> Will it reinfect persons who has already been infected?
At present time, a number of studies show that reinfection in people with naturally acquired immunity is relatively rare (see supporting excerpts below).
That said, the delta variant (and most other variants of concern) have mutations that confer partial immune escape . We can expect that such variants will pose an increasing risk to both the vaccinated & naturally immune. [5][6][7]
The virus can mutate faster than the scientific literature can establish consensus - I suppose we'll be facing a degree of uncertainly for a while to come.
> "A previous history of SARS-CoV-2 infection was associated with an 84% lower risk of infection, with median protective effect observed 7 months following primary infection. This study shows that previous infection with SARS-CoV-2 induces effective immunity to future infections in most individuals." [1]
> "Reinfection is rare in the young and international population of Qatar. Natural infection appears to elicit strong protection against reinfection with an efficacy ~95% for at least seven months." [2]
> "To our knowledge, this is the first systematic review to synthesise the evidence on the risk of SARS‐CoV‐2 reinfection over time. [...] Reinfection was an uncommon event (absolute rate 0%–1.1%), with no study reporting an increase in the risk of reinfection over time. [...] These data suggest that naturally acquired SARS‐CoV‐2 immunity does not wane for at least 10 months post‐infection. However, the applicability of these studies to new variants or to vaccine‐induced immunity remains uncertain." [3]
> "Cumulative incidence of COVID-19 was examined among 52238 employees in an American healthcare system. COVID-19 did not occur in anyone over the five months of the study among 2579 individuals previously infected with COVID-19, including 1359 who did not take the vaccine. [...] Individuals who have had SARS-CoV-2 infection are unlikely to benefit from COVID-19 vaccination, and vaccines can be safely prioritized to those who have not been infected before." [4]
[1] SARS-CoV-2 infection rates of antibody-positive compared with antibody-negative health-care workers in England: a large, multicentre, prospective cohort study (SIREN)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8040523/
At present time, a number of studies show that reinfection in people with naturally acquired immunity is relatively rare (see supporting excerpts below).
That said, the delta variant (and most other variants of concern) have mutations that confer partial immune escape . We can expect that such variants will pose an increasing risk to both the vaccinated & naturally immune. [5][6][7]
The virus can mutate faster than the scientific literature can establish consensus - I suppose we'll be facing a degree of uncertainly for a while to come.
> "A previous history of SARS-CoV-2 infection was associated with an 84% lower risk of infection, with median protective effect observed 7 months following primary infection. This study shows that previous infection with SARS-CoV-2 induces effective immunity to future infections in most individuals." [1]
> "Reinfection is rare in the young and international population of Qatar. Natural infection appears to elicit strong protection against reinfection with an efficacy ~95% for at least seven months." [2]
> "To our knowledge, this is the first systematic review to synthesise the evidence on the risk of SARS‐CoV‐2 reinfection over time. [...] Reinfection was an uncommon event (absolute rate 0%–1.1%), with no study reporting an increase in the risk of reinfection over time. [...] These data suggest that naturally acquired SARS‐CoV‐2 immunity does not wane for at least 10 months post‐infection. However, the applicability of these studies to new variants or to vaccine‐induced immunity remains uncertain." [3]
> "Cumulative incidence of COVID-19 was examined among 52238 employees in an American healthcare system. COVID-19 did not occur in anyone over the five months of the study among 2579 individuals previously infected with COVID-19, including 1359 who did not take the vaccine. [...] Individuals who have had SARS-CoV-2 infection are unlikely to benefit from COVID-19 vaccination, and vaccines can be safely prioritized to those who have not been infected before." [4]
[1] SARS-CoV-2 infection rates of antibody-positive compared with antibody-negative health-care workers in England: a large, multicentre, prospective cohort study (SIREN) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8040523/
[2] SARS-CoV-2 antibody-positivity protects against reinfection for at least seven months with 95% efficacy https://pubmed.ncbi.nlm.nih.gov/33937733/
[3] Quantifying the risk of SARS‐CoV‐2 reinfection over time https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8209951/
[4] Necessity of COVID-19 vaccination in previously infected individuals https://www.medrxiv.org/content/10.1101/2021.06.01.21258176v...
[5] SARS-CoV-2 immune evasion by the B.1.427/B.1.429 variant of concern https://science.sciencemag.org/content/early/2021/06/30/scie...
[6] mRNA vaccine-elicited antibodies to SARS-CoV-2 and circulating variants https://www.nature.com/articles/s41586-021-03324-6
[7] Reduced sensitivity of SARS-CoV-2 variant Delta to antibody neutralization https://www.nature.com/articles/s41586-021-03777-9