Will people get a second COVID-19 vaccine?

A NEW POLL shows most Massachusetts residents are comfortable with eventually getting a COVID-19 vaccine. The results are good news, as health experts keep pointing out that even a vaccine with 95 percent effectiveness is only as good as its take-up rate by the population.

But it might be good to hold off on taking those COVID-now-vanquished victory laps.

That’s because while it may be heartening to learn that most in the state are willing to get a shot, it doesn’t answer an equally crucial follow-up question: Will they get a second one? 

As with many vaccines, the two COVID-19 immunizations nearing approval — from Pfizer and Moderna — both require two injections, several weeks apart. Based on experience with other vaccines, there are grounds for worrying about whether people will follow through and get the second shot. 

Vox reporter Dylan Scott says results are even worse for the HPV vaccine, recommended for adolescent girls to protect against cancers caused by the human papillomavirus. 

One added concern with COVID-19 vaccines is that, unlike hepatitis B vaccines, they can produce side effects, making some public health experts worried that unpleasant experience with an initial dose may keep people from rushing back for the second one. 

The best antidote for that behavior is probably just more public information telling people what they can expect from a vaccine — and urging them not to let any side effects dissuade them from getting the crucial second dose. 

A front-page Boston Globe story yesterday focused on a Boston ophthalmologist, Jorge Arroyo, who volunteered for the Moderna vaccine trial. He reported suffering aches and chills, lasting for about a day, after the second dose he received. (The trials were placed-controlled, so Arroyo doesn’t know whether he actually received the vaccine, but presumes he did.) 

Some people have mild symptoms following a flu shot, and the new vaccine against shingles, approved in 2017 and given in two doses, can cause an even stronger reaction. 

The side effects are, in a sense, not a bug but a feature of vaccines: They are a signal that the body is responding and beginning to produce antibodies. But that doesn’t eliminate the public health challenge.

Johnson & Johnson is working on a single-dose COVID vaccine. When it comes to the current two-dose drugs, it does appear that half a loaf is better than none: The Pfizer vaccine appears to be about 50 percent effective after the initial dose. (The full two-dose administration of both Pfizer and Moderna vaccines appears to be about 95 percent effective in preventing COVID.) 

The biggest reason for hope that COVID-19 vaccine take-up rates will be far higher than those seen with other immunizations is the fact that they are attacking a deadly global pandemic that has shaken life as we know in a way that no health crisis has in more than 100 years. 

Still, Ateev Mehrotra, an associate professor of health care policy at Harvard Medical School, told Scott there is plenty of reason for concern. 

Looking ahead, then, expect public health campaigns that don’t simply ask, “Did you get your vaccine,” but ask, “Did you get your two vaccines?”