Gail Jackson plunked down thousands of dollars for a family trip to a Mexican resort last year. Like many other travelers, she bought trip insurance in case someone had to cancel due to illness or for some other reason.

So, when her granddaughter learned that she was pregnant and her doctor advised her not to travel to Mexico because of an outbreak of the Zika virus, she stayed home and Jackson filed an insurance claim for her airfare.

It was denied.

While it would seem such a circumstance would be covered — her granddaughter had a note from her doctor, and birth defects associated with Zika infection are both well-documented and heartbreaking — the wording of the policy plainly seems to say otherwise.

Canceling because you are sick is covered. But the possibility that you might get sick at your destination — and seriously harm your unborn child — is not.

So, after spending days reading policies and talking to travel insurance professionals, a word of advice: Know what you’re buying.

There are two parts of your policy that are particularly important to read: the section that tells you what’s covered (“covered events’’) and what’s not covered (“general exclusions’’). In Jackson’s policy, these two sections are a mere 1,500 words.

In most policies, getting sick, injured, or dying (you or a family member) is covered, as is a traffic accident en route to your departure, an airline strike, job loss, order to appear in court, or theft of your passport. If your plans get torpedoed by a hurricane or other extreme weather, you are also covered. (However, there’s no coverage if you book after a storm becomes serious enough to acquire a name.) Explicitly not covered in most policies are suicide, mental breakdown, and intoxication, as well as “any issue or event that could be reasonably foreseen or expected.’’ Remember: Insurance is intended as a hedge against things that aren’t supposed to happen (like you dropping dead).

Trip cancellation insurance is one strand of travel insurance. You can also get coverage for losses if your trip is interrupted; you become sick and need medical attention far from home; you need emergency transportation home; or your baggage gets lost or damaged.

The cost of insurance is based on the cost and length of your trip, your age, and how long the insurance is to be in effect. The most common claim is for reimbursement of prepaid, nonrefundable airfare and other expenses after a trip is canceled due to something deemed unforeseeable.

The cost of insurance ranges from less than 5 percent of a trip’s cost to about 10 percent. On the Allianz Travel Insurance website, I punched in a one-week international trip during the Thanksgiving holiday for my wife and I. (Wishful thinking). We’re in our early 60s. On a $5,000 trip, top-shelf coverage costs $470 (9.4 percent); on a $10,000 trip, $970 (9.7 percent).

Some travelers buy trip insurance on their own online, which allows for shopping around in a competitive industry, but can be time-consuming and confusing. Many others buy through an airline, a travel company, or a travel agent.

Karen McCrink of Atlas Travel, one of New England’s largest travel companies, said most travel agents will walk you through what’s covered and what’s not. One thing she usually mentions is that travelers must be healthy when they buy their policy, or they might lose out. She recalled a man who booked a trip the day after hip surgery without telling her of his condition.

When he later had to postpone the trip because of a slow recovery, his claim was denied.

“Sometimes it pays to take a little extra time talking on the front end,’’ she said.

If you are spending $5,000 you really should think hard about buying it. If you are spending $10,000 you should think even harder. Still, it’s a personal choice. It depends on how risk-tolerant you are. The industry says about one-third of travelers purchase it.

It’s hardto not like Jackson and want to be on her side. At age 75, she’s got legions of friends, golfs in a summer league, and helps out with her children, grandchildren, and great-grandchildren. On a recent family vacation, she thrilled three generations by zip-lining into a lagoon.

A mental health counselor from Billerica, Jackson decided last year to do something special for her family. So she booked a vacation on the Yucatan Peninsula for more than 20 family members.

Several weeks later, one of Jackson’s granddaughters, married and the mother of two, found out she was pregnant. She would be in her seventh month by the time the Jackson clan departed.

If she decided to stay home, could Jackson get reimbursed for her airfare?

Turns out she couldn’t because pregnancy was listed as one of 20 “general exclusions’’ in her trip cancellation policy.

OK, but what about Zika? Isn’t that the kind of unforeseeable event that should be covered?

CSA Travel Protection, Jackson’s insurer, wrote: “Unfortunately, potential Zika exposure is not a covered event.’’

“She did the right thing by staying behind,’’ Jackson said of her granddaughter. “She felt bad but of course it wasn’t her fault. I just wish insurance covered it.’’

Bob Chambers, a CSA vice president, said most insurers give consumers 10 days after buying insurance to cancel without penalty.

“I recommend that they read it, but it’s a fact of life that very few people do,’’ he said.

.   .   .

I wrote last week about Denise Roney, who has gone without a car since June 9 because of MBTA bureaucratic lethargy. A T supervisor driving an agency SUV collided with Roney’s car while attempting to turn left against traffic in Lynn. That’s the kind of move that makes you presumptively at fault in a crash.

Roney tried for weeks, and then months, to get the MBTA to make good on her claim for repair of her car. But she couldn’t get a call back from the T, let alone a settlement check. After her plight was described in a front-page column on Aug. 25, the MBTA quickly found the T driver to be at fault and agreed to pay all damage.

The MBTA even apologized to Roney, but only indirectly.

“While claims are ordinarily processed expeditiously, that did not happen in this case,’’ the T wrote in an e-mail to me after the column appeared.

The MBTA “takes responsibility for the delay and apologizes to Ms. Roney,’’ it said, adding a promise to “make things right with [Roney] as quickly as possible.’’

When I mentioned the T’s apology to Roney, she was surprised. “They certainly haven’t reached out to me with an apology,’’ she said.

They should.

Sean P. Murphy can be reached at smurphy@globe. com. Follow him on Twitter @spmurphyboston.