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How long after you’ve been infected with SARS-CoV-2 can you expect to possess immunity against the virus before you become vulnerable to reinfection?

new study done by the Yale School of Public Health has analyzed available data on natural immunity to estimate how often unvaccinated individuals can expect to become reinfected with COVID-19.

So, what is the average rate of Covid-19 reinfection?

The study found that, on average, unvaccinated people should expect to be reinfected with COVID-19 every 16 to 17 months.

The findings of the study contradict the notion that recovering from COVID-19 would guarantee a lifetime of protection from the virus.

This study looked at post-infection data from six coronaviruses that are close relatives to COVID-19, dating as far back as 1984. The time following infection ranged from around 128 days to 28 years under endemic conditions, meaning that the disease is constantly present in a population.

Using the data, the researchers were able to estimate the reinfection time for unvaccinated people — roughly 16 months on average. This is less than half the time it takes to get reinfected by other coronaviruses transmitted by humans, they found.

Already, people are increasingly reporting catching Sars-CoV-2 for a second or even third time in the present Covid-19 infections surges in England and Russia. 

The study suggested that the under-65s had about 80% protection for at least six months, while the over-65s had only 47% protection.

What is the average time of waning immunity against Covid-19 across multiple infected individuals?

recent study published on 6 October says that among 20,262 Britons who tested positive for Covid-19 in the period between July 2020 and September 2021, there were 296 reinfections, defined as a new positive test 120 days or more after an initial positive test – with an average time of 203 days between the positive tests.

However, the reinfection risk appeared to have been higher since May 2021 when Delta variant took over as the predominant variant.

Further data from the US, where various states have now started tracking and reporting on reinfection rates, supports the idea there is a substantially higher risk of re-infection with Delta.

In Oklahoma, which has a population of about 3.9 million, there were 5,229 reinfections reported during September (equivalent to a reinfection rate of 1,152 per 100,000) and reinfections have risen 350% since May.

How does the reinfection period compare for those who have natural immunity vs those who have been vaccinated?

The Yale study, led by Jeffrey Townsend, Yale professor of biostatistics, looked at post-infection data from six coronaviruses that are closely related to COVID-19, dating from 1984. The time following infection ranged from 128 days to 28 years under endemic conditions, meaning that the disease is constantly present in a population.

Using that data, researchers were able to estimate the reinfection time for unvaccinated people — roughly 16 months on average. This is less than half the time it takes to get reinfected by other coronaviruses transmitted by humans, they found.

“Reinfection can reasonably happen in three months or less,” Townsend explained in a university news release. “Therefore, those who have been naturally infected should get vaccinated. Previous infection alone can offer very little long-term protection against subsequent infections.”

How have the coronavirus variants affected the dwindling immunity over time?

New variants of SARS-CoV-2 such as the Delta variant, are more transmissible and resistant to vaccines. Available data shows that the longer it takes to stem the transmission of the virus, the more time these variants have to emerge and spread. This was seen in England when the reinfection risk appears to have been higher since May 2021 when Delta took over as the predominant variant.

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Sources:

https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(21)00219-6/fulltext

https://pubmed.ncbi.nlm.nih.gov/34627561/

https://covid.cdc.gov/covid-data-tracker/#county-view%7CConnecticut%7C9009%7CRisk%7Ccommunity_transmission_level

https://www.medrxiv.org/content/10.1101/2021.07.07.21260156v1.full


Jennifer Billings is the Medical Editor at Medicwell. She has 13 years of experience in internal medicine with a demonstrated history of working in the medical practice industry, both inpatient and outpatient urgent care. She has been published on Medicwell Blog, Medium.com, and is a regular contributor at MedCity News, Physician Family, and Psychology Today.