Los Angeles, Apr 29 (IANS): More than half of all Americans and about 75 per cent of children had been infected by Covid-19 by the end of February this year, according to a new study on antibodies by the US Centers for Disease Control and Prevention (CDC).

The CDC examined blood samples nationwide for a certain kind of antibodies, called anti-nucleocapsid antibodies, which are produced in response to Covid-19 infection but are not produced in response to Covid-19 vaccines, Xinhua news agency reported.

The researchers found that signs of past infection rose dramatically between December 2021 and February 2022, when the highly contagious Omicron variant surged across the country.

The most striking increase was in children. The percentage of those 17-years-old and under with antibodies rose from about 45 per cent in December to 75 per cent in February.

The reason leading to the greatest increase in this age group may be related to the lowest vaccination coverage, according to the CDC.

The older people were, the less likely they had evidence of past infections, the study found. That may be because older adults have higher vaccination rates and they may be more likely to take other Covid-19 precautions, such as wearing masks and avoiding crowds, according to the CDC.