In her thread, O'Donnell explained that her daughter could not get vaccinated herself because chemotherapy left her with a weakened immune system.
She also wrote that her daughter's exam room needed a "terminal cleaning", which interfered with other cancer outpatients' treatments.
O'Donnell also mentioned other potential risks of not vaccinating children, like other immuno-compromised children needing painful shots to bring up their white blood cell counts.
O'Donnell's thread illustrated what can happen when people skip out on vaccinations.
Dear parents of children who do not have cancer: a casual measles exposure in a grocery store caused the following things to happen when my child was in chemotherapy:— Nicole Stellon O'Donnell (@SteamLaundry) November 21, 2018
Vaccinating children with healthy immune systems prevents situations like the one O'Donnell's daughter went through, since these vaccines stop the spread of measles, polio, and other potentially deadly diseases, according to the Mayo Clinic.
These vaccines become especially important for children who cannot be vaccinated due to compromised immune systems or allergies to components of the vaccine, according to the Centres for Disease Control (CDC).
Vaccines contain dead or weakened strains of the respective disease each vaccine protects against, according to Nemours, a nonprofit children's health system.
When a person is vaccinated, the body creates antibodies that protect against the strain, so if a live version were to enter the body, a person would be better prepared to fight off the contracted disease.
Currently, the CDC recommends the measles vaccine for children 12 months and older.
Besides providing protection for yourself, vaccines can protect an entire community thanks to a concept known as "herd immunity," which means the more people who get vaccinated, the less likely a disease is to spread, according to the US Department of Health & Human Services (HHS).
When herd immunity is put into effect, even those who are unable to get vaccines will have a lower chance of getting a life-threatening illness.
O'Donnell did not immediately reply to INSIDER's request for comment.
This article was originally published by Business Insider.
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