You may feel lousy after getting the COVID vaccine. Experts say that's OK

The first shots in arms of the COVID-19 vaccine mark a major step towards post-pandemic normalcy. But their advent in turn prompts further scrutiny and concern over possible side effects.

Public health officials warn you may feel COVID-like symptoms after your injection -- and that’s normal.

“I think the first thing we need to tell people is that this is not COVID. Don't worry about that. You can't get COVID from the vaccine,” Dr. William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center, told ABC News. “These side effects are really a manifestation of your immune system starting to come to grips. It shows - 'Whoa, my system is working -- not bad.'”

Long-term side effects from vaccines are extremely rare. Bad reactions typically happen within a few weeks of receiving a shot, and side effects will likely be worst within the first 24 to 48 hours following injection, experts say. Those may range from fatigue, head and body aches, fever, chills or nausea, enough to put someone out of commission for a day or two, but experts say those symptoms are normal.

“Immunization is an attempt to sort of trick your body into thinking that you’ve had an actual infection,” Dr. John Brownstein, chief innovation officer at Boston Children’s Hospital, Harvard epidemiology professor and ABC News Contributor, said. “So it’ll give you a feeling like you're sick, but in fact, you're not.”

“It's rare they’re severe, but it may be some people feel sufficiently puny that they need either a light schedule the following day, or they may even need to stay home from work,” Schaffner said.

But taking that sick day to recoup is easier said than done for many Americans who are barely making ends meet during the health crisis’ economic fallout.

Health experts are concerned that the prospect of unpleasant side effects could deter too many from coming back for their second dose -- or taking the vaccine altogether. Calls for an “open, even-handed discussion” and transparency about potential side effects has flecked discussion of the vaccines’ authorization, and the need to demystify any adverse reactions ahead of time.

"I wish the immune system had a better public relations team working because, I mean, it's just a natural consequence of having an activated immune system," Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, said at a recent Journal of the American Medical Association Network discussion. "But I think it does matter because you're not going to vaccinate your whole emergency department, and have them potentially be out the next day."

The “risk-benefit” profile for both leading vaccine candidates has proven promising with early findings. The U.S. Food and Drug Administration said Tuesday there was strong evidence the Moderna vaccine was both safe and effective; coming days after the vaccine from Pfizer and BioNTech received FDA emergency use authorization.

In prepping to administer their first doses, hospitals have strategized their 1A frontline groups, gaming out the doses so they don’t take an entire ward out of commission. Northwell Health, New York’s largest hospital system, told ABC News it's developed an algorithm to equally distribute who gets the first wave of shots, which will be cross-referenced by job description, the facility they work at and their age.

“This will be a major effort, and we can’t remove staff from taking care of patients,” Dr. Mark Jarrett, Chief Quality Officer at Northwell Health, told ABC News. “And it’s occurring at a time when the virus is surging back, perhaps with a vengeance -- so we have to be prepared to take care of both.”

And for some on the frontlines battling a virus that has now claimed over 300,000 American lives, potential side effects attending a vaccine’s protection far outweigh the still-unknown long-term ravages COVID-19 may have on the body.

Dr. Victoria Smith, family physician on the Ochsner Health Board of Directors, based in New Orleans, volunteered for phase 2/3 of the Pfizer trial. For her, getting the vaccine was “less scary” than the battle against coronavirus.

“It's not just -- I could die from COVID --, but also, I could be infected with COVID and then end up with long-term effects that nobody really knows how to treat,” Smith told ABC News for the 20/20 special, “THE SHOT: Race for the Vaccine." “So weighing, being a COVID long hauler, death, I'll choose the risk of a vaccine.”

“Now, tighten your seatbelt. There could be bumps in the road, and we need to keep a critical eye to make sure that the vaccination program continues to be safe,” Schaffner said. “But -- you have to see it in comparison to what a day of fatigue is -- a whole lot easier than having to wear a ventilator in an intensive care unit.”

This report was featured in the Wednesday, Dec.16, 2020, episode of “Start Here,” ABC News’ daily news podcast.

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