Scientists are reporting that the antibodies people make to fight the new coronavirus do not fade quickly.

The new study is the most extensive work yet on the immune system’s response to the virus and is good news for efforts to develop vaccines. The report published Tuesday in the New England Journal of Medicine. It was based on tests on more than 30,000 people in Iceland. It found antibodies lasted for at least four months after diagnosis.

The study also found that more severe cases of the coronavirus led to a stronger immune response to the virus.

"Among recovered persons, antibody levels are higher in older persons and in those more severely affected by SARS-CoV-2 infection," according to the research.

Independent experts say if a vaccine can spur production of long-lasting antibodies like that, it gives hope that immunity may not be fleeting. That's what some smaller studies previously suggested.

While the research was promising, it did also find that Icelanders are vulnerable to a second wave of the coronavirus even with the number of potentially immune citizens.