Q: I am 72 years old and received my second COVID-19 vaccination two weeks ago. I am somewhat relieved to have this added protection, but others in my age group are reluctant to get vaccinated. I have heard the term “herd immunity” used in several updates on the news but am not sure what it means. Can you explain this term? Hopefully, it may help me convince my friends to get vaccinated.

A: A society reaches herd or community immunity when a sufficient percentage of the population has become resistant to an infection — either through vaccination or prior infection. Herd immunity can limit an outbreak of a specific disease because the risk of its spreading from person to person decreases.

While this term may not be familiar to many, it is not a new concept.

Herd immunity has been associated with many outbreaks over the years, such as the spread of polio in the 1940s and ‘50s, before a vaccine became available. Today, health officials report that polio is extremely rare, thanks to consistent immunization efforts.

To maintain herd immunity, we must continue to vaccinate. People who are immune protect themselves and the greater community.

For example, individuals with severe allergies or medical conditions who cannot get vaccinated are protected when the larger population achieves herd immunity.

Experts believe a society attains herd immunity when 80-95% of the population has been vaccinated, although this percentage varies by specific disease, according to health officials.

Your experience with some friends demonstrates the hesitancy regarding COVID-19 and other vaccines.

Everyone must make this personal decision. Encourage your friends to speak with their physician and to read as much information from trusted scientific sources as they can. And, above all, stay healthy!

Are you struggling to care for an older adult or having difficulty locating resources? Our staff is available to help. Visit us online at www.ESMV.org for more information. You can also call us at 1-800-892-0890ail ageinfo@esmv.org. Joan Hatem-Roy is the Chief Executive Officer of Elder Services of the Merrimack Valley and North Shore.