RELATED: The CDC Says Vaccinated People Who Get COVID Have This in Common. According to WebMD, three things are more likely to lead to a breakthrough infection: a health care worker accidentally storing or giving you the vaccine incorrectly, having a weakened immune system, or catching a COVID variant. A report released April 22 by the Institute for Safe Medication Practices (ISMP) analyzed around 160 COVID vaccine errors voluntarily reported between Dec. 14 and April 15, but ISMP said this does “not reflect all COVID-19 vaccine errors that may be occurring nationally.” The most common errors included giving too low or too high of a dose, administering the wrong vaccine for a second dose, using the wrong injection technique or needle size, or improper vaccine storage and handling. If there was an administration error with your vaccine, the CDC requires that health care officials contact you.ae0fcc31ae342fd3a1346ebb1f342fcb In terms of having a weakened immune system, many recent studies have shown that this causes the vaccines to produce fewer antibodies. A May 5 study from the John Hopkins University School of Medicine found that only 17 percent of organ transplant recipients had antibodies after the first COVID vaccine dose, and that number increased to just 35 percent after two doses. “There may be some immunosuppressed patients who got vaccinated and have adequate protection and there may be some who don’t,” Amesh A. Adalja, MD, a senior scholar at Johns Hopkins Center for Health Security, told CreakyJoints. “We are in the infancy of understanding what the correlate of protection may be for COVID-19 post-vaccination.” RELATED: For more up-to-date information, sign up for our daily newsletter. And then there are the variants, including the highly infectious Delta variant that’s spreading throughout the U.S. A May 22 study from Public Health England found that Pfizer’s vaccine efficacy against symptomatic COVID dropped to just 33 percent after one dose and 88 percent after two doses against the Delta variant. The vaccine is generally 95 percent effective against symptomatic COVID after two doses, per the CDC. White House COVID adviser Anthony Fauci, MD, said that the prevalence of the Delta variant has doubled in the U.S. over the last two weeks, with it now being responsible for one in every five current COVID cases in the country. “The Delta variant is currently the greatest threat in the U.S. to our attempt to eliminate COVID-19,” Fauci said during a White House COVID briefing on June 22. Los Angeles County, in accordance with new recommendations from the World Health Organization (WHO), has asked fully vaccinated individuals to mask back up indoors for the time being. “Until we better understand how and to who the Delta variant is spreading, everyone should focus on maximum protection with minimum interruption to routine as all businesses operate without other restrictions, like physical distancing and capacity limits,” an L.A. County official wrote in a statement. RELATED: 3 in 4 Fully Vaccinated People Who Get Severe COVID Have This in Common.