New Delhi, Dec 20 (IANS): A weaker immune system, old age and comorbidities can increase the risk of co-infection from Omicron and Delta variants of Covid-19 at the same time, said health experts on Monday.

Last week, scientists at the UK's Scientific Advisory Group for Emergencies (SAGE noted that some people have become infected by both the Delta and Omicron variants that are "operating separately as two epidemics" at the same time, making them seriously ill.

The possibility of a person being co-infected with both Delta and Omicron at the same time "is rare", Dr Dipu T.S, Clinical Associate Professor, Division of Infectious Diseases, Amrita Hospital, told IANS.

However, "it's not impossible to have confection of two strains, especially if the patient has an immuno-compromised status", he added.

Anecdotal reports have also suggested episodes of co-infection with two different strains of Covid-19 virus in the past.

"Even though Covid infections normally only involve one mutant strain, in extremely rare cases, it is also possible that two strains strike at the same time," Dr Namita Jaggi, Chairperson of Labs and Infection control at Artemis Hospital, Gurugram, told IANS.

But, co-infection can occur due to exposure to a large crowd with high chances of exposure to people infected with different Covid variants, she said adding "there is also a possibility that people who are recovering from Covid-19 may be at a higher risk of co-infection".

Further, some reports also have suggested that people living in areas with lower vaccination rates are at greater risk of getting co-infected. In addition, the risk of co-infection has been found more among the elderly, those with co-morbidities and a compromised immune system, Jaggi said.

The highly transmissible Omicron variant has to date spread to about 90 countries. The World Health Organisation (WHO) stated that it has "a growth advantage over Delta" and may soon overtake it. As per the SAGE, a successful new variant typically claims dominance by being much more infectious than previous strains, as has happened in the UK with Delta.

But can the combination of both variants lead to a super strain?

"It certainly can," Jaggi said.

"Viruses undergo a process known as recombination inside the body of the infected person. This occurs when viruses of two different parent strains infect the same host cell at the same time and exchange mutations during replication to produce a virus progeny that have some genes from both parents. The recombination might lead to the formation of a newer, more or less lethal variant," she said.

The risk of the combination events increases due to "huge, poorly controlled outbreaks because the number of infections is higher", Jaggi said.

However, according to Dipu, the chance of the strains "combining to form a super strain is bleak, considering the fact that the strains' co-existence is not of symbiotic nature but more of antagonistic in nature due to the varying type of immune activation which can be induced by different strains".

In its latest update, the WHO said there is still limited data on the clinical severity associated with Omicron.

So far it is known that people with Omicron can have the full spectrum of disease, everything from asymptomatic infection, mild infection, with people needing hospitalisation, but not oxygen support. Yet increase in cases means more hospitalisations, and overburdening of the healthcare system which can eventually raise further problems.

Dipu said that in a recent lab study it was found that the multiplication rate of the Omicron variant is high in the cells of nasal mucosa and less in the cells lining the lungs in comparison to the Delta variant.

"Hence though the virus multiplies at a higher pace, the chance of Covid pneumonia is less," he noted.

Further, data coming from regions like South Africa where there is rapid spread of Omicron have also favoured that the infection is milder compared to Delta. However, in the UK, Omicron cases have tripled and the country has also reported 12 deaths so far, in just a week. The first death due to Omicron was reported on December 13.

But the experts urged people to be vigilant and to get vaccinated. Besides, Covid appropriate behaviour at all times, wearing masks, must also be followed to keep Omicron at bay.

"It is critical that the vaccination programme for both doses be completed as soon as possible. The decision to give booster doses to frontline workers and paediatrics should be expedited by the government," said Dr. P.N Kakar, CEO, Park Group of Hospitals.

In addition, there is a need to increase surveillance and testing, as well as genetic sequencing, contact tracing, isolation, and quarantine, he said.