In mid-April, the US Centers for Disease Control and Prevention reported about 5,800 cases of COVID-19 among Americans who have completed a full course of vaccination. These so-called breakthrough cases amounted to 0.008% of more than 66 million people at least two weeks after receiving their final vaccine dose.
Among them, as many as 396 or 7% required hospitalisation. Some became seriously ill and 74 people died, the CDC informed.
«Vaccine breakthrough infections were reported among all people of all ages eligible for vaccination. However, a little over 40% of the infections were in people 60 or more years of age,» the CDC said.
Among them, 65% were female. As much as 29% of the breakthrough infections were asymptomatic.
The agency has developed a national COVID-19 vaccine breakthrough database where state health department investigators can currently enter, store, and manage data for cases in their jurisdiction.
«Vaccine breakthrough infections make up a small percentage of people who are fully vaccinated. CDC recommends that all eligible people get a COVID-19 vaccine as soon as one is available to them. CDC also continues to recommend people who have been fully vaccinated should keep taking precautions in public places, like wearing a mask, staying at least six feet apart from others, avoiding crowds and poorly ventilated spaces, and washing their hands often.»
Officials said such cases are in line with expectations because the approved vaccines in the US have efficacy levels below 100%.
The agency said it was monitoring reported cases for clustering by patient demographics, geographic location, and time since vaccination, vaccine type or lot number, and SARS-CoV-2 lineage. This is the CDC›s first public accounting of breakthrough cases.
CDC has a small team studying breakthrough cases. One question the researchers are considering is whether particular variants of the coronavirus might play a role in breakthrough cases.
Importantly, samples from cases will be tested to see how many are caused by variants and if so, which ones.
Currently, there is no evidence that Covid-19 is occurring after vaccination because of changes in the virus,” according to an agency spokeswoman.
Pfizer and Moderna are expected to release data in the coming months. That should indicate how often vaccinated people become infected by the virus, even if they have no symptoms. The companies have been testing participants in their vaccine trials for antibodies to a protein called N that is part of the coronavirus but not part of the vaccine. Finding those antibodies means that a vaccinated person has been infected by the virus. Nasopharyngeal swabs are also being collected from the volunteers regularly to test for an active viral infection, reports show.