text: We only have a few dozen confirmed cases in the medical literature of what looks like reinfection with Covid-19. (20:10)
  Sarah points out that research on these common cold coronaviruses shows immunity doesn’t last that long- maybe as little as a year.
  Sarah outlines several studies that measured infection rates and discusses the results in terms of developing immunity.
  Sarah explains that many test subjects showed partial immunity. This means their bodies had enough familiarity with the virus to fight it with less symptoms.
  Sarah explains that having partial immunity to Covid-19 could potentially result in more asymptomatic reinfections.
  About 40% of spread happening right now is from a combination of asymptomatic and pre-symptomatic people.
  This means that even if you’re immune enough that you might not get a symptomatic infection upon a subsequent exposure, you may have a higher likelihood of being an asymptomatic carrier.
  Sarah tells us that SARS from the 2002 and 2003 epidemic is about 80% the same as the Covid-19 virus in terms of gnome sequence.
  Sarah explains that all this data tells us that reinfection is something that we may need to be concerned about.
  What’s happened in these few dozen cases of possible Covid-19 reinfection is that people tested positive and were sent home. They recovered and later tested negative. Then, months later, they once more test positive for Covid-19.
  Some are similarly sick as the first time, some are sicker the second time, and others are asymptomatic.
  Sarah claims that of the researchers studying these cases, nobody is convinced that it’s true reinfection.
  A more likely explanation for what is going on with these cases is that it’s actually viral reactivation.
  This means that these people are long-haulers who had a latent period, combined with testing limitations and failures.
  Sarah explains this as the immune system almost beat it, but didn’t neutralize it fully, and pulled back fighting too soon.
  There’s a really wide range in how long people have measurable virus in their systems, and they may not be infectious the entire time.
  Sarah explains that there’s a lot that we still don’t know about the Covid-19 virus and its ability to hide out in our bodies long-term.
  Data has shown viral shedding in some people lasting as long as eighty-three days out from the first day of symptoms.
  Some of the recovered/discharged patients showed a positive viral RNA burden for as long as 10 to 27 days after the discharge (Korber et al., 2020; Ye et al., 2020)
  Although the median viral shedding duration was 20 days, in some cases, it was observed for 37 days (Zhou et al., 2020).
  The prolonged SARS-CoV-2 RNA shedding occurred with a median duration of 53 days and a maximum of 83 days (Li, Wang, et al., 2020).
  In addition to this prolonged carriage of SARS-CoV-2, some patients who had recovered from COVID-19 demonstrated recurrence of SARS-CoV-2 (Xiao et al., 2020; Ye et al., 2020; Yuan et al., 2020).
  In one study, as much as 9.1% of the discharged COVID-19 patients were shown to be presented with the SARS-CoV-2 reactivation (Ye et al., 2020).
  Another study revealed that 14.5% of discharged COVID-19 patients with negative (polymerase chain reaction) PCR, had a later positive reverse transcription PCR (Yuan et al., 2020).
  Still another study indicated that the number of such recurring patients can be as high as 21.4% (Xiao et al., 2020).
  Another explanation is genetic mutations causing new strains. Sarah explains this is not likely. While there variants, they are not different enough to be considered a new strain.
  Sarah sums up that the most likely explanation for the resurgence of symptoms is due to the virus’s ability to hide inside our bodies. (36:03)
  One of the implications of this is that we could have more lasting immunity from a vaccine than natural infection.