The propagation of COVID-19 or SARS-CoV-2 has led to a global public health crisis, and many questions remain to be fully elucidated. With early reports identifying several documented cases of COVID-19 reinfections, the uncertainty of the length of immunity after recovering from COVID-19 has been an emerging concern among individuals who have already contracted the novel coronavirus. Although ongoing studies may not fully decipher all of the ambiguities surrounding the pathophysiology of the novel coronavirus, it is imperative to consider that scientific evidence is continually evolving not only to help us further understand the premise of new phenomena, but also to help mitigate any health concerns with new, improving solutions. 

Documenting COVID-19 reinfection is rather complicated. There are several variables that health departments consider in accounting for suspected cases of COVID-19 reinfections. The Center for Disease and Control and Prevention (CDC) have proposed a criteria to help determine if an individual is suspected with reinfection [1]. Their recommended protocol is to analyze genomic data sequences between the first and second instances of infection. Genomic sequencing can indicate if there are different nucleotide variants between two specimens. Additionally, the usage of genomic databases, particularly Nextstrain and GISAID, can help validate whether the variations of the sequences are truly distinctive, as defined by their genomic data references. Thus, investigating these findings will help determine if a patient is infected on two separate occurrences with definitive evidence. 

Currently, recorded cases of COVID-19 reinfection are relatively rare among the 68 million cases worldwide. Tillett et al (2020) documented one case in the U.S. in which a 25-year-old male was previously diagnosed with COVID-19 on April 18, 2020 with a second positive test on June 5, 2020 [2]. Their genomic findings indicate that the patient was infected twice by SARS-CoV-2 with genetically distinct lineages of the novel coronavirus. In other words, the patient was found with two forms of the virus containing different genomic sequences. It was also found that the patient had more severe symptoms with the second infection. Another study describes a case of reinfection in which genomic analysis revealed nucleotide differences in a 142-day interval between the first and second viral infections [3]. In comparison of these two episodes, the patient presented with mild symptoms in the first occurrence of infection whereas he appeared to be asymptomatic in the second occurrence of infection. Further research is needed to determine a clear clinical indicator of whether symptoms are more severe for cases of COVID-19 reinfections. 

It is important to note that reinfections are not uncommon in many respiratory viruses. For example, individuals who recovered from coronaviruses like SARS-CoV-1 and Middle East respiratory syndrome coronavirus (MERS-CoV) were found to have antibodies up to 24-34 months, respectively [4] as opposed to having a permanent form of protection. Thus, natural exposure to respiratory viruses like COVID-19 may not guarantee lifelong immunity, rather it may be temporary. This leads to the ambiguous question of how long immunity lasts for those who have recovered from COVID-19. Currently, it is still uncertain. Several publications have indicated that COVID-19 patients who had mild or no symptoms were found to have low levels of neutralizing antibodies [5-7]. A recent study has also shown COVID-19 IgG antibodies rapidly declining over a period of one to three months [7]. IgG antibodies are the most common type of antibodies found in blood and other fluids that help protect against bacterial and viral infections. Subsequently, declining COVID-19 IgG antibodies may potentially lead to more cases of reinfection as Selvaraj et al (2020) indicate that patients with mild or asymptomatic COVID-19 appear to be more susceptible to reinfection [8]. Nonetheless, more studies are needed to validate these clinical findings. 

The concept ‘herd immunity’ is often suggested in order to successfully mitigate the spread of the novel coronavirus. Herd immunity is only achieved when an infected individual in a given population yields less than one secondary case on average [9]. Achieving herd immunity protects individuals such as babies, elders, and those with a weakened immune system who cannot be vaccinated. Therefore, it is vital to get vaccinated not only to help one’s own immune system develop protection against novel viral and bacterial diseases, but also to protect the aforementioned populations. 

Although occurrences of COVID-19 reinfections have not appeared to be significant so far, there is still an emerging possibility of more reinfection cases arising in the near future with holiday travel around the corner. Thus, natural exposure to COVID-19 may not ensure a long-lasting immunity. Even with an effective vaccine in the upcoming months, all individuals must remain diligent and persistent in following the CDC safety guidelines and protocols to successfully achieve herd immunity and thereby mitigate the spread of the novel coronavirus.

References

[1] Investigative Criteria for Suspected Cases of SARS-CoV-2 Reinfection (ICR) | CDC. (n.d.). Retrieved December 9, 2020, from https://www.cdc.gov/coronavirus/2019-ncov/php/invest-criteria.html

[2] Tillett, R. L., Sevinsky, J. R., Hartley, P. D., Kerwin, H., Crawford, N., Gorzalski, A., Laverdure, C., Verma, S. C., Rossetto, C. C., Jackson, D., Farrell, M. J., Van Hooser, S., & Pandori, M. (2020). Genomic evidence for reinfection with SARS-CoV-2: a case study. The Lancet Infectious Diseases, 0(0). https://doi.org/10.1016/S1473-3099(20)30764-7

[3] To, K. K.-W., Hung, I. F.-N., Ip, J. D., Chu, A. W.-H., Chan, W.-M., Tam, A. R., Fong, C. H.-Y., Yuan, S., Tsoi, H.-W., Ng, A. C.-K., Lee, L. L.-Y., Wan, P., Tso, E. Y.-K., To, W.-K., Tsang, D. N.-C., Chan, K.-H., Huang, J.-D., Kok, K.-H., Cheng, V. C.-C., & Yuen, K.-Y. (2020). Coronavirus Disease 2019 (COVID-19) Re-infection by a Phylogenetically Distinct Severe Acute Respiratory Syndrome Coronavirus 2 Strain Confirmed by Whole Genome Sequencing. Clinical Infectious Diseases. https://doi.org/10.1093/cid/ciaa1275

[4] Yahav, D., Yelin, D., Eckerle, I., Eberhardt, C. S., Wang, J., Cao, B., & Kaiser, L. (2020). Definitions for COVID-19 reinfection, relapse and PCR re-positivity. Clinical Microbiology and Infection : The Official Publication of the European Society of Clinical Microbiology and Infectious Diseases, 0(0). https://doi.org/10.1016/j.cmi.2020.11.028

[5] Havers, F. P., Reed, C., Lim, T., Montgomery, J. M., Klena, J. D., Hall, A. J., Fry, A. M., Cannon, D. L., Chiang, C. F., Gibbons, A., Krapiunaya, I., Morales-Betoulle, M., Roguski, K., Rasheed, M. A. U., Freeman, B., Lester, S., Mills, L., Carroll, D. S., Owen, S. M., … Thornburg, N. J. (2020). Seroprevalence of Antibodies to SARS-CoV-2 in 10 Sites in the United States, March 23-May 12, 2020. JAMA Internal Medicine, 180(12), 1576–1586. https://doi.org/10.1001/jamainternmed.2020.4130

[6] Ibarrondo, F. J., Fulcher, J. A., Goodman-Meza, D., Elliott, J., Hofmann, C., Hausner, M. A., Ferbas, K. G., Tobin, N. H., Aldrovandi, G. M., & Yang, O. O. (2020). Rapid Decay of Anti–SARS-CoV-2 Antibodies in Persons with Mild Covid-19. New England Journal of Medicine, 383(11), 1085–1087. https://doi.org/10.1056/nejmc2025179

[7] Nag, D. S., Chaudhry, R., Mishra, M., Rai, S., & Gupta, M. (2020). A Prospective Study on Rapidly Declining SARS‐CoV‐2 IgG Antibodies Within One to Three Months of Testing IgG Positive: Can It Lead to Potential Reinfections? Cureus, 12(12). https://doi.org/10.7759/cureus.11845

[8] Selvaraj, V., Herman, K., & Dapaah-Afriyie, K. (2020). Severe, Symptomatic Reinfection in a Patient with COVID-19. Rhode Island Medical Journal (2013), 103(10), 24–26. http://www.ncbi.nlm.nih.gov/pubmed/33172223

[9] Fontanet, A., & Cauchemez, S. (2020). COVID-19 herd immunity: where are we? In Nature Reviews Immunology (Vol. 20, Issue 10, pp. 583–584). Nature Research. https://doi.org/10.1038/s41577-020-00451-5