Getting Your Second Dose of the COVID Vaccine? Here's What You Should Know

If you're awaiting your second shot of the coronavirus vaccine, chances are you've got some questions.

What are the side effects and when are you likely going to experience them? How long do you have to wait until you are fully vaccinated?

Here's a look at what you should know:

How long must you wait after receiving your second shot before you are considered "fully vaccinated?"

Complete vaccination is said to be two weeks after a person receives their second dose of the two-shot Pfizer and Moderna vaccines.

How effective is the vaccine after the second shot?

A new CDC study reported that a single dose of Pfizer's or Moderna's COVID vaccine was 80% effective in preventing infections. That number jumped to 90% two weeks after the second dose, the study on vaccinated health care workers showed.

When do you receive your second shot after getting your first one?

• The second Pfizer-BioNTech dose should be given 21 days after your first dose
• The second Moderna vaccine dose should be given 28 days later

According to the CDC, second shots should be administered as close to the recommended interval as possible, but can be given up to 42 days after the first dose, if necessary.

Though the CDC says second doses should not be administered earlier than the recommended interval, those given "within a grace period of 4 days earlier than the recommended date for the second dose are still considered valid."

Are you more likely to experience side effects after the second dose?

According to the CDC, side effects after your second shot "may be more intense than the ones you experienced after your first shot." 

"These side effects are normal signs that your body is building protection and should go away within a few days," the CDC states.

What are the side effects?

According to Pfizer, about 3.8% of their clinical trial participants experienced fatigue as a side effect and 2% got a headache. 

Moderna says 9.7% of their participants felt fatigued and 4.5% got a headache.

The CDC reports common side effects on the arm where the shot was administered include:

• Pain
• Redness
• Swelling

Common side effects in the body include:

• Tiredness
• Headache
• Muscle pain
• Chills
• Fever
• Nausea

"The Pfizer-BioNTech COVID-19 Vaccine and Moderna COVID-19 Vaccine both need 2 shots in order to get the most protection," the CDC states. "You should get the second shot even if you have side effects after the first shot, unless a vaccination provider or your doctor tells you not to get it."

“When people receive that second dose, they are receiving the second booster to try and reach the maximum efficacy," said Dr. Edward Cachay, infectious disease specialist at UCSD. 

Why do you experience side effects? Is it bad if you don't?

According to Dr. Mark Loafman, chair of family and community medicine for Cook County Health, the body's immune response creates the symptoms, but there's no real way to tell if you will experience side effects.

"That's simply a reflection of the immune response just the way we have when we get ill," he said. "From our immune response to a cold virus or a flu virus or the coronavirus, you know, it's our body's immune response that creates the illness. The virus itself is not the direct cause, it's directly causing the illness, and it's our inflammatory response making the immune system respond. And that's our body's way of destroying the virus is having inflammation and immunity to fight back. So that's the variation that's there and it's hard to know how you're gonna respond until you get it."

The good news is, if you do experience side effects, it's a sign your body is responding.

"The good news on our part is that a brisk response equals an effective response," Loafman said. "It tells us that the vaccine is working. Our body's forming a robust immune response and we feel that that's a positive thing. So we tend to see the vaccines that have a higher efficacy rate also have more of the so-called side effects or the symptoms because they work so well."

But if you don't, that's OK too.

"It's just that your body didn't react with as much of an inflammatory response," Loafman said. "You're still making antibodies. So it's not so much that sicker is better, but it just means that it's a vaccine that causes a reaction. Everybody - 95% of people who get it, almost 100% of people will get some reaction. Many of them that's an asymptomatic reaction, but others is more symptomatic."

According to Loafman, every person's response is unique.

"It's really just kind of a reflection of how unique each of our systems are, what other immunities we have," he said. "You know, a lot of the antibodies cross react and we have cross reactivity so it's really a mosaic. Each of our immune systems is a mosaic composite of all that we've been through and all that we have and all we've recently been dealing with. Our individual response varies. Everybody gets gets the appropriate immune response. The symptoms, you know, vary just like they do with with pretty much every infection you could think, from all the way from asymptomatic to potentially severe. That's all a sign of our individual immune systems responding to that to that exposure."

Are side effects an indication of whether or not you have already had COVID?

According to Loafman, there's some truth to the idea, but again, it depends.

"If you had COVID a while ago or you've already got some immunity, it's more like a booster," he said. "And boosters for some people are completely asymptomatic, boosters for other people trigger their immune response against it so they have some inflammation with it."

What can you do if you experience side effects?

The CDC recommends people talk to their doctors about taking over-the-counter medicines like ibuprofen, acetaminophen, aspirin, or antihistamines, for any pain and discomfort after getting vaccinated. 

"You can take these medications to relieve post-vaccination side effects if you have no other medical reasons that prevent you from taking these medications normally," the CDC states. "It is not recommended you take these medicines before vaccination for the purpose of trying to prevent side effects."

The CDC recommends you seek medical attention if you experience any of the following:

• If the redness or tenderness where you got the shot gets worse after 24 hours
• If your side effects are worrying you or do not seem to be going away after a few days
• If you get a COVID-19 vaccine and you think you might be having a severe allergic reaction after leaving the vaccination site, seek immediate medical care by calling 911.

If you get COVID between your first and second dose should you reschedule your second dose appointment?

According to Loafman, it is recommended that you reschedule.

"First of all, you know, you're already developing some natural immunity from the virus itself. So, the need for the vaccine is now delayed so there's no urgent need to do it because you already have immunity - natural immunity," he said. "And in addition, there is some concern that some patients will have worse side effects then, because they're still kind of recovering, they're still developing the initial immunity from the virus. So there's pain without the game, potentially."

According to Loafman, there's a window of time to reschedule.

"You have some time, a window, and it's thought to be a minimum two to three months of good, healthy immunity from the virus itself," he said. "So take that opportunity to convalesce and recover, and then get or finish the COVID vaccination when it will start to become helpful again."

But when will you know when you should reschedule?

Chicago's top doctor said the quarantine measures required for anyone who gets COVID still apply, regardless of vaccination.

"If you get COVID between your first and second vaccine dose, you need to isolate just like you would if you got COVID not related to your vaccine does," Chicago Department of Public Health Commissioner Dr. Allison Arwady said. "So if you get COVID you need to stay home for the full minimum of 10 days and until your symptoms have resolved, assuming that you had symptoms. Once your symptoms have resolved, once you're totally feeling better and you're no longer infectious, you can go ahead and get that second dose."

What can you do after you've received your second dose?

The Centers for Disease Control and Prevention recently updated their guidelines for vaccinated individuals.

The recommendations from federal health officials say fully-vaccinated Americans can gather with other vaccinated people indoors without wearing a mask or social distancing.

Here's a complete guide to what you can and cannot do once you are fully vaccinated.