A total of 63.2 million Americans have tested positive for COVID-19 since the start of the pandemic [1]. Global cases have climbed to almost 320 million [2], and this number is likely to be an underestimate, considering that many have restricted access to testing. Now, COVID-19 goes by a number of names: Alpha, Beta, Gamma, Delta. In the midst of yet another wave of yet another variant, one key question is: does a previous infection confer any safety against Omicron, or is the risk of reinfection higher?
Before the emergence of focused epidemiological research on the Omicron variant, the evidence seemed contradictory. On one hand, previous infection demonstrated protective effects against the Delta variant, the COVID strain which drove the previous wave in the U.S. [3]. On the other hand, scientists have been concerned about the number of mutations that characterize the Omicron variant since it was identified [3]. The concern was that these changes might make the virus unique enough from its predecessors that antibodies and other immune defenses against variants like Delta would no longer be able to target the mutated virus.
In order to answer this question, Juliet Pulliam and her colleagues from the South African Centre of Excellence in Epidemiological Modelling and Analysis conducted a study on 2.8 million positive cases over the course of a week [4]. A substantial 35,670 cases were found to be known reinfections, or approximately 1.3 percent of all cases. Notably, the actual percentage of reinfections is likely to be much higher given testing restrictions and asymptomatic infections. This disappointing result suggested that previous infection offered less protection against Omicron as compared to the other variants.
The authors had started their study in January, following the emergence of the Beta variant in South Africa. Toward the end of 2021, new data showed an unexpected trend: While first infection rates were declining, reinfection rates were climbing in a way that had not yet been seen during the pandemic. This was followed by an overall increase in infection rates: the beginning of the Omicron wave.
Now that more data is available on the Omicron variant, scientists estimate that previous infection only confers half the amount of protection against the new version of the virus as the Delta variant.3 Not only is this finding disappointing for the millions who have already been infected throughout the globe, but it also suggests that countries with high vaccination rates will still be affected by Omicron, as has been the case in the U.S. However, more large-scale studies will be needed to accurately determine the level of protection vaccines confer against Omicron.
Though these findings come as a disappointment for those hoping to see the end of the pandemic, there may be a silver lining when it comes to the Omicron variant. Studies have suggested that, though it drives more reinfection, Omicron is less pathogenic when compared to previous variants [5]. Scientists and healthcare workers alike remain hopeful that this translates to reduced morbidity and mortality throughout the latest wave of infections, and some have also expressed hope that SARS-CoV-2 will eventually morph into a widespread but mild infection like the common cold.
References
1 Coronavirus in the U.S.: Latest Map and Case Count. (2020, March 03). Retrieved from https://www.nytimes.com/interactive/2021/us/covid-cases.html
2 Coronavirus Cases. (2021). Retrieved from https://www.worldometers.info/coronavirus/
3 COVID-19 reinfection study from South Africa yields ominous data about Omicron. (2021, December 3). Retrieved from https://www.science.org/content/article/covid-19-reinfection-study-south-africa-yields-ominous-data-about-omicron
4 Pulliam, J. R., Schalkwyk, C. V., Govender, N., Gottberg, A. V., Cohen, C., Groome, M. J., . . . Moultrie, H. (2021). Increased risk of SARS-CoV-2 reinfection associated with emergence of the Omicron variant in South Africa. doi:10.1101/2021.11.11.21266068
5 Mcmahan, K., Giffin, V., Tostanoski, L. H., Chung, B., Siamatu, M., Suthar, M. S., . . . Barouch, D. H. (2022). Reduced Pathogenicity of the SARS-CoV-2 Omicron Variant in Hamsters. doi:10.1101/2022.01.02.474743