It’s not a bad sign if you feel fine after your COVID-19 shot. Luis Alvarez/DigitalVision via Getty Images
Robert Finberg, University of Massachusetts Medical School
If someone gets a headache or feels a bit under the weather after receiving a COVID-19 vaccine, it’s become common to hear them say something like “Oh, it just means my immune system is really working hard.” On the flip side, when people don’t notice any side effects, they sometimes worry the shot isn’t doing its job or their immune system isn’t reacting at all.
Is there any link between what you can notice after a vaccine and what’s happening on the cellular level inside your body? Robert Finberg is a physician who specializes in infectious diseases and immunology at the Medical School at the University of Massachusetts. He explains how this perception doesn’t match the reality of how vaccines work.
Your immune system responds to the foreign molecules that make up any vaccine via two different systems.
The initial response is due to what’s called the innate immune response. This system is activated as soon as your cells notice you’ve been exposed to any foreign material, from a splinter to a virus. Its goal is to eliminate the invader. White blood cells called neutrophils and macrophages travel to the intruder and work to destroy it.
This first line of defense is relatively short-lived, lasting hours or days.
The second line of defense takes days to weeks to get up and running. This is the long-lasting adaptive immune response. It relies on your immune system’s T and B cells that learn to recognize particular invaders, such as a protein from the coronavirus. If the invader is encountered again, months or even years in the future, it’s these immune cells that will recognize the old enemy and start generating the antibodies that will take it down.
In the case of the SARS-CoV-2 vaccines, it takes approximately two weeks to develop the adaptive response that brings long-lasting protection against the virus.
When you get the vaccine shot, what you’re noticing in the first day or two is part of the innate immune response: your body’s inflammatory reaction, aimed at quickly clearing the foreign molecules that breached your body’s perimeter.
It varies from person to person, but how dramatic the initial response is does not necessarily relate to the long-term response. In the case of the two mRNA COVID-19 vaccines, well over 90% of people immunized developed the protective adaptive immune response while fewer than 50% developed any side effects, and most were mild.
You may never know how strongly your body’s adaptive immune response is gearing up.
The bottom line is you can’t gauge how well the vaccine is working within your body based on what you can detect from the outside. Different people do mount stronger or weaker immune responses to a vaccine, but post-shot side effects won’t tell you which you are. It’s the second, adaptive immune response that helps your body gain vaccine immunity, not the inflammatory response that triggers those early aches and pains.
Side effects are normal responses to the injection of a foreign substance. They include things like fever, muscle pain and discomfort at the injection site, and are mediated by the innate immune response.
Neutrophils or macrophages in your body notice the vaccine molecules and produce cytokines – molecular signals that cause fever, chills, fatigue and muscle pain. Doctors expect this cytokine reaction to happen any time a foreign substance is injected into the body.
You might not notice any symptoms at all after your COVID-19 vaccine. SOPA Images/LightRocket via Getty Images
In studies where neither recipients nor researchers knew which individuals were getting the mRNA vaccine or a placebo, approximately half of people aged 16 to 55 who received a SARS-CoV-2 vaccine developed a headache after the second dose. This reaction may relate to the vaccine – but a quarter of people who received just a placebo also developed a headache. So in the case of very common symptoms, it can be quite difficult to attribute them to the vaccine with any certainty.
Researchers anticipate some reports of side effects. Adverse events, on the other hand, are things that physicians do not expect to happen as a result of the vaccine. They would include organ failure or serious damage to any part of the body.
The blood clots that triggered the U.S. to pause distribution of the Johnson & Johnson vaccine are a very rare event, apparently happening with one-in-a-million frequency. Whether they are definitely caused by the vaccine is still under investigation – but if scientists conclude they are, blood clots would be an extremely rare side effect.
The only “active ingredient” in the Pfizer and Moderna vaccines is the mRNA instructions that tell the recipient’s cells to build a viral protein. But the shots have other components that help the mRNA travel inside your body.
To get the vaccine’s mRNA into the vaccinated person’s cells where it can do its job, it must evade enzymes in the body that would naturally destroy it. Researchers protected the mRNA in the vaccine by wrapping it in a bubble of lipids that help it avoid destruction. Other ingredients in the shots – like polyethylene glycol, which is part of this lipid envelope – could cause allergic responses.
Scientists haven’t identified any relationship between the initial inflammatory reaction and the long-term response that leads to protection. There’s no scientific proof that someone with more obvious side effects from the vaccine is then better protected from COVID-19. And there’s no reason that having an exaggerated innate response would make your adaptive response any better.
Both the authorized mRNA vaccines provided protective immunity to over 90% of recipients, but fewer than 50% reported any reaction to the vaccine and far fewer had severe reactions.
[Insight, in your inbox each day. You can get it with The Conversation’s email newsletter.]
Robert Finberg, Professor of Medicine, University of Massachusetts Medical School
This article is republished from The Conversation under a Creative Commons license. Read the original article.
In The News
>WEATHER: Mark Rosenthal's 7-day forecast (:30). High of 90, afternoon storms today in Worcester
-Worcester opens cooling centers Tuesday amid high heat
>TOP OF THE NEWS
+5:00: Mistrial declared in Worcester Tech grad's "Cop City" racketeering case
+5:00: After delay, Crompton Park Pool in Worcester expected to open Friday
+5:00: Worcester County Wonders: Worcester's only working farm remains
+5:00: Radio Worcester Roundtable (44:06): Rent incentives, pool closures and Worcester’s political future
+Noon: This year's Shawna Shea Film Festival in Worcester could be best ever
+Noon: Worcesteria: Bright lights, big city U.F.O. reports
+Noon: Janice Harvey: Talking about politics at the cookout, and other bits of summer advice
-Police: Man carjacks woman at Dairy Queen drive-thru (1:30). Article
-Related: Surveillance video shows Dairy Queen carjacking suspect moments before attack (1:33)
-Related: Suspect in Dairy Queen carjacking was on bail for attempted murder charge
-Man killed in Worcester shooting remembered for being "the best dad to his boys"
-Boys 14 and 16 pull gun on Worcester cabbie, police say
-Loaded stolen gun found after Worcester car meet-up
-Former barbecue restaurant in Worcester to become sister restaurant of popular healthy eatery
-Monday's Child: Laren, 10, is a friendly, fun-loving and energetic young girl who brings joy
-Meghan Montaner is appointed new executive director of Mechanics Hall
-Radio Worcester's The Rundown (24:19): WPI keeps hotel, library safety, and state sues over mental health funds
>DINING OUT (brought to you by Patsie Dugan's): TODAY! Worcester restaurant reopens after renovation
-ICYMI: Worcester restaurateur defends staff after brutal review
-Elm Park playground rehab finished ahead of schedule
-Developer planning 185-apartment Canal District complex buys parcel for $5.3 million
-5 homes sold for over $1 million in Shrewsbury over last 2 weeks
-See the rest of the day's Worcester news
>HOLDEN (brought to you by Lamoureux Ford): TODAY! American Legion Post 42 meeting at 2:30
-Teen driving BMW without front plate stopped in Holden, cited for license suspension and plate violation
-Lamoureux Ford offers huge discounts! (2:53)
-This week's road closures and traffic delays
>THE BURBS (brought to you by North End Motor Sales): Rutland man charged after police say he kicked cars, confronted officer
-300-unit 40B development at Shrewsbury’s 104 Main Street reaches Zoning Board
-Tractor-trailer crashes off Mass. Pike into tree line in Charlton (:16)
-Brimfield Antique Flea Market's July show is this week
-5 residential Northbridge properties bought for $3 million
-Paxton override election set for September
-Woman crochets as tribute to her mother
-Clinton Middle School announces honor roll
>BARS & BANDS: The Mayor's Live Music List for Tuesday
-Happy hour, long banned in Mass., gets public hearing (2:18)
>SHOWTIME: Blue Man Group wraps up 30 years in Boston
-Sterling’s Jonathan Godbout talks Ninja Warrior journey, grit and TV appearance (18:44)
-Broadway in Worcester announces star-studded season featuring Tony winners (8:43)
>OPINION: Luis G. Pedraja: Democracy, education go hand in hand
-Jennifer Julien Gaskin: The Divine Seven — Walking with my protector still
-WCCA-TV's Perspectives No. 100 (27:28): Footage from Gaza
>OBITUARIES: Tribute to woman who worked at Colony Retirement Homes for more than 40 years
>SPORTS: Jayson Tatum’s Achilles injury rehab continues with pool workout
-Bill Belichick nearly made Stephon Gilmore cry in front of Patriots
-Red Sox beat Rockies, 9-3
-After 2 years away from baseball, Shrewsbury's Siciliano gives Bravehearts a boost
-This week heating up for Bravehearts at home. Next home game 6:30 p.m. Tuesday. Buy tickets here
-Anthony Delgreco elevated to Holy Cross women’s rowing associate head coach
-Former WPI A.D. Jim Culpepper remembered upon induction into Georgia Tech Sports Hall of Fame
>CARS: Nissan, Ford, Chevy among over 750,000 vehicles recalled
>NATIONAL: Jeffrey Epstein didn’t have a client list, committed suicide, D.O.J. and F.B.I. say
-Death toll from catastrophic flooding surpasses 100
-Indonesia’s Mount Lewotobi Laki Laki volcano erupts, sending ash 11 miles high
>TRAGIC: Camp Mystic death total rises to 27 after devastating floods
>NEW ENGLAND: Some defendants released amid defender work shortage (2:25)
-Boy, 9, dies after medical emergency at Mass. beach
>COLLEGES: Anna Maria/Oriol offering hands-on healthcare training
>TRAVEL (brought to you by Fuller RV & Rental): Why are buildings in Iceland so colorful?
>BUSINESS: Mass. business confidence remained pessimistic in June
-Bessent teases new August 1st deadline for tariffs, says Fed chair can't cut rates
>HOMES: Real estate transfers for Sunday, July 6th
>SHOPPING: How to avoid scams during Amazon Prime Day
-What to buy and avoid shopping during Amazon Prime Day
>HEALTH: Gen Z is consuming more booze
-Scientists find drinking coffee this way may extend your life
>FOOD: McDonald's fans desperate to get these discontinued items back
>TV/STREAMING: "South Park" creators rip Skydance-Paramount merger, blame deal for delaying new season
>CELEBRITY: Michael Douglas, 80, reveals why he "purposefully" quit acting
>ANIMALS: Duck loves to go swimming with her favorite cow (2:31)
>HISTORY: Then & Now: Do you know where this is?
>GOOD NEWS: Community honors beloved carhop who worked at Sonic for 40 years
-Meanwhile, Florida Man broke into home, ran bath and cooked dinner to escape angry wife
Latest obituaries | | Monday's Highlights | | Today's horoscope | | Local Sports
Quick Links: Personalize your news | | Browse members | | Advertise | | Blogs | | Invite friends | | Videos
Animals | | Boston Sports | | Business | | Cars | | Celebrity | | Colleges | | Commute & Travel | | Crime | | Faith | | Food | | Good News | | Health | | Help Wanted | History | | Homes | | Local Sports | | Lottery | | Movies | | National | | New England | | Politics | | Shopping & Deals | | SHOWTIME! | | TV & Streaming | | Weather