During pregnancy, immune defenses shift instead of drop across the board; risks rise for flu, COVID-19, and some foodborne germs.
Searchers ask for a number, but there isn’t a single percentage that fits every arm of defense. Pregnancy changes both innate and adaptive responses in different ways. Some arms turn up, some settle down, and the mix changes by stage. The result: susceptibility to a few infections rises, while day-to-day protection against routine microbes still works for most people.
What Changes Week By Week?
The body builds tolerance to the fetus without dropping its guard against threats. Neutrophils and monocytes often climb, pattern-recognition signaling stays busy, and antibody work keeps going. T cell activity tilts toward anti-inflammatory cues in mid-pregnancy, then shifts again near delivery. That ebb and flow helps maintain a healthy pregnancy while still fighting germs.
| Stage | Typical Immune Pattern | What It Means Day To Day |
|---|---|---|
| First Trimester | Tissue-healing signals rise; some cell-mediated responses cool | More fatigue; watch food safety and hand hygiene |
| Second Trimester | Anti-inflammatory bias peaks; innate cells stay active | Generally stable; stay on vaccine schedule when due |
| Third Trimester | Inflammatory readiness ramps back up for labor | Respiratory bugs can hit harder; flu and COVID-19 need fast care |
| Early Postpartum | Gradual reset toward pre-pregnancy | Keep illness precautions; rest and hydration matter |
How Much Does Immunity Change In Pregnancy? Evidence And Ranges
Studies show higher rates of severe outcomes for certain infections during this time. Respiratory viruses lead the list. Influenza carries greater odds of hospital care, and COVID-19 carries higher risk of intensive care and breathing support compared with the same person outside pregnancy. Foodborne germs such as Listeria deserve added caution because even mild tummy upset in the parent can threaten the baby.
There is no universal “drop by X percent.” Innate defenses like neutrophils often rise, while some T cell responses lean away from aggressive attack in mid-pregnancy. Antibody production continues, and vaccines still work well. Think of the system as retuned instead of weakened.
Why Risk Rises For Specific Infections
Two drivers stand out. First, biology: the immune profile prioritizes tolerance to protect the fetus. Second, physiology: the heart works harder, the diaphragm sits higher, and lung capacity shifts, which can make respiratory illness tougher. Add exposures at work or at home, and the risk picture varies person to person.
Respiratory Viruses
Flu seasons routinely show higher odds of hospital care for people who are expecting. Vaccine protection cuts that risk and also helps the newborn during early months. Public health groups advise an annual flu shot during the season because circulation patterns shift year to year.
Coronaviruses
COVID-19 risk includes higher chances of intensive care, ventilation, and complications in late pregnancy and the period right after birth. Baseline health, age, and exposures shape the odds. Vaccination lowers risk of severe outcomes and helps provide passive antibodies in the baby after delivery.
Foodborne Germs
Listeria can cross the placenta. Avoid unpasteurized dairy, deli meats that aren’t heated, and refrigerated smoked seafood. Wash produce well, keep fridge temps cold, and toss leftovers on time.
Myths And Realities About “Lowered Immunity”
It is common to hear that people become “immunosuppressed” during this time. That label does not match modern data. The system does not shut off; it adjusts. Innate responses often increase. Some T cell functions cool in the middle third, then rev again near delivery. Antibody responses remain effective, which is why shots work and protect newborns through transferred antibodies. This retuning is targeted, not blanket weakness.
Another common belief is that illness is inevitable. Risk is higher for a few infections, but most days pass without trouble. Habits, vaccines, and quick treatment close much of the gap between this stage of life and any other time.
What You Can Do Right Now
Simple steps pay off. Wash hands often, clean high-touch surfaces, and keep distance from people who are sick. Sleep enough, stay active as cleared by your clinician, and eat a varied, fiber-rich diet. Keep every prenatal visit. Ask your care team about timing for flu, Tdap, and up-to-date COVID-19 vaccination. These steps protect both you and the baby.
If You Get Sick: Step-By-Step Plan
- Check symptoms and temperature. Note onset time and any shortness of breath.
- Call your clinician’s office early in the day. Mention that you are pregnant and list exposures.
- Test for COVID-19 or flu if your care team advises. Antivirals work best early.
- Drink fluids. Aim for pale urine. Use oral rehydration salts if nausea limits intake.
- Use approved fever reducers as directed by your clinician. Avoid new meds without guidance.
- Rest, isolate when needed, and wear a mask around household contacts.
- Seek urgent care for breathing trouble, chest pain, blue lips, confusion, or fewer fetal movements.
Everyday Risk Management At Home
Food Safety Moves
Heat deli meats until steaming, skip raw milk cheeses, and chill leftovers within two hours. Keep the refrigerator at 4 °C/40 °F or colder. Use a separate cutting board for raw meat and wash tools with hot, soapy water.
Air And Crowds
During peak respiratory season, lean on well-ventilated spaces and masks in packed indoor settings. Keep a small bottle of hand rub handy. If a partner or child is sick, use separate towels and sanitize shared surfaces.
Work And Travel
Ask about flexible duties during heavy flu activity. For flights, sit near a vent, wipe surfaces, and drink water. Pack meds cleared by your clinician, including fever reducers and oral rehydration salts.
Who Faces Higher Risk?
Risk climbs with age over 35, higher body mass index, diabetes, lung disease, heart disease, kidney disease, and immune-affecting medications. Work that brings close contact with crowds or sick people adds exposure. Living conditions and air quality play a part. Tell your clinician about these factors so your care plan fits your life.
Clinician-Backed Vaccines And Timing
Two shots carry routine timing in many settings: the seasonal flu shot during flu season, and Tdap in the late second or early third trimester to pass antibodies against pertussis. COVID-19 vaccination follows current public health schedules. Your care team may raise RSV vaccination during specific weeks for added infant protection in eligible regions. Local schedules vary, so follow regional guidance.
| Vaccine | When Given | Main Goal |
|---|---|---|
| Influenza (IIV or RIV) | Any trimester during flu season | Lower severe flu in parent; protect infant early on |
| Tdap | 27–36 weeks, each pregnancy | Boost antibodies for newborn pertussis protection |
| COVID-19 | As due per regional schedule | Cut risk of severe disease and ICU care |
Trimester-By-Trimester Checklist
First Trimester
- Set vaccine plans with your clinician based on season and region.
- Tune food safety habits and fridge temps.
- Review meds and supplements for safety and dosing.
Second Trimester
- Schedule Tdap for weeks 27–36.
- Plan travel with contingency space for rest and hydration.
- Recheck chronic condition plans and devices like inhalers.
Third Trimester
- Keep distance from people with coughs or fevers.
- Line up help at home to allow recovery time if illness hits.
- Know the fastest route to urgent care or labor and delivery.
When Numbers Help, And When They Don’t
Readers love tidy figures, but immune change is not a single dial. One study may report a rise or dip for a cell type or cytokine at a given week, then the pattern shifts later. Real-world risk shows up more clearly in outcomes: higher odds of hospital care for flu, and higher odds of intensive care for COVID-19. Those trends guide vaccine and treatment plans.
Talking With Your Care Team
Share your work setting, household exposures, and any chronic conditions. Ask which symptoms should trigger a same-day visit and which can start with phone triage. Clarify which meds you can take for fever, cough, or nausea. Keep a list on your phone.
Evidence-Based Reading
You can read public health pages for plain-language guidance. The CDC flu and pregnancy page explains who needs a shot and why. For COVID-19 risk and clinical points in pregnancy and the period after birth, see the CDC page on special populations. These sources summarize data behind the care steps in this article.
Treatment Windows And Safety Notes
Antivirals for flu work best when started early. If your clinician suspects flu based on symptoms and local activity, treatment may start the same day without waiting for a swab. That fast start shortens illness and lowers the chance of complications. For COVID-19, your team will weigh timing, interactions, kidney function, and local guidance. Bring an up-to-date med list to visits so choices are clear.
With stomach bugs, fluids come first. Use small, steady sips, chilled if that sits better. If you can’t keep liquids down, or you pass less urine than usual, call. Avoid bismuth products unless your clinician says they are safe for you. With any new rash, especially with fever, ask for a same-day review.
After Birth: The First Six Weeks
The risk profile does not reset overnight. Respiratory illness can still run hard during the first weeks after delivery, and fatigue makes recovery slower. Keep masks and hand rub within reach at home and during newborn visits. Anyone who wants to hold the baby should wash hands first. If you feel short of breath, have chest pain, or spikes of fever, seek care the same day. Share any postpartum bleeding concerns as well; dehydration can worsen symptoms.
Bottom Line For Daily Life
Immune defenses are tuned, not shut down. Some infections pose higher stakes, especially respiratory viruses and certain foodborne germs. Smart habits, timely shots, and early care shift the odds in your favor while protecting the baby. Treat the next weeks as a season of extra care and quick action when sick, and lean on your clinical team for region-specific steps.