The margin of reduced transmission is very close to the margin of reduced symptoms: 90% reduction in asymptomatic transmission, and 93% reduction for symptomatic transmission. The study is only on Pfizer's vaccines, but I would expect Moderna's to perform similarly, since they're both MRNA vaccines targeting the spike protein and they have similar effectiveness at reducing symptoms.

ganafagol 6y ago
Excellent! Thanks for the link. This needs more studies but it's a promising data point. I'm surprised that these studies come so late. Vaccination strategies need to be quite different depending on their outcomes.
rotexo 6y ago
Careful there—those conclusions may be overstated because of bias in the people getting tested in vaccinated vs. unvaccinated groups (https://mobile.twitter.com/ZoeMcLaren/status/1363582050775744515 https://mobile.twitter.com/ZoeMcLaren/status/136358205077574...)

tinus_hn 6y ago

And, of course the measurements are about false positives. If you are vaccinated and then come in contact with someone who is infected, do you test positive? Nobody knows, really. And people you are in contact with? Unknown.