A FaceBook friend asked me what is the chance of reinfection if you recovered from COVID-19. A quick search revealed many studies that show a low risk of infection. I answered her and made this article.
The studies are listed in no particular order. Emphasis added.
1. Re-infection Rates among Patients who Previously Tested Positive for COVID-19: a Retrospective Cohort Study
Clinical Infectious Diseases for November 2021. Large study with 150,325 patients who recovered from COVID from March 2020 to August 2020. The study period was up to February 2021. [1]
Protection offered from prior infection was 81.8% and against symptomatic infection was 84.5% (95% CI, 77.9-89.1). This protection increased over time.
Prior infection in patients with COVID-19 was highly protective against reinfection and symptomatic disease. This protection increased over time, suggesting that viral shedding or ongoing immune response may persist beyond 90 days and may not represent true reinfection.
As vaccine supply is limited, patients with known history of COVID-19 could delay early vaccination to allow for the most vulnerable to access the vaccine and slow transmission.
The International Journal of Infectious Diseases. 508,521 study population. [2]
Results: The protective effect from prior infection was 80.3% for those aged 20–59 years and 67.4% for those aged ≥60 years.
At 30-day time periods through 270 days (9 months), protection was estimated to be >75% for those aged 20–59 years and >65% for those aged ≥60 years.
3. Protective immunity after recovery from SARS-CoV-2 infection
Lancet Infectious Diseases. November 2021. [3]
Results: (We) found that the risk of repeat SARS-CoV-2 infection decreased by 80·5–100% among those who had had COVID-19 previously.
The reported studies were large and conducted throughout the world.
Another laboratory-based study that analysed the test results of 9119 people with previous COVID-19 from Dec 1, 2019, to Nov 13, 2020, found that only 0·7% became reinfected.
4. A Systematic Review of the Protective Effect of Prior SARS-CoV-2 Infection on Repeat Infection
Evaluation & the Health Professions. [4]
Ten population studies that included 9,930,470 individuals from all over the world were reviewed systematically.
The weighted average risk reduction against reinfection was 90.4%.
Protection against SARS-CoV-2 reinfection was observed for up to 10 months.
The protective effect of prior SARS-CoV-2 infection on re-infection is high and similar to the protective effect of vaccination.
The authors’ can only conclude that the protective effect is ten months because that is the duration of the study.
5. Necessity of COVID-19 vaccination in previously infected individuals.
A preprint study from the Departments of Infectious Diseases, Cleveland Clinic. [5] involving 52,238 employees of the Cleveland Clinic Health System.
- 1,359 previously infected who remain unvaccinated compared with
- 20804 (42%) of 49659 not previously infected.
Result: The cases of COVID-19 remained almost zero among
- previously infected unvaccinated subjects.
- previously infected subjects who were vaccinated, and
- previously uninfected subjects who were vaccinated
In comparison, there was a steady increase in COVID-19 among previously uninfected subjects who remained unvaccinated. That’s the reason for the title.
May I suggest early treatment of COVID-19 of the health care workers of Clevland Clinic?
6. Reinfection with SARS-CoV-2 in Patients Undergoing Serial Laboratory Testing
Clinical Infectious Diseases. April 2021.
We analyzed 9,119 patients with SARS-CoV-2 infection who received serial tests in a total of 62 healthcare facilities in the United States between December 1, 2019, to November 13, 2020
Results: Re-infection was identified in 0.7% during follow-up of 9,119 patients with SARS-CoV-2 infection.
There was a significantly lower rate of pneumonia, heart failure, and acute kidney injury observed with re-infection compared with primary infection among the 63 patients with re-infection
There were two deaths (3.2%) associated with re-infection.
Asthma doubles the risk (odds ratio 1.9), and nicotine dependence/tobacco use increases the risk almost three times (OR 2.7) of reinfection.
7. SARS-CoV-2 infection rates of antibody-positive compared with antibody-negative healthcare workers in England: (SIREN)
April 2021. A large, multicentre, prospective cohort study was done, with 25,661 participants recruited from publicly funded hospitals in all regions of England. [6]
Interpretation of results: A previous history of SARS-CoV-2 infection was associated with an 84% lower risk of infection, with a 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.
8. COVID-19 reinfection in healthcare workers: A case series
The Journal of Infection. 677 subjects [7]
Only thirteen patients (only 1.9%) were diagnosed with reinfection out of 677. Symptoms were mild in all the subjects. Nobody was hospitalized
9. Assessment of SARS-CoV-2 Reinfection 1 Year After Primary Infection in a Population in Lombardy, Italy
Journal of the American Medical Association. October 2021. [9]
5 reinfections (0.31%) were confirmed in the cohort of 1579 positive patients. Only 1 was hospitalized, and 4 patients had a close relationship (2 patients work in hospitals, 1 patient underwent transfusions every week, and 1 patient retired in a nursing home)
10. SARS-CoV-2 reinfection risk in Austria
European Journal of Clinical Investigation. April 2021. [10]
Results: We recorded 40 tentative re-infections in 14,840 COVID-19 survivors of the first wave (0.27%) and 253,581 infections in 8,885, 640 individuals of the remaining general population (2.85%) translating into an odds ratio of 0.09 .
Conclusions: We observed a relatively low re-infection rate of SARS-CoV-2 in Austria.
Protection against SARS-CoV-2 after natural infection is comparable with the highest available estimates on vaccine efficacies.
The odds ratio of 0.09 means that previous COVID-19 reduced the risk of reinfection by 91%.
What is the duration of vaccine protection?
Consider that the duration of the studies limits the conclusions. Two studies above mentioned that the protection lasts for at least 8 to ten months (2,4).
In comparison, studies have shown that vaccine protection only lasts for six months at the most.
Neutralizing antibodies from Pfizer vaccination lasts for only six months. Durable Immunity from Pfizer COVID-19 Vaccine Lasts only Six Months.
Pfizer’s protection and AstraZeneca’s protection against the Delta variant infection were only 14% and 24%, respectively. – How effective are the Pfizer and AstraZeneca vaccines against COVID-19 household spread?
A study about the effectiveness of the Moderna vaccine used surrogate end-points (antibody levels against the spike protein) instead of clinical outcomes to demonstrate that their vaccine is effective. However, there were no other studies to confirm their results which is the standard research practice. That is why – The Durability Study of the Moderna COVID-19 Vaccine is Strange and Unusual
Measurement of surrogate end-points like antibody levels instead of actual clinical outcomes is a technique that vaccine makers do to show that their product is effective. Note that all the reinfection studies measured clinical outcomes.
Lastly, research from a Harvard faculty showed that vaccination does not affect the number of COVID-19 cases. –Study: Vaccination Does Not Affect the Number of COVID-19 Cases
Take Away Message
The protection provided by the previous infection of COVID-19 is the same as vaccination. Natural immunity is longer than vaccine induced-immunity.
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Related to Natural Immunity
- High Anti-SARS-CoV-2 Antibodies Among the Unvaccinated in Bangui, Central African Republic
- Protective Antibodies against SARS-CoV-2 are the same in Convalescent and Vaccinated
- Asymptomatic or mild symptomatic COVID-19 elicits effective and long-lasting antibody responses in children and adolescents
- Can coronaviruses elicit long-lasting immunity?
- 60% may already have Immunity to COVID-19
- Pre-Existing T-Cells Stop COVID-19 Before it Starts
- Harvard: Immunity from mild COVID-19 infection much better than vaccination
- Natural Immunity Protected Tanzania and Zambia from COVID-19
- CD4+ Cross-Reactivity between Seasonal Coronavirus Colds and COVID-19
- Antibodies to COVID-19 can Exist in the Uninfected
References:
- Sheehan MM, Reddy AJ, Rothberg MB. Reinfection Rates Among Patients Who Previously Tested Positive for Coronavirus Disease 2019: A Retrospective Cohort Study. Clin Infect Dis. 2021 Nov 16;73(10):1882-1886. doi: 10.1093/cid/ciab234. PMID: 33718968; PMCID: PMC7989568.
- Spicer KB, Glick C, Cavanaugh AM, Thoroughman D. Protective Immunity after Natural Infection with Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) – Kentucky, USA, 2020 [published online ahead of print, 2021 Oct 12]. Int J Infect Dis. 2021;114:21-28. doi:10.1016/j.ijid.2021.10.010
- Kojima N, Klausner JD. Protective immunity after recovery from SARS-CoV-2 infection [published online ahead of print, 2021 Nov 8]. Lancet Infect Dis. 2021; S1473-3099(21)00676-9. doi:10.1016/S1473-3099(21)00676-9
- Kojima N, Shrestha NK, Klausner JD. A Systematic Review of the Protective Effect of Prior SARS-CoV-2 Infection on Repeat Infection. Eval Health Prof. 2021 Dec;44(4):327-332. doi: 10.1177/01632787211047932. Epub 2021 Sep 30. PMID: 34592838; PMCID: PMC8564250.
- Qureshi AI, Baskett WI, Huang W, Lobanova I, Naqvi SH, Shyu CR. Reinfection with SARS-CoV-2 in Patients Undergoing Serial Laboratory Testing. Clin Infect Dis. 2021 Apr 25:ciab345. doi: 10.1093/cid/ciab345. Epub ahead of print. PMID: 33895814; PMCID: PMC8135382.
- Leidi A, Koegler F, Dumont R, Dubos R, Zaballa ME, Piumatti G, Coen M, Berner A, Darbellay Farhoumand P, Vetter P, Vuilleumier N, Kaiser L, Courvoisier D, Azman AS, Guessous I, Stringhini S; SEROCoV-POP study group. Risk of reinfection after seroconversion to SARS-CoV-2: A population-based propensity-score matched cohort study. Clin Infect Dis. 2021 May 27:ciab495. doi: 10.1093/cid/ciab495. Epub ahead of print. PMID: 34043763; PMCID: PMC8241483.
- Vitale J, Mumoli N, Clerici P, et al. Assessment of SARS-CoV-2 Reinfection 1 Year After Primary Infection in a Population in Lombardy, Italy. JAMA Intern Med. 2021;181(10):1407-1408. doi:10.1001/jamainternmed.2021.2959
- Pilz S, Chakeri A, Ioannidis JP, Richter L, Theiler-Schwetz V, Trummer C, Krause R, Allerberger F. SARS-CoV-2 re-infection risk in Austria. Eur J Clin Invest. 2021 Apr;51(4):e13520. doi: 10.1111/eci.13520. Epub 2021 Feb 21. PMID: 33583018; PMCID: PMC7988582.
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