What Are Your Chances of Getting COVID After Being Vaccinated?

What are your chances of getting coronavirus if you're fully vaccinated?

According to medical experts, so-called breakthrough cases - cases where fully vaccinated individuals test positive for coronavirus - are possible, but have so far been rare.

The Illinois Department of Public Health has reported 56 deaths due to COVID-19 or related complications in fully vaccinated individuals since Jan. 1, but further details on those cases aren't available. As of April 28, another 183 "breakthrough" vaccine cases - those who test positive for coronavirus at least two weeks after their final vaccine dose - had been hospitalized.

That's out of more than 4.6 million fully vaccinated residents, according to state data.

Chicago's top doctor said earlier this month that the city's rate of infection post-vaccination was low, with 0.06% of fully vaccinated people contracting the virus.

"We've had more than 700,000 Chicagoans that are have a completed vaccine series - two weeks post their second dose, or two weeks post their first dose if they got J&J," Chicago Department of Public Health Commissioner Dr. Allison Arwady said last week. "And at this point we've identified fewer than 500 breakthrough cases so that's, you know, 0.06% of those who had a completed series."

She noted that a majority of the cases were asymptomatic, but as of May 5, the city had seen 48 people hospitalized with COVID-19 post-vaccination and a total of five deaths.

"We're still looking at the cause of some of these, but I can tell you folks mostly were older, no surprise," Arwady said.

Chicago's data indicated the median age for fully-vaccinated people being hospitalized with COVID-19 was 72, with cases ranging from 24 years old to 97 years old. All five deaths were also reported in people over the age of 50.

While the vaccine itself cannot give you the virus, it is also not 100% effective at preventing the virus entirely, though those who receive the vaccine are far less likely to be hospitalized or die from it, data shows.

According to the CDC, data from a multistate network of U.S. hospitals from January through March, showed the Pfizer-BioNTech or Moderna COVID-19 vaccines were 94% effective against COVID-19 hospitalization among fully vaccinated adults and 64% effective among partially vaccinated adults 65 years and older.

The CDC reports J&J/Janssen vaccine was 66.3% effective in clinical trials at preventing COVID-19 illness in people who had no evidence of prior infection 2 weeks after receiving the vaccine.

Health experts have expressed concern about new and emerging variants of the virus. Though studies have shown the current vaccines provide protection against known variants so far, they may not be as effective against the new strains.

"Every single time someone is diagnosed with COVID we're looking behind the scenes to say, 'Were they actually fully vaccinated' and if they were fully vaccinated that would meet the definition of a breakthrough case. And then we're working to try to get that lab sample to check and see is it related to a variant?" Arwady said.

According to Arwady, however, data has so far not pointed to variants being responsible for a majority of breakthrough cases in Chicago.

Still, boosters and new versions of vaccines that target the variants are already being explored.

Pfizer-BioNTech is testing a third booster shot of its vaccine on fully vaccinated people.  

"The flexibility of our proprietary mRNA vaccine platform allows us to technically develop booster vaccines within weeks, if needed," Ugur Sahin, CEO and co-founder of BioNTech, said in a release.

Moderna is also testing a potential third dose of its current vaccine, and a possible booster shot specifically targeting the South Africa variant. Citing early data, the company recently said the booster vaccine generated a promising immune response against the B.1.351 and P.1 variants first identified in South Africa and Brazil, respectively.

Meanwhile, Johnson & Johnson CEO Alex Gorsky said during an interview with CNBC's "Squawk Box" in March that the company is well-positioned to adapt its vaccine for variants, and is working on developing software that will "help address some of these new and emerging variants."

The recent death of a suburban Chicago father with leukemia, who contracted COVID despite being fully-vaccinated, has raised some questions about vaccine efficacy in immunosuppressed individuals.

Current CDC guidelines indicate those with compromised immune systems should receive the vaccine, however, they should "be aware of the potential for reduced immune responses to the vaccine."

"I think there's still ongoing work about you know how well it works in people who are immunocompromised, but I think it's an important thing to still be vaccinated because you're still getting, you know, some level of protection from that vaccination," Dr. Candice Robinson, medical director for CDPH, said in a Facebook Live last week.

Arwady acknowledged cases where some immunocompromised individuals have shown lower antibody levels post-vaccination, but said the vaccine could still provide some level of protection that would benefit those people.

"It's not that there's a problem with someone who is immunocompromised getting vaccinated. Usually, you know, like Dr. Robinson said, you 100% should get vaccinated, but there may be in people who, you know, are immunocompromised, and especially more severely immunocompromised... you may not get as high a level of protection," Arwady said. "So it's definitely been seen and for people who are seriously immunosuppressed it's a discussion you should have with your doctor."

The Leukemia & Lymphoma Society, citing data from a recent U.K. study, reports that "some blood cancer patients may not get optimal protection from the vaccines and may be more susceptible to COVID-19 infections after vaccination compared to the general public."

In that study from King’s College London, data showed that three weeks after one dose of the Pfizer vaccine, an antibody response was found in 39% of solid cancer patients and just 13% of people with blood cancer, compared to 95% in healthy individuals, the society reported.

The group urged blood cancer patients to continue wearing masks and taking preventative measures like social distancing and handwashing.

Similarly, a recent study from the University of Pittsburgh Medical Center found that "people with cancer that affects the blood, bone marrow or lymph nodes are at elevated risk of COVID-19 vaccine failure, particularly those with chronic lymphocytic leukemia."

The study tested blood from 67 patients with "hematologic malignancies" who had been vaccinated with either the Pfizer or Moderna COVID-19 two-dose vaccines three weeks earlier. The tests found that more than 46% of the participants had not produced antibodies against COVID-19 and only three in 13 patients with chronic lymphocytic leukemia had produced measurable antibodies, even though 70% of them weren’t undergoing any form of cancer therapy. 

“As we see more national guidance allowing for unmasked gatherings among vaccinated people, clinicians should counsel their immunocompromised patients about the possibility that COVID-19 vaccines may not fully protect them against SARS-CoV-2,” the study's senior author Dr. Ghady Haidar, a transplant infectious diseases physician and assistant professor in the university's Department of Infectious Diseases, said in a statement. “Our results show that the odds of the vaccine producing an antibody response in people with hematologic malignancies are the equivalent of a coin flip.”

According to Haidar, however, a negative antibody test does not necessarily mean a patient isn't protected from the virus.

Many medications and treatments for certain cancers or other conditions can cause immune suppression or weaken an immune system.

The University of Chicago wrote in a blog post in February that there is little-to-no data surrounding the coronavirus vaccines' effectiveness in immunocompromised people because they weren't included in the vaccines' initial trials.

"Researchers don’t know whether these immunosuppressant treatments make the Pfizer and Moderna vaccines less effective – as some do in the case of flu vaccines – or if pausing or delaying treatment could make the vaccines work better. But it’s important that patients not change their treatment schedule without first speaking to their doctor," the university's post read.

With little data to offer, the Leukemia & Lymphoma Society is asking those living with blood cancers to register to become a "citizen scientist" and share their experiences with COVID-19 and the vaccines currently available.

The CDC said those with compromised immune systems should continue following the public health guidelines after vaccination.

Arwady noted that others getting vaccinated will also help to protect those with compromised immune systems.

"To take this one step farther, I think where someone who you know is seriously immunocompromised, they're gonna get vaccinated, but still, where there's a lot of COVID around that could be a setting where if, you know, they really want to make sure everybody who's in close touch with them is fully vaccinated, right?" she said. "It's just, it becomes extra important and probably taking some more care with masks, etc."

And that could extend beyond immunosuppressed individuals.

Arwady had previously said the risk of contracting COVID after vaccination will decrease as more people get vaccinated.

"As our case numbers go down, as we really sort of get past COVID, the chance that you will be exposed to COVID will be even lower and this won't be as much of a concern," she said last month.

Still, examples of breakthrough cases have been reported.

Ariel Silver of Northbrook, a sales manager for a medical device company, said she received her second dose of the Pfizer vaccine in mid-January and tested positive for COVID-19 in early March.

“Having been fully vaccinated for six weeks and then to get a positive COVID test, I was shocked,” Silver said.

Silver said her two young daughters tested positive in late February, and soon after she started feeling sick.

“It hit me hard," she said. "I’ve read that if someone vaccinated gets COVID, it’s usual very mild symptoms. But for two days my symptoms were not mild at all. I was in bed, very ill."