Re-Infection Related Questions

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Nuha Al-Howthi, MD[2]Gurmandeep Singh Sandhu,M.B.B.S.[3] Aisha Adigun, B.Sc., M.D.[4]

Re-Infection Related Questions

Do patients become immune after recovering from COVID-19?

  • Currently, there is no evidence to suggest that individuals who have recovered from COVID-19 and have antibodies present in their blood are immune or protected from reinfection.[1]
  • The world's first documented re-infection case was recorded on August 15, 2020, when a Hong Kong man returning from international travel re-tested positive four, and a half months after his initial infection[2]. The patient was reported to have tested positive to a strain that was different from his prior infection[2].

Is re-infection worse than the initial infection?

  • There is currently no evidence to show that re-infection is worse than the initial infection.

Will a re-infected person show the same symptoms as the initial infection?

  • Most likely a reinfected individual will present with similar symptoms as the initial infection.

Are clinically recovered persons infectious to others if they test persistently or recurrently positive for SARS-COV-2 RNA?

  • Whether the presence of detectable but low concentrations of viral RNA after clinical recovery represents the presence of the potentially infectious virus is unknown.
    • Based on experience with other viruses, it is unlikely that such persons pose an infectious risk to others. However, whether this is true for SARS-CoV-2 infection has not been definitively established.
    • Typically, after the onset of illness, the detectable viral burden declines. After a week or more, anti-SARS-CoV-2 immunoglobulin becomes detectable, and antibody titers rise. Some of these antibodies may prevent the virus from infecting cells in cell culture. The decline in viral burden is associated with decreased ability to isolate the live virus.
    • Efforts to isolate live virus from upper respiratory tract specimens have been unsuccessful when specimens are collected more than 10 days after illness onset.
  • Persons who have tested persistently or recurrently positive for SARS-CoV-2 RNA have shown stable or improving signs of illness. When viral isolation in tissue culture has been attempted in such persons in South Korea and the United States, live viruses were not isolated.
  • In addition, there is no evidence that clinically recovered persons with persistent or recurrent detection of viral RNA have transmitted COVID-19 to others.
  • Despite encouraging observations to date, it’s not possible to conclude that persons with persistent or recurrent detection of SARS-CoV-2 RNA are no longer infectious.
  • There is no firm evidence yet that the antibodies that develop in response to infection are protective. If these antibodies are protective, it’s not known what antibody titers are associated with protection from reinfection.

Based on these data and experience with other viral infections, most persons recovered from COVID-19 who test persistently or recurrently positive by RT-PCR are likely no longer infectious. Additionally, the magnitude and persistence of the immune response following recovery may vary among individuals, with factors such as age potentially influencing protection.

  • Based on limited available data, determinations must be made on a case-by-case basis as to whether recovered persons with persistently detectable SARS-CoV-2 RNA are potentially infectious to others and should continue to be in-home isolation and excluded from work, school, or other group settings. Such determinations are typically made in consultation with infectious disease specialists and public health officials, after reviewing available information (e.g., medical history, time from an initial positive test, RT-PCR Ct values, and presence of COVID-19 signs or symptoms).[3]

What further evidence is needed to be reassured that persistent or recurrent shedding of SARS-COV-2 RNA after recovery does not represent the presence of infectious virus?

  • Prospectively collecting serial respiratory samples and attempting to isolate the live virus in tissue culture from multiple persons testing positive by RT-PCR following illness recovery is generally required. If repeated attempts to recover replication-competent virus in culture from such serial samples are unsuccessful that is considered sufficient evidence that infectious virus is absent, and that persons continuing to test positive do not pose an infectious risk to other people.[3]

====If the infected person has clinically recovered using the symptom based strategy, do they need a test to show that they are not infectious?[3]

  • No. Symptom based strategy is intended to replace the repeat testing.

What do we know the detection of SARS-COV-2 RNA after clinical recovery of COVID-19?=

  • Many recovered persons do not have detectable SARS-CoV-2 RNA in upper respiratory tract specimens. In others, viral RNA can be persistently detected by RT-PCR in respiratory tract samples after clinical recovery.
  • In some persons, after testing negative by RT-PCR in two consecutive samples, later samples can test positive again. Whether persistent or recurrent, these repeated detections of viral RNA consistently are associated with higher cycle threshold (Ct) values (i.e., fewer RNA copies) than were found in earlier RT-PCR results in samples collected shortly or and during clinical illness.
  • Studies that have looked at how long SARS-CoV-2 RNA can be detected in adults have demonstrated that in some persons it can be detected for weeks.[3]

Can cycle threshold values be used to asses when person is no longer infectious?[3]

  • No. Although attempts to culture virus from upper respiratory specimens have been largely unsuccessful when Ct values are in high but detectable ranges, Ct values are not a quantitative measure of viral burden. In addition, Ct values are not standardized by RT-PCR platform nor have they been approved by FDA for use in clinical management. CDC does not endorse or recommend use of Ct values to assess when a person is no longer infectious. However, serial Ct values may be useful in the context of the entire body of information available when assessing recovery and resolution of infection.

If the person has recovered clinically, should the person continue to wear mask in public?[3]

  • Yes. It is recommended that all persons, with a few exceptions, wear cloth face coverings in public. The primary purpose of cloth face coverings is to limit transmission of SARS-CoV-2 from infected persons who may be infectious but do not have clinical symptoms of illness or may have early or mild symptoms that they do not recognize. Cloth face coverings may provide reassurance to others in public settings and be a reminder of the need to maintain social distancing. However, cloth face coverings are not personal protective equipment (PPE) and should not be used instead of a respirator or a face mask to protect a healthcare worker.
  • Cloth face coverings should not be placed on young children under age 2, anyone who has trouble breathing, or anyone who is unconscious, incapacitated, or otherwise unable to remove the mask without assistance.

If an infected patient person has clinically recovered and is later identified as a contact of a new case, do they need to be quarantined?[3]

  • Withing 3 months of recovery: A person who has clinically recovered from COVID-19 and then is identified as a contact of a new case does not need to be quarantined or retested for SARS-CoV-2.
  • After 3 months: If a person is identified as a contact of a new case, they should follow quarantine recommendations for contacts.


  1. ""Immunity passports" in the context of COVID-19".
  2. 2.0 2.1 "Hong Kong researchers report first documented coronavirus re-infection - Reuters".
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 "Clinical Questions about COVID-19: Questions and Answers | CDC".