first published: 24.11.2020
Context: In scientific literature as well as in common news media, there are scattered reports of SARS-CoV-2 ‘reinfection’, mostly experiencing asymptomatic or mild symptoms during the first infection. Meanwhile, there are also reports accumulating for people with prolonged SARS-CoV-2 symptoms, some reporting up to several months since the first diagnosis, and sometimes termed as ‘long-COVID’. Both are clinical manifestations following the SARS-CoV-2 infection and is not well understood at present, partly because the immunology of asymptomatic individuals or symptomatic individuals with mild symptoms (no hospitalization required) is not a priority at the moment.
Observations and Hypothesis: Initial studies show a wide range of SARS-CoV-2 ‘viral-shedding‘ in infected individuals, from a few days to up to several weeks. Although the mechanistic details are unclear, the fact remains that certain proportion of population (probably a small minority) is experiencing a longer period of ‘viral shedding’ (a prolonged period of viral clearance). In principle, such individuals pose a higher risk for themselves (in case of mild- to medium-symptoms, would experience ‘long-COVID’) and others (in case of asymptomatic cases, may infect others without knowing it). In effect, it would mean that a ‘small’ fraction of recovered cases, with or without symptoms (mild-disease), who are able to socialize after 10-14 days of ‘quarantine-period’ BUT without a confirmatory SARS-CoV-2 negative PCR test, has the hallmarks of prolongling the pandemic.
Coming back to the possibility of a ‘reinfection’, there are probably two major possibilities. First, it is not a ‘true reinfection’ and rather a ‘recurrence or reactivation’ of the primary infection following a waning immune respose and the virus can propagate again. It may be argued that the antibodies are not sufficient to avoid a ‘recurrence or reactivation’ of the infection, it should be appreciated and noted that even if a suboptimal response, antibodies protect against developing severe forms of the COVID-19 disease in these individuals (for severe COVID-19, see section below). The second possibility could be a ‘true reinfection’, which would clinically mean that an another strain of the SARS-CoV-2 infecting an individual for a second time, which could not be recognized by the immune response developed during the first infection. The second possibility although has a very small probability, if true, would have large implications on vaccine development and ‘herd-immunity’.
It may also be important to mention that in case of severe COVID-19 disease, comorbidities (like cardiovascular disease, diabetes and obesity, are most common), immunocompromised or immunosuppressed individuals, age (old versus young), gender (male and female) and genetic factors (like blood groups) also play a role, further complicating a simple and universal solution like a ‘single type’ of vaccine for everyone.
In summary, the individual immune responses during SARS-CoV-2 infection or COVID-19 desease remains varied and largely unknown, and probably the acquired immunity following vaccination would also vary a lot amongst individuals, and consequently further caution in terms of re-opening activities with large gatherings, maintaining interpersonal distance, hygiene measures and post-recovery PCR tests are warranted.