If you can’t get a second vaccine appointment within 28 days of your first, don’t panic

Monitor staff
Published: 2/6/2021 1:01:35 PM

When Peter Minkow logged in to schedule an appointment for his second dose of the COVID-19 vaccine, he immediately became flummoxed.

The 76-year-old from Laconia received his first Moderna shot on Jan. 26, which meant his second dose, according to federal guidance, should be administered within 28 days, sometime in late February. The earliest appointment available was March 17.

He decided to make a gamble – he canceled his March 17 appointment in the hopes that an earlier one within the 28-day time frame would open up. Every time he refreshed the page, though, the available appointments were later and later at locations farther and farther away from his Laconia home.

He gave up and selected an appointment in April, nearly three weeks later and 40 miles away from his initial appointment.

“It’s just maddening,” he said. “I took the gamble and lost.”

Many Granite Staters who, like Minkow, found themselves with appointments outside of the recommended 28 days slid into a panic. They wondered, will my vaccine be less effective? Will I have to start the vaccination process all over again?

The short window between the first and second dose of the COVID-19 vaccine has been the subject of so much anxiety and logistical reworking, it begs the question: on a scientific level, how much does strictly abiding by the recommended timeframe – 21 days for Pfizer and 28 days for Moderna – really matter?

To answer this question, it’s useful to understand how the vaccines work.

The Pfizer and Moderna vaccines capitalize on proteins that sit on the surface of the coronavirus, called spike proteins, which allow the virus to attach to and infect human cells. When you’re injected with the first dose of the vaccine, tiny pieces of genetic material that code for these spike proteins make their way into your cells.

Millions of these harmless proteins are produced, prompting a response from the immune system. The body deploys antibodies which clumsily attempt to bind and kill the proteins. But, having never encountered this particular molecule before, the immune response is rather crude.

After the first dose, both Pfizer and Moderna are between 65% and 75% effective.

That’s where the weeks between the first and second dose play an important role.

During the next month or so, the cells that create antibodies undergo a period of rapid mutation. Over several iterations of these cells, antibodies become more and more specialized to attach to coronavirus spike proteins.

When the second dose is injected, the mutation process starts all over again, ultimately leading to a response so tailored to COVID-19, that the effectiveness jumps to 95% within a couple of days of the shot.

David Topham, a professor of immunology at the University of Rochester Medical Center in New York, has studied for decades the period of time between initial and follow up booster shots.

While it’s critical that second doses aren’t administered too soon after the first dose, Topham said there’s no real danger to waiting longer than the recommended 21 or 28 days.

In fact, many studies, particularly with influenza, have found that if you wait longer between the first and second dose, the vaccine becomes more effective, he said. For avian influenza, a comparable virus because of its novelty to the body, the research seems to suggest the optimal time between doses is three to six months.

Of course, there are other reasons you might want to get your second dose sooner rather than later. The longer you walk around with 52% protection, rather than 95% protection, the more likely you are to fall ill with COVID-19.

That’s partly why Topham thinks federal agencies have advised about a month in between doses – during a global pandemic, the main goal is to get as many people as much protection as quickly as possible.

“There’s no real science behind why we do it in three weeks or four weeks,” he said. “I know this sounds crazy, but it’s arbitrary. If you look for literature that documents why that’s the best time point, there isn’t any.”

In late January, the Centers for Disease Control and Prevention altered their vaccine recommendations to allow doses to be spaced six weeks if administering the shot in the four week window “is not feasible.” For many states, including New Hampshire, limited vaccines from the federal government has made it difficult to get everyone an appointment within their three to four week window.

The Granite State has been receiving about 17,000 doses of the vaccine per week – a number dwarfed by the 300,000 residents currently eligible for the shots. As of Jan. 29, the state had only 6% of the doses they need to vaccinate everyone in Phase 1B.

Namone Pike, the system director of clinical pharmacy at Dartmouth-Hitchcock Medical Center, said it’s still important to stick to these time windows as closely as possible because the effectiveness of these time frames are supported by rigorous clinical studies.

“We don’t have much data but there is no maximum interval,” she said.

After a couple of days of checking the online registration website, Minkow was able to reschedule his appointment within the recommended timeframe.

For those who aren’t as lucky, Topham said to remain calm.

“When people say they’re worried about getting their second dose on time, I say they shouldn’t worry, as long as they get the second dose eventually,” he said. “It’s not going to be a detriment to their ultimate immune response. If anything, it might actually be better.”




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