How is Our Own Immune System doing Against Covid-19 Reinfection?
A study was done in England, June 18, 2020, to January 11, 2021, using hospital workers to investigate whether our own antibodies developed against COVID-19 infection or COVID-19 exposure would protect a person from getting reinfected.
This knowledge of whether people who have recovered from Covid-19 are protected against reinfection and for how long, is essential to know in this fight against Covid-19 and determining herd immunity.
Final data was assimilated February 5, 2021, and published in The Lancet, April 9, 2021. Of note during this study is the UK variant B.1.1.7 emerged and spread and was accounted for in this study.
Study Enrollment Criteria
25, 661 participants were included in the study. Participants were divided into two groups as defined below upon enrollment:
1.Positive Cohort Group -8278 participants
a. Positive Antibodies
b. A past positive PCR
c. A past positive Antibody test
2.Negative Cohort group – 17,383 participants
a. Negative for PCR and Antibodies. All participants were required to have PCR and antibody testing every 2-4 weeks and completed questionnaires every 2 weeks on symptoms and exposures.
Criteria for Reinfection
A possible reinfection was defined as a participant with:
- Two positive PCR samples 90 or more days apart
- Or an antibody positive with a new positive PCR test at least 4 weeks after the first antibody-positive result.
Not a possible reinfection was defined as a participant with:
- Recurrent positive PCR results < 90 days apart who developed antibodies during this interval regardless of whether the latest positive PCR result was 4 weeks after the seroconversion.”
Outcomes
Positive Cohort Group 8278 participants. Those having had Covid.
- 155 reinfections
- 2,047,113 person days of follow up
- 7.6 reinfections per 100,000 person days
Negative Cohort Group 17, 383 participants
- 1704 became positive for Covid-19
- 2.971.436 person days of follow up
- 57.3 primary infections per 100,000 person days
The median interval between primary infections and reinfection was over 200 days or approximately 7 months which was the length of the study. Reinfection rates were not followed past the study dates, therefore, there is no data of immunity from prior Covid infections beyond 7 months.
Interpretation
- “Using a COVID-19 symptomatic case definition aligned with positive PCR results, previous infection reduced the incidence of infection by at least 90%
- Even when ‘all possible and probable reinfections were included, previous infection’ reduced the incidence of reinfection by at least 84%.
- We believe this is the minimum probable effect because the curve in the positive cohort was gradual throughout, indicating some of these potential reinfections were probably residual RNA detection at low population prevalence rather than true reinfections.
- Restricting infections to those who had COVID-19 symptoms, we estimated that participants in the positive cohort had a 93% lower incidence of new infection than did participants in the negative cohort.
- We have shown in this analysis that immunity from previous infection is protective against reinfection with the B.1.1.7 variant.
- Our findings of a 93% lower risk of COVID-19 symptomatic infection, after a longer period of follow-up than vaccines, show equal or higher protection from natural infection, both for symptomatic and asymptomatic infection.
After 7 months of follow-up, this large observational study showed previous SARS-CoV-2 infection protects most individuals against reinfection for an average of 7 months.“
Here is to Our Own Immunity!
Have an awesome day! Dr D
Happy Birthday Emily! This blog is dedicated to you and your persistent work in being the healthiest you can be!!