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I keep hearing people are recovering from COVID-19 virus. Is there any chance that same person can become infected with COVID-19 for a second time?

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Short answer: Although there are some reports on this, it is pretty unlikely. It is more likely that patients where released too early from hospital, developed further symptoms later on and got worse, was re-hospitalized, tested again for SARS-CoV2, which was positive and counted as re-infected.

Another possibility is that a false negative test happened, when people got re-tested later the test was positive again and the patient was counted as re-infected. Given the rising number of cases worldwide this should become evident pretty soon, if this is a real problem and not an artefact. For the moment, I don't think there is enough evidence for the re-infection of the same patient in such a short time period. If this holds, future will tell.

Long answer: There is now an experimental paper, which infected rhesus macaques with SARS-CoV2, tested if the infection was similar to humans happening in the upper airways (which it was), and re-infected the animals after 28 days with a really high dose of virus (which is much higher than what comes around in our environment), with none of the macaques getting re-infected or showing pathological signs of the infection. See reference 1 for details. This article has its limitations with small sample size and the general questions if the chosen animal model is really comparable with human.

Additionally it looks very much like that patients who are recovering don't shed infectious virus anymore. The PCR test however does not discriminate between infectious virus and plain virus RNA, so it is most like much longer positive than people are infectious. They also show the rapid appearance of specific antibodies, which would at least temporarily protect against a re-infection. See reference 2 for a nice summary and reference 3 for the original article.

References

  1. Reinfection could notoccur in SARS-CoV-2 infected rhesus macaques
  2. People ‘shed’ high levels of coronavirus, study finds, but most are likely not infectious after recovery begins
  3. Clinical presentation and virological assessment of hospitalized cases of coronavirus disease 2019 in a travel-associated transmission cluster

Edit (24.11.2021):

Being 1,5 years further into this pandemic there are clear signs now that reinfections are possible, although it was first thought it should not be a concern. There are a few reasons for this, mainly the occurence of new, much more infectious viral strains (Delta variant), waning of the immune respone (in vaccinated and also people who got infected), weak immune responses at all (reinfection probably occurs in connection with the Delta variant). Following reference 4 (thanks to @bob1 for the hint) below, it seems that reinfections are less severe than primary infections.

For more information please have a look into the additional references below. This shows very well the problem with an unknown pathogen and the rapidly ongoing research on it.

Added references (24.11.2021):

  1. Risk of SARS-CoV-2 reinfection after natural infection
  2. The durability of immunity against reinfection by SARS-CoV-2: a comparative evolutionary study
  3. Prospects for durable immune control of SARS-CoV-2 and prevention of reinfection
  4. Severity of SARS-CoV-2 Reinfections as Compared with Primary Infections
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  • $\begingroup$ Update: Coronavirus reinfection has been reported in India for the first time. See this news: google.com/amp/s/www.timesnownews.com/amp/india/article/… $\endgroup$
    – Nilay Ghosh
    Sep 7, 2020 at 5:01
  • $\begingroup$ And in US: indianexpress.com/article/coronavirus/… $\endgroup$
    – Nilay Ghosh
    Sep 7, 2020 at 5:03
  • $\begingroup$ @NilayGhosh I have read newspaper articles about this as well, but I would like to see a scientific paper first, before I update this answer. I am following this :-) $\endgroup$
    – Chris ♦
    Sep 7, 2020 at 6:23
  • $\begingroup$ Good answer. There's an interesting paper in NEJM today on severity of infection in re-infected patients, that might be worth including. $\endgroup$
    – bob1
    Nov 24, 2021 at 23:42
  • $\begingroup$ @bob1 Thanks for the hint, this looks indeed interesting. I will include this as well. $\endgroup$
    – Chris ♦
    Nov 25, 2021 at 6:33

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