06-22-2020, 07:49 AM
A few quick comments:
Global confirmed infections is a fraction of the total number of patients who have been infected with the virus. Even in countries that are testing extensively, serology suggests that positives tests account for roughly 1/10th the number of total people exposed (based on serology studies in Spain and New York). The testing is probably worse in the developing world, as you surely can intuit from Mexico's 50% positivity rate. So, we are likely over 100 million people exposed to the virus worldwide, and an IFR close to .5. Still there is a long way to go until the world reaches herd immunity.
Second, antibodies are not the sina qua non of immunity. It is not yet clear whether "some people do not develop enough evidence to fight the infection". Although some patients do not develop detectable neutralizing antibodies, it is not yet clear that these patients are at risk for re-infection. The body has a lot of different ways to fight infection, including virus-fighting T cells, and memory B cells, which are capable of ramping up antibody production if the virus is detected again. Evidence of loss of antibodies is not surprising; this has been seen with other coronaviridae. While we have seen reports of patients testing positive after testing negative, I haven't seen any true reports of re-infection (documented symptomatic infection, recovery with negative PCR testing, followed by a subsequent symptomatic re-infection).
That being said, I would not be surprised if there is waning immunity, which is not that unusual for respiratory viruses (for example influenza). The upshot is that re-infection, if/when it happens, tends to result in a less severe disease. So, we might see patients infected a first time who develop severe COVID-19 pneumonia, followed some time later (maybe a year) with an infection resulting in a moderate symptomatic or disease. While there is a reasonable concern about how long the immunity of a vaccine will last, this may result in the need to re-vaccinate yearly (at least until a long-lasting vaccine is developed). While every disease is unique, I don't think SARS-CoV 2 is all that much weirder than other viruses out there. Most specifiically, it looks a lot sort of like a version in between the endemic coronaviridae (which cause cold-like symptoms) and SARS and MERS, which have a higher mortality.
BC
Global confirmed infections is a fraction of the total number of patients who have been infected with the virus. Even in countries that are testing extensively, serology suggests that positives tests account for roughly 1/10th the number of total people exposed (based on serology studies in Spain and New York). The testing is probably worse in the developing world, as you surely can intuit from Mexico's 50% positivity rate. So, we are likely over 100 million people exposed to the virus worldwide, and an IFR close to .5. Still there is a long way to go until the world reaches herd immunity.
Second, antibodies are not the sina qua non of immunity. It is not yet clear whether "some people do not develop enough evidence to fight the infection". Although some patients do not develop detectable neutralizing antibodies, it is not yet clear that these patients are at risk for re-infection. The body has a lot of different ways to fight infection, including virus-fighting T cells, and memory B cells, which are capable of ramping up antibody production if the virus is detected again. Evidence of loss of antibodies is not surprising; this has been seen with other coronaviridae. While we have seen reports of patients testing positive after testing negative, I haven't seen any true reports of re-infection (documented symptomatic infection, recovery with negative PCR testing, followed by a subsequent symptomatic re-infection).
That being said, I would not be surprised if there is waning immunity, which is not that unusual for respiratory viruses (for example influenza). The upshot is that re-infection, if/when it happens, tends to result in a less severe disease. So, we might see patients infected a first time who develop severe COVID-19 pneumonia, followed some time later (maybe a year) with an infection resulting in a moderate symptomatic or disease. While there is a reasonable concern about how long the immunity of a vaccine will last, this may result in the need to re-vaccinate yearly (at least until a long-lasting vaccine is developed). While every disease is unique, I don't think SARS-CoV 2 is all that much weirder than other viruses out there. Most specifiically, it looks a lot sort of like a version in between the endemic coronaviridae (which cause cold-like symptoms) and SARS and MERS, which have a higher mortality.
BC