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NBCNews article Feb 7, 2021
Quote:[reinfections] are different from instances of so-called long-haul Covid-19, in which the original infection triggers debilitating symptoms that linger for months and viral particles can continue to be detected. Reinfection occurs when a person is infected with Covid-19, clears that strain and is infected again with a different strain, raising concerns about sustained immunity from the disease. Such reinfections occur regularly with four other coronaviruses that circulate among humans, causing common colds.
Quote:Early studies suggested immunity would be short-lived, only a few months, while more recent research finds that certain antibodies and memory cells may persist in Covid-infected patients longer than eight months.

CDC page on COVID reinfection (as typical, says nothing).

NYPost article Feb 1, 2021 reporting on a as-yet-unreviewed Jan 29 paper.
From the Jan 29. report:
Quote:The study population comprised 3,249 predominantly male, 18-20-year-old Marine recruits. Upon arrival at a Marine-supervised two-week quarantine, participants were assessed for baseline SARS-CoV-2 IgG seropositivity,

SARS-CoV-2 infection was assessed by PCR at initiation, middle and end of the quarantine. After appropriate exclusions, including participants with a positive PCR during quarantine, we performed three biweekly PCR tests in both seropositive and in seronegative groups once recruits left quarantine and entered basic training and baseline neutralizing antibody titers on all subsequently infected seropositive and selected seropositive uninfected participants.

Among 189 seropositive participants, 19 (10.1%) had at least one positive PCR test for SARS-CoV-2 during the six-week follow-up (1.1 cases per person-year). In contrast, 1,079 (48.0%) of the 2,247 seronegative participants tested positive (6.2 cases per person-year).

Interpretation Seropositive young adults had about one-fifth the risk of subsequent infection compared with seronegative individuals. Although antibodies induced by initial infection are largely protective, they do not guarantee effective SARS-CoV-2 neutralization activity or immunity against subsequent infection. 
(The interpretation is what is most uncertain in an unreviewed paper.)

To me, the big numbers are the 6.2 cases per person-year for the people never infected and the 1.1 cases per person year for the previously infected.  If those hold up, then in the situation these people are in, they will get an infection every year.  (That depends partly on the frequency of exposure, which depends on the number of people with active infections.  So, that 1.1 should drop as we approach herd immunity.)

IMO, a problem is the difference between PROVABLE reinfection and probable  reinfection.  Provable requires a genome sequence of the first infection and of the second infection and that they be different. Probable reinfection is a positive test, followed by no symptoms and a negative test, followed by a subsequent positive test.  The low numbers you hear are provable reinfections.  The Jan 29 study shows probable reinfections.
I agree . . . I am very interested in statistics around "probable" reinfections.
The NBC news article brings up a good point overall. It's time we get a handle on reinfection and/or long haul. The CDC page says nothing because very little is actually known.

M_T's first quote makes claims about the difference between reinfection and long haul. People actually span the whole spectrum. Some get better then they develop long haul symptoms. Some never have symptoms go away. Some test negative, some never test negative. It's a mess. That distinction between reinfection and long haul is based on common sense and similarity to other corona viruses. This is essentially all we have to go on.  What they say is probably true, but not known to be true. COVID breaks a lot of rules. It may be years until we really know what's happening.

One mystery is the detection of viral particles for a long period of time. This happens in the tissues of some long haul people and on surfaces. It drives virologists nuts. The viral particles were believed to be unstable before COVID. Many stated that the long haulers with viral particles must have replicating virus in the body because the particles don't last in the body. That's true for other corona viruses but it always comes back to the fact that COVID differs in important ways. This mystery may be involved with the reninfection and/or long haul mystery. 

I do not know of a corona virus hiding from the immune system and reinfecting, but other viruses do hide in the body and avoid the immune system only to reinfect (having nothing to do with mutations). Herpes is a very common example, so is shingles (varicella-zoster or chickenpox), even parasites like the one that causes malaria can do this. 

From the same NBCNews article:

Quote:Because the coronavirus, like other viruses, regularly mutates as it multiplies and spreads through a community, a new infection would bear a different genetic fingerprint.

The first part of the sentence is true: COVID mutates. The last part, that a reinfection must be a mutated version,  is common sense but unproven. Parts of the immune system are known to fade after infection with the coronavirus. (The vaccines do much better in this aspect). It is possible that essentially the same virus reinfects. We just don't know. Again, the point of the article is correct, we should sequence everything so we can begin to understand what is actually happening. Am I wrong, is there some unreferenced proof that you need to prove two different variants for it to be a mutation?

I can not criticize the quote from the NYPost because they are stating observations, not broad common sense conclusions. But I will caution that testing for IgG seropositivity is new and there is question whether or not seropositivity means a prior COVID infection or perhaps a prior coronavirus infection. Perhaps it's a mix of both. Perhaps most of the seropositive cases were a plain old corona virus and some were COVID but non of the COVID ones got reinfected. 

With so much effort, science, and investigation going on it's really astonishing how much has not yet been pinned down as certain.

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