4 ms·

Vaccines that prevent disease symptoms but don't completely prevent infection are definitely a thing (they're said to confer "non-sterilizing immunity," vs. "st

Vaccines that prevent disease symptoms but don't completely prevent infection are definitely a thing (they're said to confer "non-sterilizing immunity," vs. "sterilizing immunity" which prevents both infection and disease). The inactivated polio vaccine (the injectable one that's used in the US) is an example of such a vaccine. The oral polio vaccine, which is the main one used in the developing world, interestingly does confer sterilizing immunity, but with the tradeoff that sometimes it also causes polio. At least in the US, the explicit target endpoint for FDA approval was just prevention of disease, not prevention of infection, and the phase III trials for both the Moderna and Pfizer/BioNTech trials were only designed to assess this criterion: they only tested symptomatic people, so it's entirely possible (though not that likely given animal model observations, etc.), that infections were just as common in the treatment groups as control groups, but they just never developed symptoms and so were never tested. More research will be needed to ascertain which kind of immunity is being conferred.

acqq 6y ago
The researchers joke that "animals lie", in the sense that animals can have different reactions compared to humans, in spite of the researchers trying as much as possible to get something useful in the experiments. Having said that, I still believe your claim of what can be concluded to be unlikely based on "animal model observation" is false, from what is known up to now. Specifically: https://www.medscape.com/viewarticle/941030?src=soc_tw_201118_mscpedt_news_mdscp_vaccine&faf=1 https://www.medscape.com/viewarticle/941030?src=soc_tw_20111... "In an ideal world, a vaccine would prevent infection entirely and, it follows, also prevent disease and severe disease. But this may be hard to achieve for a respiratory virus vaccine. Animal challenge data suggest that vaccinated animals may still be infected even if they don't experience symptoms. A vaccine that is able to reduce the severity of disease, even if it cannot prevent infection entirely, would obviously still have enormous public health value. Therefore, this is what trials target as their primary aim." I suggest everybody to read carefully the whole article, as it is written by an indisputable expert, and what is presented in the article isn't based only on the animal models but on much broader knowledge. Nobody at this moment should expect that the vaccines guarantee that somebody who is vaccinated won't be able to infect somebody who hasn't received a vaccine. That, for example, means that even if the health workers do get a vaccine they will still have to wear protective equipment.
- jfoster 6y ago
  Might this also have a silver lining? If the virus is still able to spread, does that mean that it is less likely to face selection pressure to mutate around the vaccines?
  - acqq 6y ago
    Contrary to what is often believed, regarding mutations, coronaviruses behave completely differently than flu viruses. The mutation rate among coronaviruses is so slow that it's much more probable that whenever we see some new significant change among them it is due to the recombination, not due to the mutation. Coronaviruses have a specific mechanism of "error correction" in them which lowers the mutation rate, compared to most RNA viruses. The "selection pressures" are also less likely in this case then most would estimate. We as humans are much more "pressured" by this virus in its current form than the virus by anything we'd do. The viruses themselves don't even "need" to come "around" anything, and there are enough unknown viruses in the world which aren't less potential threat than this one which understandably got the spotlight. It's surely good to be aware of all the processes involved but the probabilities of different events and outcomes should also direct our responses.

acqq 6y ago

The researchers joke that "animals lie", in the sense that animals can have different reactions compared to humans, in spite of the researchers trying as much as possible to get something useful in the experiments. Having said that, I still believe your claim of what can be concluded to be unlikely based on "animal model observation" is false, from what is known up to now. Specifically: https://www.medscape.com/viewarticle/941030?src=soc_tw_201118_mscpedt_news_mdscp_vaccine&faf=1 https://www.medscape.com/viewarticle/941030?src=soc_tw_20111... "In an ideal world, a vaccine would prevent infection entirely and, it follows, also prevent disease and severe disease. But this may be hard to achieve for a respiratory virus vaccine. Animal challenge data suggest that vaccinated animals may still be infected even if they don't experience symptoms. A vaccine that is able to reduce the severity of disease, even if it cannot prevent infection entirely, would obviously still have enormous public health value. Therefore, this is what trials target as their primary aim." I suggest everybody to read carefully the whole article, as it is written by an indisputable expert, and what is presented in the article isn't based only on the animal models but on much broader knowledge. Nobody at this moment should expect that the vaccines guarantee that somebody who is vaccinated won't be able to infect somebody who hasn't received a vaccine. That, for example, means that even if the health workers do get a vaccine they will still have to wear protective equipment.

jfoster 6y ago
Might this also have a silver lining? If the virus is still able to spread, does that mean that it is less likely to face selection pressure to mutate around the vaccines?
- acqq 6y ago
  Contrary to what is often believed, regarding mutations, coronaviruses behave completely differently than flu viruses. The mutation rate among coronaviruses is so slow that it's much more probable that whenever we see some new significant change among them it is due to the recombination, not due to the mutation. Coronaviruses have a specific mechanism of "error correction" in them which lowers the mutation rate, compared to most RNA viruses. The "selection pressures" are also less likely in this case then most would estimate. We as humans are much more "pressured" by this virus in its current form than the virus by anything we'd do. The viruses themselves don't even "need" to come "around" anything, and there are enough unknown viruses in the world which aren't less potential threat than this one which understandably got the spotlight. It's surely good to be aware of all the processes involved but the probabilities of different events and outcomes should also direct our responses.