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How To Make Sure People Come Back For Their Second COVID-19 Vaccine Dose

I cried at my desk this week. I could probably start every story I’ve written since February with that sentence but this was different. They were tears of joy and hope as I watched the first people in the world receive the newly approved COVID-19 vaccines.

[Related: How To Trust That A COVID-19 Vaccine Is Safe]

Now, those patients have an important task ahead of them: returning in a few weeks for a second dose. Two of the leading vaccine candidates — Pfizer’s and Moderna’s — require two doses to be effective, a daunting problem when you’re trying to vaccinate entire nations. How do you make sure everyone is coming back for their second shot? Our ability to stop the spread of COVID-19 depends on the answer. If people only get one dose, they will not be fully protected, but may behave as if they are. And even worse, there’s a fear that if enough people get only the first injection, the virus could develop resistance to the vaccine.

How COVID-19 vaccines work

But this isn’t our first time trying to get people to take multiple doses of a new vaccine: take the vaccine for human papillomavirus (HPV), for example. The way officials ensured most people made it to that all-important follow-up appointment for that vaccine may hold important lessons for our current efforts.

First approved for use in 2006, the vaccine to protect against HPV was slow to be adopted at first, with many parents concerned about the safety of a brand new vaccine. HPV can cause a sexually transmitted infection that can lead to genital warts or cervical cancer, and the vaccine against it requires two doses at least six months apart, or three doses for patients who get the first dose after age 15. (It’s typically recommended for preteens and teens.)

At first, many patients weren’t getting the full course of the vaccine. In 2008, 37.2 percent of adolescents1 had received the first dose of the HPV vaccine, while 17.9 percent had received all the recommended doses, according to an annual vaccine survey by the Centers for Disease Control and Prevention. By 2019, those rates had increased: 71.5 percent of teens had received at least one dose of the vaccine and 54.2 percent were up to date with the full course. While about one out of every four adolescents who started the vaccine series didn’t complete it, that’s better than a decade ago, when about half of those who got a first shot never finished the series.

That gap has been closing in part due to a number of strategies — most of them pretty simple.

“We did a study on why parents didn’t have their children complete the series and the most common reason was they weren’t reminded,”said Dr. Rebecca Perkins, an obstetrics and gynecology professor at Boston University. “They’d say, ‘Wait, I thought they were done.’ They just didn’t realize.”

Simple strategies like booking follow-up appointments at the time of the first dose, or sending reminders via text, phone or email, have been found to be effective in increasing the likelihood that patients complete the HPV vaccine course, and may be useful tools for making sure patients get both doses of the COVID-19 vaccine.

A review of this research in 2019 found that combining approaches (such as having doctors remind patients about the second dose when they visit, as well as providing text message reminders and setting up appointments) was most effective at increasing completion rates for the HPV vaccine. The CDC has required every state put together a COVID-19 vaccine distribution plan that includes strategies for ensuring patients come back for their second dose. Those strategies vary by state, but typically include some of the strategies that have proven effective for the HPV vaccine. States also already have vaccine database systems (with the exception of New Hampshire, though it’s building one now) that should make this easy to roll out, according to Dr. Marcus Plescia, the chief medical officer for the Association of State and Territorial Health Officials.

[What We Know About ‘Long COVID’]

“All states but one have vaccine registries and those have been scaled back up and expanded, which will allow states to know who has had the first dose, what they had, and where,” Plescia said. “But states can also use the registry proactively to send out reminders for people to come in for their second dose. They’re already used this way, often, for childhood vaccines.”

There are, of course, some important differences between HPV and COVID-19 vaccines. One is timing: The HPV doses are given months apart, while the COVID-19 doses are only spaced out by a few weeks. The population is different, too: The HPV vaccine is typically recommended for preteens and teens, while the coronavirus vaccine will be for everybody, but certain populations like medical workers, people with underlying conditions and the elderly will be prioritized. And perhaps the biggest difference of all: the urgency. The HPV vaccine is given to kids to protect them from a potential infection they might encounter at some point in the future. The COVID-19 vaccine is designed to stop an ongoing, deadly global pandemic. Those differences may make people more likely to come back for that second dose.

“We keep seeing the number of infections, the horrific death toll. It’s a constant reminder to people of the severity of this pandemic,” said Robert Bednarczyk, an epidemiologist at Emory University. “That helps people recognize the importance that, if they’re going to get vaccinated, they need to make sure they get fully vaccinated.”

So we hope. But there are reasons that patients might not come back for the second dose. Concerns about shortages may dissuade people, according to Bednarczyk, so health networks should offer patients backup locations at which to get their second shot in case the first location is running low. There’s also the risk of side effects. Both the Moderna and Pfizer vaccines can cause fever or aches, which might make people less keen on coming back for another jab.

The pandemic’s urgency is such that experts say we should be making every effort to ensure complete coverage of those who decide to get vaccinated. The stakes are incredibly high, so why not pull out all the stops?

[Related: What A Summer Of COVID-19 Taught Scientists About Indoor vs. Outdoor Transmission]

There are also other ideas being floated, too, including incentivizing patients with cash. The idea is that if we give people a financial incentive only for the second dose of the vaccine, we’ll increase the likelihood of completion. Ex-congressman and former presidential candidate John Delaney suggested the government offer a substantial cash reward of $1,500 for completing the vaccine series, as a stimulus check and vaccine incentive in one. Dr. A. Mark Fendrick, the director of the University of Michigan Center for Value-Based Insurance Design, says a much lower investment could do the trick.

“I’m a little more fiscally modest and think somewhere between $25 and $50 would effectively move the needle,” Fendrick said, adding research shows this can be effective. “As my mother would say, ‘I can’t believe you have to do research to show if you pay people to do something they’ll do it more often than if you don’t pay them.’”

Given these are new vaccines, and the country is facing one of the biggest widespread public immunization efforts in half a century, there are a lot of unknowns. This will be a massive undertaking, but the stakes couldn’t be higher.

COVID vaccine delivery day


  1. Ages 13 to 17.

Kaleigh Rogers is FiveThirtyEight’s technology and politics reporter.