As some Pennsylvanians skip second covid shot, experts caution one dose 'not enough'

Jun. 13—The increased availability of the covid-19 vaccine — and the myriad options for where one can receive it — has hampered efforts to track just how many people are skipping their second dose, which experts say is crucial to having the highest immunity possible against the virus.

Data from UPMC and Allegheny Health Network show about 5% to 10% of people aren't returning for second shots. Officials at Excela Health do not have data on the no-show rate for second-dose appointments, a spokesman said.

That number, however, can be deceiving, said Dr. Al L'Altrelli, administrative director of pharmacy at UPMC Presbyterian. He said health care workers at some organizations, such as UPMC, only can see which vaccinations took place within that health system.

"Where it looks like one person might not have gotten their second-dose vaccination, it could be very possible they got it somewhere else and we just don't have visibility into it," he said.

The 5% to 10% rate seen by UPMC is similar to what AHN has seen, spokeswoman Candace Herrington said. During one day this week, she noted, the second-dose no-show rate was about 10%, which has been the average.

AHN, too, assumes at least some of those people who missed their second dose have received the shot elsewhere. There also is the possibility that person is in the hospital or another skilled nursing facility or is traveling and has not yet rescheduled.

At the state level, no department is specifically tracking the number of skipped second doses, Department of Health spokeswoman Maggi Barton said.

"Anecdotally, we are hearing that some people have not shown up for second doses," she said. "But it is important to note that not every second dose is given exactly 21 days (Pfizer) or 28 days (Moderna) after the first dose, as people may need to change their second appointment for a variety of reasons."

She said the department continues to encourage anyone who received their first dose to return for their second.

Across the country, an estimated 5 million people missed their second doses of the Pfizer or Moderna vaccine, according to the New York Times and data from the Centers for Disease Control and Prevention.

The late April piece noted that 5 million represents about 8% of people who had received their first dose. That's about twice the number who missed second doses in the early days of the nationwide push for vaccination.

Some told the Times they feared the side effects of the second dose, which can mimic flulike symptoms in some. Others said they felt well protected with just one dose.

L'Altrelli said he's heard similar reasons.

"I think ... people get the first shot and they know that they have some protection. So there's an element of 'I have some protection' versus 'I've got that full maximum protection,'" he said. "It might just be a thought of, 'Well, I got something, that's better than nothing, and what's the benefit to a second one?'"

Some of that, he said, could come from a lack of education. He noted many of the vaccine-related education campaigns have been focused on the need to get the shot but failed to further explain why both shots are needed.

'Less protected'

The implications are wide, said Dr. Paul Offit, a University of Pennsylvania professor and member of the Food and Drug Administration's vaccine advisory panel.

"People who get just one dose are likely to be less protected and protected for a shorter amount of time than people who get the second dose," Offit said. "That's why it is so important to get a second dose."

What the second dose does, Offit explained, is induce a level of antibodies that's tenfold greater than the first dose.

The second dose also creates a particular type of cellular immunity. Dr. William Petri of the University of Virginia's Department of Medicine explained it like this in a January article on The Conversation: The first dose primes the immune system and shows it the virus, allowing the immune system to begin preparing a defense. The second dose lets the immune system ramp up both the quality and quantity of its antibodies and immune response.

"In the case of the Pfizer and Moderna covid-19 vaccines," he wrote, "the second dose increases the protection afforded by the vaccine from 60% to approximately 95%."

Offit said the overarching concern when vaccines rolled out was that health care professionals weren't going to be able to vaccinate people quickly enough, so they focused on getting one dose to as many people as possible.

"I think that sent the message, at least to some people, that one dose was enough," Offit said. "It's not enough."

Those without the second dose of the two-shot vaccines will be at risk down the line, as their protection will wane and "this virus isn't going to go away for a while."

Offit said the phenomenon of skipping the second of a two-dose vaccine isn't novel; only about 75% of people return for their second dose of the shingles vaccine. It's hard enough to get people to come in once for a vaccination, let alone twice, he said.

"I think people should be scared enough of this virus to know that if they're really going to be fully protected, they're going to need that second dose," he said.

Megan Guza is a Tribune-Review staff writer. You can contact Megan at 412-380-8519, mguza@triblive.com or via Twitter .