How long do vaccines last? The surprising answers may help protect people longer Science Mag
"In a 2018 review of 11 recent studies on the durability of influenza vaccines, researchers concluded that effectiveness can vanish as soon as 90 days after vaccination. The article, published in Clinical Infectious Diseases, further noted that 20% of Americans received their flu vaccines for a given season by the end of September—which means the vaccine may do nothing come peak flu spread in January and February... [example two] By the 2000s, the country had only a few hundred cases per year. But then in 2006, mumps surged on college campuses in the Midwest, with 6500 cases tallied before the year's end. Nearly 85% of the college-age people who became ill had received the recommended two doses of the mumps vaccine. Despite wide use of the vaccine, mumps outbreaks continue in the United States on college campuses and in tightly knit religious communities..." Implies the vaccine itself loses effectiveness, because a new mumps strain that has genetically "escaped" should strike other age groups just as often. In a dozen other studies of mumps outbreaks around the world, researchers have also found signs of waning protection."