Coronavirus: COVID-19 reinfection can occur sooner than you think; here's why immunity may wane faster

The Delta variant of SARs-CoV-2 virus wreaked havoc in many parts of the world, driving the surge in several countries, including India.

The Omicron variant of coronavirus on the other hand was much much milder, but it brought along high transmission rate and an increased rate of reinfection.

According to a December 2021 study conducted by scientists in South Africa, the risk of reinfection from Omicron is 3 times higher than it is for previous strains of the virus.

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Many researchers have looked into the phenomenon of reinfection and waning immunity. While many agree on COVID immunity lasting upto 90 days and beyond, there are those who have argued it could be shorter.

But before we jump into the details, let us first briefly discuss what COVID reinfection is and the role of immunity.

A repeated bout of infection is known as a reinfection.

When it comes to COVID-19, a new positive test result about 90 days after the last infection is said to be a COVID reinfection. It means a person was infected, recovered, and then later became infected again with the virus, says the Centers for Disease Control and Prevention (CDC).

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Following an infection, the body's immune system produces a robust immune response against the virus and retains the memory of it, which in turn protects against future infections.

According to the National Institutes of Health, "Immune cells and proteins that circulate in the body can recognize and kill the pathogen if it’s encountered again, protecting against disease and reducing illness severity.”

There are two types of immune responses triggered by the body. The first involves B cells that produce the antibodies, which is the first line of defense against an infection. Second is known as killer T cells, which are the second line of defense.

In contrast to the antibodies, T cells cannot see the virus, so it cannot stop it from entering the cells. However, they can identify the infected cells and can destroy it immediately before it replicates.

That said, these two aspects of immunity are what avoids severe COVID infections and minimizes the risk of reinfection.

According to a recent study published in the New England Journal of Medicine, immunity from a previous infection lasted for up to a year, whereas the protection offered by two doses of a Pfizer-BioNTech vaccine diminished at around six months.

The US CDC is also of the opinion that people who have had a confirmed COVID-19 infection in the past 90 days do not need to be isolated when they're exposed to someone with COVID-19.

But while evidence suggests natural immunity can last up to 90 days and beyond, a recent report by the CDC states COVID reinfection can occur sooner that you think. Let us find out how much sooner.

The small case series conducted by the U.S. Centers for Disease Control and Prevention (CDC) looked into 10 cases from four states namely Rhode Island, Vermont, Washington and Wisconsin. The patients had tested positive for the Omicron variant within 90 days of testing positive for the Delta variant.

Of the 10 people, 8 were younger than 18, one had received a two-dose mRNA COVID vaccine, six to 10 weeks before the primary infection. Two had got one COVID shot in the time between infections and the other seven patients were unvaccinated.

While the total length of time from initial infection to reinfection was found to be 23 to 87 days, with a median of 54.5 days. That said, the shortest time between infections was 23 days.

The US health agency says that the study findings might not be generalized to the U.S. population and that the data is restricted to the time period when Omicron became more dominant than the Delta.

"Nonetheless, this study highlights potential limits of infection-induced immunity against novel variants," the study states.

"Although the epidemiology of COVID-19 might change as new variants emerge, vaccination remains the safest strategy," it adds.

Both natural infection and vaccination can provide a certain amount of immunity against the SARs-CoV-2 virus.

However, experts believe new emerging variants and waning immunity has increased the risk of reinfection.

Since the Omicron variant was first detected, the number of coronavirus reinfection has been rising sharply, a trend not observed with previous variants. Experts believe the new variant probably has the ability to evade the body's immune defenses, which is why it is able to drive the surge.

Additionally, due to its heavy mutations, Omicron is also said to escape vaccine-induced immunity, causing increased chances of breakthrough infections too. Although one recent study from the UK Health Security Agency showed that protection against infection from two doses of vaccine may last for up to six months, the emergence of new variants and invariants is said to have impacted the efficacy of the vaccines.

Hence, experts have urged people to get their booster shots in time, since it is said to re-expose the immune system to the viral pathogen, triggering robust immune response.