Japanese scientists have released a report saying people who were born before the 1918 flu pandemic seem to have immunity to the current swine flu, but not to the seasonal flu.

The research by a top University of Wisconsin flu researcher was released Monday and will be published in the journal Nature.

The 1918 influenza pandemic killed up to 100 million people worldwide. Those who survived the pandemic have antibodies against swine flu, or the A/H1N1 virus, the research said.

“I’m very concerned because clearly the (swine flu) virus is different from seasonal influenza,” said study lead Yoshishiro Kawaoka. “It’s a lot more severe.” But it is still not as severe as the 1918 influenza, he said.

A study from the Centers for Disease Control and Prevention (CDC) in May also found that one-third of senior citizens had some immunity to swine flu.

 The World Health Organization (WHO) in its updated A/H1N1 report on July 6 confirmed 94,512 officially registered cases and 429 deaths in 135 countries and territories worldwide.