The side effects from the second dose of the COVID-19 vaccine might pack more of a punch than the first one, local health leaders confirmed Friday.

It only happens for about 20% of patients, they said, and it’s not a reason to avoid getting vaccinated, but it’s important to know what to expect when you get the shot.

“We’ve got to be honest and straightforward,” said Dr. O’Dell Owens, a longtime physician who now runs the Cincinnati health advocacy group Interact for Health. “The second shot’s a little harder on you than the first for some people.”

Reported side effects of both the Moderna and Pfizer vaccines, both of which are delivering in two doses spaced weeks apart, include aches, chills, fever and fatigue. A patient might experience any of these side effects from their first shot, but they appear to be stronger after the second.

Why? Here’s the short version.

The COVID-19 vaccine is an mRNA vaccine that teaches the recipient’s cells to make a harmless piece of the “spike protein” found on the surface of the virus that causes COVID-19. The vaccine cannot cause a recipient to develop COVID-19, but the presence of the foreign protein still triggers an immune system response.

The body produces antibodies that can fight the virus, and the patient is protected from illness without ever having to catch the novel coronavirus.

The demanding internal process of shoring up the immune system and making those antibodies is what causes most vaccine side effects, not the virus.

What's mRNA?
Good question — it's been a few years since we were in high school biology, too. mRNA is "messenger RNA," a type of molecule that contains genetic instructions for building a particular type of protein. These instructions are "read" by other cells, which create the protein in question. The RNA part stands for "ribonucleic acid," a basic building block of life. All living things need mRNA to survive.

READ MORE about mRNA vaccines via the Centers for Disease Control and Prevention

Dr. Carl Fichtenbaum of UC Health compared the immune system to a boxer. Good fighters protect themselves more ferociously after taking a punch — so do bodies that receive more than one dose of a vaccine, even when a two-dose system is necessary.

“The response is often a little bit more powerful, more vigorous and more quick,” he said. “That's why, when people get the second vaccine, many times they feel a little bit worse than when they got the first vaccine."

Dr. Phillip Hartman, a St. Elizabeth physician who received his second dose Wednesday, said he had not experienced any notable side effects.

The rate of patients who do is around 20%, and in some cases they might not feel well enough to work for a day or two. Hartman said that’s expected.

“It’s really a minimal inconvenience to where you’re going, especially when you consider I treat patients that had COVID six months ago and still aren’t breathing right,” he said.

Owens said he hopes telling people what to expect will keep them calm and knowledgeable about the process, making them less vulnerable to scare tactics or conspiracy theories.

“I’m so afraid that some people are going to say, ‘Oh, look what happened to me,’ and you won't have these people coming back on time for their second shot, and that's important,” he said.

Between the COVID-19 vaccines' two required doses, the clock is ticking.

Food and Drug Administration guidance indicates the vaccine's second dose should be administered three to four weeks after the initial dose, but Tri-State health officials and experts said there is no guarantee there will be enough supply to meet that timetable for the thousands who have already received their first dose.

"You're going to have a little competition for that seat," said Dr. O'Dell Owens, CEO of Interact for Health.

According to the FDA, an individual is 95% protected from contracting the disease if the Pfizer vaccine's second dose comes 21 days after the first; for the Moderna vaccine, that time period is 28 days. But with demand outpacing supply, clinics aren't giving vaccine recipients guarantees about when they can get the second dose.

Hamilton County Health Commissioner Greg Kesterman said there is some wiggle room.

"If you can't get your dose for a week later or even a couple weeks later, it is acceptable still to get your second dose," he told WCPO.

But he also added there is still uncertainty swirling around the vaccine.

"Unfortunately, all of the vaccine that's currently available has not been studied long enough to know all of the ins and outs of how the vaccine works," he said.

For people like Dorothy Darden, who feel hesitant about getting the vaccine, Kesterman said they have options.

"I really want to discuss it with my doctor more before I would even determine that I would to get it," Darden said.

Kesterman said, for now, the county is capable of administering second doses to county taxpayers who might have received their first dose elsewhere, but they have to register to do so.

Researchers expect vaccine supply to spike as soon as next month when a third vaccine, under development by Johnson & Johnson gets approval and begins distribution.

Ohio isn’t tracking the number of fully vaccinated people who have contracted COVID-19. Instead, the state collects data about how many people with these “breakthrough” infections have been hospitalized or died.

At first glance, it may seem like something here is missing, but Ohio’s chief medical officer says less is actually more. He also said the CDC takes the same approach.

“When you think about this from an information- or data-gathering point of view, it is much more reliable to look at those endpoints of hospitalizations and deaths,” Dr. Bruce Vanderhoff said. “Endpoints which really and truly tell us if the vaccination is doing what it was designed to do or not.”

Indiana is taking a different approach. The state tracks the number of breakthroughs to compile a total number of cases, but the method is somewhat non-traditional.

The data is pieced together in a painstaking way by comparing two separate databases. Staff members look at a registry of every vaccinated Hoosier and a spreadsheet of daily positive COVID test results. Then they crunch the numbers and post weekly totals for the public online.

Dr. Thom Huth, who works for Reid Health in Wayne County, Indiana, said he can see how having separate ways to track these cases can be confusing.

"It unfortunately may create the impression that authorities don't know what they're doing,” Huth said. “But that's not the case. It's just that the needs are changing so quickly. It's hard for anybody to keep up.”

He also said tracking individual breakthrough cases is tricky and can be unreliable.

"One recent day, 10% to 15% of the patients in the hospital had been previously vaccinated,” Huth said. "But that number goes up and down."

Ohio Governor Mike DeWine said he supports the way Ohio gathers its data on these breakthrough cases and fear of discouraging vaccination plays no part in how the state collects numbers. DeWine said top health advisors, including those at the CDC, think it’s more important to track hospitalizations and deaths of fully vaccinated people.

Dewine said the focus should remain on boosting vaccination numbers, a sentiment former Cincinnati health commissioner Dr. O’dell Owens agrees with.

"The key part is to keep people out of the hospital,” Owens said. “We’ve got to stay focused on one thing. If everybody's vaccinated, there are no breakthrough cases.”