Most people can safely receive vaccines, but there are specific groups who should skip certain shots or delay them. The reasons fall into a few clear categories: severe allergic reactions to vaccine ingredients, weakened immune systems, pregnancy (for certain vaccines), and being too young. Very few of these are permanent. Most are temporary, meaning you can get vaccinated once the condition resolves.
Severe Allergic Reactions to Vaccine Ingredients
If you’ve ever had a severe allergic reaction (anaphylaxis) after a vaccine dose, you should not receive another dose of that same vaccine. This is the most universal contraindication across all vaccines. The reaction doesn’t have to be to the active ingredient itself. Vaccines contain stabilizers, preservatives, and residual manufacturing compounds that can trigger allergies in rare cases.
Gelatin is one of the most common culprits. It’s used as a stabilizer in several vaccines, including MMR (measles, mumps, rubella) and varicella (chickenpox). About one-third of patients who had allergic reactions to certain pertussis vaccines showed antibodies against gelatin. Polyethylene glycol (PEG), a compound found in mRNA COVID vaccines and many everyday products, has also been linked to anaphylaxis in people with a known PEG allergy. Polysorbate 80, used in other vaccines, can cause similar reactions in isolated cases.
One allergy that no longer disqualifies you: egg allergy. For years, people with severe egg allergies were told to avoid the flu shot or get it under special observation. That’s changed. As of the 2023-2024 flu season, the CDC no longer recommends any extra safety measures for people with egg allergies beyond what applies to every vaccine recipient. You can receive any flu vaccine, egg-based or not, regardless of how severe your egg reaction has been. The only standard precaution is that all vaccines should be given in a setting equipped to handle allergic reactions, which is true for everyone.
People With Weakened Immune Systems
Live vaccines are the main concern here. Unlike inactivated vaccines, which contain killed or partial versions of a germ, live vaccines use a weakened but still active form of the virus or bacteria. In a healthy person, the weakened germ triggers an immune response without causing disease. In someone with a significantly compromised immune system, however, that weakened germ can multiply unchecked and cause serious illness.
The live vaccines that are typically off-limits include MMR, varicella, the nasal spray flu vaccine, yellow fever, oral typhoid, BCG (tuberculosis), smallpox, and rotavirus. Inactivated vaccines are generally safe for immunocompromised people, though they may not work as well.
The level of immune suppression matters. People with severe combined immunodeficiency (SCID), complete DiGeorge syndrome, or other major defects in cellular immunity should avoid all live vaccines. Those with partial immune deficiencies, like Wiskott-Aldrich syndrome, also fall into this category. Certain rare conditions affecting specific immune pathways, such as deficiencies in interferon production, rule out both live viral and live bacterial vaccines. People with defects in the cells that fight bacteria directly (phagocytic function) should not receive live bacterial vaccines specifically.
If your immune system is temporarily suppressed, say from chemotherapy, high-dose steroids, or medications for an autoimmune condition, live vaccines are typically deferred until immune function recovers. Your doctor can help determine the right timing based on your treatment timeline.
Pregnancy and Live Vaccines
Pregnant women should not receive live attenuated vaccines, including MMR and varicella. The concern is theoretical: a live virus in the vaccine could potentially cross the placenta and affect the developing fetus. The nasal spray flu vaccine is also live and should be avoided during pregnancy. The standard injectable flu shot, which is inactivated, is recommended during pregnancy and is considered safe.
Some vaccines are specifically recommended during pregnancy, including the flu shot, the Tdap (tetanus, diphtheria, pertussis) vaccine, and the RSV vaccine. These are inactivated and provide protection to both the mother and the newborn. If you’re due for an MMR or varicella vaccine, the guidance is to get it either before becoming pregnant or after delivery.
Infants Below Minimum Age
Every vaccine has a minimum age, and giving it earlier than that can be either ineffective or unsafe. Hepatitis B is the earliest, given at birth. Rotavirus starts at one to two months. Most other childhood vaccines begin at two months. MMR and varicella aren’t given until 12 months, because maternal antibodies circulating in the baby’s blood during the first year can interfere with the vaccine’s ability to produce a strong immune response.
These age cutoffs aren’t arbitrary. They’re based on when a child’s immune system is mature enough to respond to each specific vaccine and when the risk-benefit calculation favors vaccination.
Previous Serious Reactions to a Specific Vaccine
Two specific past reactions serve as clear stop signs. First, if you experienced anaphylaxis after a dose of any vaccine, you should not receive that vaccine again (or any vaccine containing the ingredient that triggered the reaction). Second, if a child developed encephalopathy (brain swelling) within seven days of receiving a pertussis-containing vaccine, with no other identifiable cause, they should not receive any further doses containing pertussis.
For RSV vaccines specifically, the FDA has required warnings about an increased risk of Guillain-Barré syndrome, a rare nerve disorder causing muscle weakness, within the 42 days following vaccination. This applies to the adult RSV vaccines currently available. While this is listed as a warning rather than an absolute contraindication, it’s an important consideration if you have a history of Guillain-Barré syndrome.
Temporary Reasons to Delay
If you’re moderately or severely ill, with or without a fever, vaccination is typically postponed until you recover. This isn’t because the vaccine is dangerous during illness, but because your immune system is already occupied, which can reduce the vaccine’s effectiveness and make it harder to distinguish vaccine side effects from symptoms of your illness.
Mild illness, even with a low-grade fever, is not a reason to delay vaccination. A runny nose, a mild ear infection, or a course of antibiotics does not interfere with how vaccines work.
Conditions That Are Not Reasons to Skip Vaccines
A surprising number of people miss vaccines based on conditions that sound like they should matter but don’t. None of the following are valid reasons to skip or delay vaccination:
- Mild local reactions to a previous dose, such as swelling, redness, or soreness at the injection site
- Low-grade fever after a previous dose
- Family history of seizures or adverse vaccine reactions
- Penicillin allergy or other non-vaccine allergies
- Receiving allergy shots (allergen immunotherapy)
- Mild acute illness with or without fever
These are sometimes called “false contraindications,” and they’re one of the most common reasons people end up under-vaccinated. A sore arm after your last flu shot, or the fact that your parent had a bad reaction to a vaccine, does not put you at higher risk. If you’ve been told you can’t get vaccinated for one of these reasons, it’s worth revisiting the question.