Why You Can You Get COVID-19 Twice

Like most aspects of the COVID-19 pandemic, the question of reinfections, or subsequent infections with COVID-19, has been a moving target, especially as new variants have emerged.

The Rise of Reinfections

Early on in the pandemic, reinfections in individuals who had previously been infected with SARS-CoV-2 (the virus that causes COVID-19) were rare. But as the Omicron variant spread widely around the world, the number of people reinfected with the virus rose sharply.

In fact, in February of 2022, UK researchers found the risk of reinfection was 16 times higher when Omicron became the dominant variant compared to when Alpha or Delta were the main variants.

Waning Immunity

Why would reinfections rise with Omicron? The UK researchers point to two main reasons to explain the rise of reinfections as the pandemic waged. For one, our immunity from viruses tends to wear off with time. When we are infected with viruses, we are often protected from them for a while after infection, as our body has developed immunity through exposure to that virus. As time goes by, that protection may decrease, making us vulnerable to infection again. Some common cold coronaviruses have been shown to be able to infect the same person twice within 12 months.

The second reason has to do with the nature of variants. As SARS-CoV-2 evolves, scientists say 'immune escape' variants emerge. These variants are more effective at infecting people who had been infected with previous variants (or vaccinated). Omicron is an immune escape variant. It has numerous mutations that make it both more transmissible and better at escaping the immune system. Even so, vaccines are still effective at preventing reinfections. Though not yet peer-reviewed, a team of researchers at the Yale School of Public Health, found in January of 2022 that a third, booster shot still cuts the risk of Omicron infection by 50%.

Reinfection and Different Variants

This growing effectiveness of immune escape variants is precisely what scientists saw when they analyzed data on reinfections throughout the pandemic. Researchers in Qatar who shared their analysis of reinfection rates in NEJM in March of 2022, wrote that natural infection with the Alpha, Beta, and Delta variants of SARS-CoV-2 offers "strong protection against reinfection" (90.2% against the Alpha variant, 85.7% against the Beta variant, 92.0% against the Delta variant). However, the researchers saw only "considerable" protection against the Omicron variant (56.0%). Fortunately, among reinfected patients, none of the reinfections progressed to critical or fatal COVID-19.

A March 2022 UK study published in NEJM found that immunity acquired from infection with SARS-CoV-2 waned after one year in unvaccinated participants but remained higher than 90% in those who were subsequently vaccinated.

Scientists in Denmark also found that natural immunity offered higher levels of protection against reinfection, comparable with that provided by vaccines earlier in the pandemic. The results of their study (which was not yet peer-reviewed) showed that COVID-19-recovered individuals had a protection rate against reinfection of 83.5% during the Alpha period, 93% protection rate during Delta, but only 43% during the later Omicron period, suggesting that previous infections with other, earlier variants did not provide significant protection against Omicron infections.

Does this mean that if you were initially infected with Omicron, your chance of reinfection with Omicron yet again would be greater? Not necessarily. Though more research is needed to say for sure.

A preprint study posted in medRxiv in February 2022, meaning that it hasn't been peer-reviewed, found that while Omicron reinfections can occur shortly after the first infection, they are pretty rare. The large study looked at 1.8 million cases of infections that occurred during the Omicron wave. From a total of 187 reinfection cases, researchers identified just 47 instances of Omicron reinfections after an Omicron infection. These reinfections were mostly in young unvaccinated individuals with mild disease and did not result in hospitalization or death.

How to Stay Protected

Though COVID-19 reinfections are undoubtedly possible, there is a great deal of evidence that reinfections may be significantly less severe than initial infections. Of course, it's always important to remember that a person's age, immune health, vaccination status, exposure risk, and certain comorbidities may affect their reinfection rate.

The CDC states that COVID-19 vaccines protect people from getting seriously ill, being hospitalized, and even dying—especially people who have received a booster. Their guidelines recommend staying up to date with COVID-19 vaccinations.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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