Maybe on one level you can understand why a person would voluntarily get a first shot of a Pfizer or Moderna vaccine but then not go back for the second one.

I have heard some of the reasons, but they really don’t make sense to me.

The disturbing thing is that this is happening all over our area, too.

To add to this puzzling development, these are no isolated cases, but according to the Centers for Disease Control and Prevention, close to 5 million people have not returned for the second shot.

Locally, the Lehigh Valley Health Network reports that about 8% have skipped their scheduled second shot. This number shot up from March when LVHN reported that fewer than 3% were in this category.

I understand that some of these people figure that since the first shot is about 80% effective that this is good enough. This is especially true if a person has had any adverse reaction to the first shot.

What is not known, however, is how long the level of protection lasts when the second dose is delayed or missed altogether.

You must remember that the protocols are determined based on the studies these drug companies did, and in the case of Pfizer and Moderna, the studies involved two shots. That’s why public health officials strongly urge you get both shots, especially with new variants occurring here and abroad.

The incredible result of more than 90%-95% efficacy with both shots means that a person has a level of protection rarely seen with vaccines. Think of the flu vaccine, for example, which in some years has been less than 50% effective, but we still make it an annual ritual, because, even if we get the virus, it is generally less severe.

Some of those who failed to return for a second shot pointed to the fact that some vaccinated people contracted the coronavirus anyway. These cases are few and far between. No virus is going to be 100% effective, so with millions getting the vaccine there are some who will contract COVID-19 nonetheless, but, as with the flu, most of these cases are said to be less severe than they otherwise might have been.

Some point to the Johnson & Johnson single-shot vaccine, which was paused for a week or so in the United States, longer elsewhere, because of blood clots in some women between the ages of 18 and 48.

Here again, the odds are incredibly favorable that you are not going to be one of those affected. Medical professionals point out that women have a better chance of being struck by lightning than getting a blood clot with the J&J vaccine.

Most people are told when to report for their second appointment immediately after receiving the first shot. This is followed by reminders either through a text, email or phone call.

Health professionals are frustrated with the number of missed appointments for second shots. When contacted after they did not show up for their appointments, some said they had conflicts with other things they had to do. Some said they were ill or hospitalized, unrelated to COVID-19. Some will put off the second shot until they are no longer scheduled to travel or until after attending a special event, such as a wedding.

The problem with this approach, however, is that the efficacy of the Pfizer second shot is based on its being delivered two weeks later, while with Moderna it’s three weeks later.

The one good thing is that when there is a no-show, the health organization or sponsoring vaccine agency attempts to use the dosage on others so it doesn’t go to waste.

There are some who don’t like the side effects of the first shot and are concerned about the side effects of the second, said to be a bit more pronounced.

Some side effects such as chills, headache, pain, fatigue, redness and swelling are common. While the CDC acknowledges that side effects after the second shot may be more intense, it said that they are a normal sign that the body is building protection. In most cases, these symptoms disappear in a day or two.

Aside from the medical benefits of the full regimen of shots, think of the practical aspects. By missing the second shot, a person could create problems if workplaces, college campuses, airlines and cruise lines require proof of full vaccination at some point in the future.

By Bruce Frassinelli | tneditor@tnonline.com

The foregoing opinions do not necessarily reflect the views of the Editorial Board or Times News LLC.