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00:00Vaccines protect individuals from severe illness, but they also help establish herd immunity,
00:10which safeguards the entire community.
00:12Here's how it works.
00:15Vaccines are not 100% effective, but they are a much safer way to become immune to a
00:19wide range of diseases than getting the disease itself.
00:25Take the seasonal flu.
00:27In a mostly unvaccinated community, an infected person passes the virus relatively slowly,
00:32a little more than one person at a time.
00:36COVID-19 is more virulent.
00:39Each person infected with the original variant spread it to two to three people at a time.
00:47Measles is one of the most contagious diseases.
00:50It spreads to 12 to 18 people at a time.
00:58Herd immunity occurs when a significant portion of a population becomes immune to a disease,
01:03reducing its spread and protecting those who are not immune, such as those who don't respond
01:09strongly to vaccines, those too young to get vaccinated, and those who are immunocompromised.
01:15More immunity means fewer infections and fewer spreading viruses.
01:20Spread immunity thresholds are calculated by the contagiousness of a virus.
01:26Twenty-three percent of the population needs to be immune to slow the spread of seasonal
01:30flu.
01:35Fifty to 67% need immunity to control the spread of COVID-19.
01:41And 92 to 95% need immunity to stop the spread of measles.
01:49Experts worry that mutations to viruses could make them even more transmissible and deadly.
01:54Without vaccine protection, communities can be quickly overrun.