New Delhi, Jan 3 : Existing vaccines are not as effective against Omicron as they were against the original virus, and thus boosters may help enhance immunity, health experts said here. The Omicron variant, being highly transmissible, has the potential to evade vaccine immunity. Data from various countries like South Africa and the UK has shown that it causes only mild illness. But as Omicron can surge infection cases, it can overwhelm an already burdened medical system. "Vaccines bypass natural immunity. The efficacy of existing vaccines is not as effective as it was against the virus that originated from Wuhan," Dr Sanjay Kumar Rai, Professor, Department of Community Medicine, AIIMS, New Delhi, said at a weekly health show by the New-Delhi-based HEAL Foundation on Sunday. "However, there might not be any severity if an Omicron infection happens," he said. The Indian Council of Medical Research also said recently that all Covid vaccines do not prevent infection and are primarily disease-modifying. "All Covid vaccines, whether they are from India, Israel, the US, Europe, the UK or China, are primarily disease-modifying. They do not prevent infection. The precautionary dose is primarily to mitigate the severity of infection, hospitalisation and death," said ICMR Director General Dr Balram Bhargava, at a recent press conference. At the same time, natural infection from Covid has can provide "long-term protection against the virus", Rai said. This has been consistent with several studies from across countries which showed that the durability of immunity post the Covid infection persists for about 9 months. Boosters may also help as they "enhance the quality of immunity," said Dr Nimesh Gupta, Chief, Vaccine Immunology Laboratory, National Institute of Immunology, under the Centre's Department of Biotechnology at the health show. "Persons vulnerable might fight Omicron with the current vaccines, but the elderly with compromised immunity won't be able to combat the infection," he added. With Omicron threatening vaccine efficacy, many countries pressed for booster doses. In India, Prime Minister Narendra Modi, last week, announced that healthcare/frontline workers, as well as elderly population (aged more than 60) with comorbidities, will get a precautionary dose from January 10 onwards next year. Meanwhile, with 175 new cases of the highly-transmissible Omicron Covid-19 variant detected in the last 24 hrs, India's tally on Monday rose to 1,700, with Maharashtra and Delhi continuing to be the worst-hit, according to the Union Health Ministry. On Monday, the country also logged 33,750 new Covid-19 cases in a span of 24 hours, with an additional 123 fatalities, taking the active caseload to 1,45,582. /IANS