DNA Explainer: Can Omicron reinfect patients who have recovered from COVID-19, what study suggests

The world, including India and European countries is witnessing a sudden surge in COVID-19 cases, mainly triggered by the new Omicron variant which was first detected in South Africa. Owing to a high number of mutations in Omicron, spread of the infection is faster. 

Preliminary results from lab studies showed that the Omicron variant is able to evade some of the protection against infection offered by COVID-19 vaccines. There are enough mutations in the right place in the Omicron variant to escape the maximal benefits of the vaccine, say study.

However, the good news is that the number of hospitalisations is less. Another important observation is that a large number of fully vaccinated individuals are getting infected by the variant. And this leads to a pertinent question that can the Omicron variant reinfect a person who earlier had been infected with the COVID-19 virus and subsequently recovered from it.

How well a previous infection will protect against Omicron?

One study suggests that people who recovered from a prior infection of COVID-19 have a significant risk of reinfection, much higher than with earlier variants.

A preprint study from South Africa found that risk of reinfection during the Omicron wave is substantially higher than the risk seen during the Beta and Delta surges.

Researchers used the country's extensive records of COVID-19 tests from March 2020 through late November 2021 to estimate the reinfection risk with Omicron.

They found that the risk of infection remained stable during the earlier surges caused by Beta and Delta, but increased dramatically since the arrival of Omicron.

The study observed that reinfection rates in people who had been infected during the previous waves was particularly high in case of previous infection with Delta.

However, reinfection rates like that of South Africa may not be the same elsewhere owing to different levels of vaccination, boosting and age distribution factors.

Other factors also can affect a person's risk of reinfection, including personal behaviours, public health measures like mask mandates and specific immune profiles.

Higher level of neutralising antibodies is better, but it is not clear yet what level is needed to provide a certain amount of protection or how it translates to the real world.

What WHO says

According to the World Health Organisation (WHO), Omicron can evade previous immunity in people and can still infect those who have had COVID-19 in the past.

It is definately an alarm for people who are unvaccinated and those who were vaccinated many months ago.

"Individuals who have recovered from Covid-19 are 3 to 5 times more likely to be reinfected with Omicron compared to Delta," the WHO said in the note released on its website last month.

The WHO said that the virus has been transmitted mostly among adults in their 20s and 30s, spreading initially in large cities and in clusters associated with social and workplace gatherings.

However, the good news is that there is no proof that Omicron causes more severe disease than the Delta variant, which led to a devastating second wave of infection last year.

The silver lining

A study confirmed that combination of widespread immunity and numerous mutations have resulted in the virus causing far less severe disease.

This report was based on the ongoing studies being conducted on Omicron, including in South Africa where the variant first emerged.

One of the crucial factors which makes Omicron less virulent is that it does not infect the lungs as easily as the previous variants like Delta.

One such study was published by a consortium of Japanese and American scientists, who experimented on mice and hamsters.

Another study in Belgium reported similar outcomes in hamsters, which experienced severe illness with previous mutations of the virus.