old is gold: live-attenuated Covid vaccines prevent transmission
When it comes to health/medicine, "old is gold" is a good thumb rule because old stuff have much has survived the test of time, the most rigorous test of long-term safety. Often, they even have much better efficacy evidence, but are still ignored for various reasons: profitability, many academics need too cook up some complex new stuff to advance their careers and delude the world with hype: application of old techniques to new problems isn’t considered as sexy in academia as inventing new techniques.
Perhaps the best example is live-attenuated vaccines, the oldest vaccine technology: they eradicated smallpox and eliminated polio from most of the world. Later, live vaccines were found not just to prevent the target disease, but also teach the immune system to fight unrelated diseases. For example, the measles vaccine was found to lower deaths by 5x as many measles deaths. Recently, a RCT found the BCG vaccine (live vaccine) be effective in reducing Covid illness diagnosed by symptoms and/or antigen tests.
One live-attenuated vaccine for Covid seem to be doing much better than the mrna or adenovirus vaccines, especially for preventing transmission of Covid, at which the existing vaccines seem dismal:
Animals were vaccinated with a single dose of the respective recoded virus and challenged 21 days later. Two of the tested viruses do not cause clinical symptoms but are highly immunogenic and induce strong protective immunity. Attenuated viruses replicate efficiently in the upper but not in the lower airways, causing only mild pulmonary histopathology. After challenge, hamsters develop no signs of disease and rapidly clear challenge virus: at no time could infectious virus be recovered from the lungs of infected animals. The ease with which attenuated virus candidates can be produced and administered favors their further development as vaccines to combat the ongoing pandemic.
Note that these are not human trials, but measuring reduction in transmission is very difficult to do in human trials: human subjects would not like to be challenged (deliberately infected) with the Covid virus and then have lung tissue samples take frequently to measure infectivity. None of the human trials of the approved Covid vaccines showed reduction in transmission, and data from the real world shows dismal if any efficacy in reducing transmission, especially during the first 6 days of the infection. Indeed, in animal trials, the Astrazeneca Covid vaccine failed to stop infections, although it probably did reduce the severity. As far as I know, Moderna didn’t even do such studies to measure reduction of transmission in animals.
So, why are we not investing much more time and effort in live-attenuating Covid vaccines — a centuries tested technology with success in eradicating diseases, the claimed goal of many Covid “experts“ — and instead doubling down on the mrna vaccines with unknown long-term safety and problematic short-term safety signals, e.g. myocarditis in young boys? I think the guess of @gerdosi is correct:
One drawback of live-attenuated-vaccines is that they may cause disease in immuno-compromised people. But the mrna vaccines dont appear to be effective in such people either, so we can just avoid vaccinating such people and instead vaccinate the people who live with them with live-attenuated Covid vacccines that appear to prevent transmission completely.
[UPDATE]: live-attenuated Covid vaccines may not work in those who already got the Covid mrna vaccines:
Interesting write up!