These 7 Conditions Make the Pfizer Vaccine Less Effective, New Study Says

The vaccine is still protective for certain subgroups, just at a lower efficacy rate.

The COVID vaccines authorized for emergency use in the U.S. have proven to be highly effective in protecting against symptomatic and severe COVID. While these vaccines are more effective than rates we usually see for something like the flu vaccine, "no vaccine prevents illness 100 percent of the time," the Centers for Disease Control and Prevention (CDC) explains. So it's important to know if there is anything that could possibly make the vaccine less effective for you. The Pfizer vaccine is 96 percent effective against symptomatic COVID and 95 percent effective against severe COVID for the general population, according to a new large real-world COVID study by the Clalit Research Institute in collaboration with Harvard University. However, the results—which were recently published in New England Journal of Medicine—also indicate that seven common conditions can make the Pfizer vaccine slightly less effective (although still more than effective enough to protect you). Read on to find out if you are in an affected subgroup and for more on this specific vaccine, Pfizer's CEO Just Said How Often You'll Need a COVID Vaccine.


A senior man is at home by the window, he is wearing a protective face

People with immunodeficiencies are usually told to avoid getting vaccines that contain live virus, but the COVID vaccines do not, making them safe for this group. However, because immunosuppressed or immunocompromised individuals have a weakened ability to fight off infections, some people with immunodeficiencies, like those getting treated for cancer or who have HIV, were concerned.

"As vaccines work by mobilizing our immune systems, for people who have a weaker immune system to begin with, vaccines may not be as effective. They may generate an incomplete or short-lived response, so people with immunodeficiencies may need additional boosters to maintain protective immunity," immunologists Vanessa Bryant, PhD, and Charlotte Slade, PhD, of Walter and Eliza Hall Institute in Australia, wrote for The Conversation.

People with primary immunodeficiencies or cancer weren't included in clinical trials and only a very small number of people with HIV were, so the Clalit Research Institute study provides some of the first data we have on how well the vaccine works for immunodeficient people. And it's very good news. According to the findings, the Pfizer vaccine is 84 percent effective in preventing symptomatic COVID cases for immunosuppressed or immunocompromised individuals. The vaccine is also 100 percent effective in protecting immunosuppressed individuals from being hospitalized for COVID or developing severe COVID.

And for more on getting COVID after the vaccine, 65 Percent of Vaccinated People Who Get COVID Have This in Common, CDC Says.

Heart disease

Portrait of a beautiful woman with surgical mask and hands on her heart sending love to family and friends during covid19 coronavirus pandemic

People with heart disease are some of the most at risk for severe cases of COVID. A Dec. 2020 meta-analysis published in the British Medical Journal found that cardiovascular disease (CVD) was "closely related to fatal outcomes in COVID-19 for patients across all ages." That's why people with this comorbidity were prioritized to get the vaccine early in the rollout process. And though it's slightly less effective for those with heart disease than it is for those without, the Clalit Research Institute findings show that the Pfizer vaccine is 80 percent effective against symptomatic COVID infection for people with CVD. It's even more effective at protecting against severe disease in these individuals: It's 89 percent effective against hospitalization for COVID and 97 percent effective against severe COVID for those with CVD.

Chronic kidney disease

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Those living with kidney disease are at a high-risk for severe COVID, like the other conditions on this list—which is why getting vaccinated is particularly important. "Most doctors agree that the benefits of the COVID-19 vaccine for people with kidney disease at any stage, including those on dialysis and those with a kidney transplant, are much greater than the risk of serious complications from the virus than from the vaccine," the National Kidney Foundation writes.

In a Feb. 2021 paper published in the Nature Reviews Nephrology, a group of doctors from Austria, Sweden, Germany, the U.S., Singapore, Canada, and the U.K. noted that "vaccine responses are likely to be lower in patients with kidney diseases than in the general population." And while that appears to be true, based on the Clalit Research Institute study, it's not by much. If you have chronic kidney disease, the Pfizer vaccine is 80 percent effective against symptomatic COVID infection. It's also 76 percent effective against hospitalization and 74 percent effective against severe COVID.

And for more on the vaccine, This One Vaccine May Protect You Against All Variants, New Study Says.


woman with diabetes checking her blood sugar

Throughout the pandemic, those with type 2 diabetes have been particularly at risk for severe COVID and death due to the virus. A May 2020 study found that one in ten people who have diabetes and develop COVID die within seven days of being admitted to the hospital. That is precisely why it was important for thousands of people with diabetes to be included in the clinical trials for the Pfizer, Moderna, and Johnson & Johnson vaccines. Though there wasn't data specifically on how the vaccine protected this group, it did prove to be safe. Doctors like Robert Gabbay, MD, PhD, chief science and medical officer for the American Diabetes Association (ADA) in Arlington, Virginia, advise that "people with diabetes get vaccinated as soon as it becomes available to them," as he told Everyday Health.

While COVID may be particularly fatal for people with type 2 diabetes, the Pfizer vaccine protects this group rather well, the new Clalit Research Institute study shows. For people with diabetes, the vaccine is 86 percent effective against symptomatic COVID, 85 percent effective against hospitalization for COVID, and 91 percent effective against severe COVID. And for more up-to-date COVID news delivered right to your inbox, sign up for our daily newsletter.


Photo of man preparatio checking blood presure at home

People with high blood pressure are another high-risk group. As the CDC states, "high blood pressure (hypertension) can make you more likely to get severely ill from COVID-19." Those with hypertension were also included in the COVID vaccine trials, and they were deemed safe for people with the condition.

"If you're taking medication for high blood pressure, you should still get the COVID-19 vaccine. In fact, it's very important for people with high blood pressure," note the doctors at Jackson Care Connect in Medford, Oregon.

The good news is, hypertension only lowers the efficacy of Pfizer's vaccine by a few notches, the Clalit Research Institute found. It's 90 percent effective at preventing symptomatic COVID in people with hypertension, and 94 and 93 percent effective against hospitalization and severe disease, respectively.

And if you're signed up to get the shot, know that Pfizer's Vaccine Protects You for at Least This Long, Study Finds.

Cerebrovascular disease

radiologist in uniform and protective mask looking at x-ray image of patient lying on long couchette of medical equipment

Cerebrovascular disease is an umbrella term for a range of conditions that affect your blood flow to your brain, including stroke and aneurysms. Again, people who've had strokes are at an increased risk of severe COVID, so the vaccine is all the more important for this group. "Stroke survivors should get vaccinated as soon as possible because they are at much greater risk from the virus than they are from the vaccine," the American Heart Association warns.

"If you've had a stroke in the past, these vaccines may reduce your chances of getting the severe form of COVID-19 disease. If you get COVID-19 infection, it can cause your body's natural inflammation pathways to heighten. This can cause your blood to become thick, and especially in stroke patients, it can lead to even more neurological complications, including new strokes," Shazam Hussain, MD, and Pravin George, DO, wrote for U.S. News & World Report.

The efficacy of the Pfizer vaccine against symptomatic COVID saw the largest reduction among those with cerebrovascular disease, according to the Clalit Research Institute. But it's still considered highly effective. If you fall into this category, know that the vaccine is 75 percent effective in preventing symptomatic COVID, 85 percent effective in preventing hospitalization, and 91 percent effective against severe COVID.

And for more on other vaccines, This Is How Much the Moderna Vaccine Really Protects You, New Study Says

Neurological disease

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Neurological diseases are any conditions that affect the brain and the nerves throughout your body and the spinal cord. Many diseases fall under this category, including dementia, Alzheimer's, multiple sclerosis, and Parkinson's. As the CDC notes, "Having neurological conditions, such as dementia, can make you more likely to get severely ill from COVID-19." A Feb. 2021 study out of the School of Medicine at Case Western Reserve University found that people with dementia are twice as likely to catch COVID than those who do not. Worse yet, the research showed that COVID patients with dementia are 2.6 times more likely to be hospitalized due to COVID and 4.4 times more likely to die from it than patients without the neurological disease.

However, the Pfizer vaccine is still quite effective for people with a neurological disease, the Clalit Research Institute study found. It's 84 percent effective against symptomatic infection, and though it's 69 percent effective against COVID hospitalization, it's 100 percent effective against severe disease. And for more on the future of COVID vaccinations, read up on how the Doctor Behind Pfizer-BioNTech Vaccine Says You'll Need a Shot This Often.

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