New York, Dec 1 : Although vaccine effectiveness for infection decreased sharply over time, especially during the Omicron period, the jab is crucial in preventing death among children and adolescents regardless of the predominant circulating variant, suggests a large study published by The BMJ. The researchers from Argentina said vaccinating children is an important public health measure that will continue to prevent deaths. It is already well known that mRNA and inactivated covid-19 vaccines are effective in preventing severe disease and infection in children and adolescents, but data on deaths are lacking. Waning protection against infection has also been described, especially for mRNA vaccines, but evidence for inactivated vaccines in children is limited. To fill this knowledge gap, researchers evaluated the effectiveness of two mRNA vaccines (Moderna and Pfizer-BioNTech) and the inactivated Sinopharm vaccine against Covid-19 related infection and death, and short term waning of immunity, in children and adolescents. Their findings are based on data for 844,460 children and adolescents (aged 3-17 years). The results show that estimated vaccine effectiveness against Covid infection was 61 per cent in children and 67 per cent in adolescents during the Delta period and 16 per cent and 26 per cent, respectively, during the Omicron period. Vaccine effectiveness declined over time, especially during the omicron period, from 38 per cent at 15-30 days after vaccination to 2 per cent after 60 days or more in children and from 56 per cent to 12 per cent in adolescents. Vaccine effectiveness against death related to Covid-19 infection during the Omicron period was 67 per cent in children and 98 per cent in adolescents. "In summary, vaccinating children is an important public health measure that will prevent mortality in this population, especially in periods of high viral circulation," the researchers said. /IANS