Of the more than 130m people in the US who have been fully vaccinated against COVID-19, there have been reports of some 10,000 breakthrough infections, reports the Centers for Disease Control and Prevention.
The CDC has stopped investigating breakthrough infections among fully vaccinated people unless they become so sick that they are hospitalised or die.
A breakthrough infection occurs when someone tests positive for coronavirus more than 14 days after the second dose of the Pfizer-BioNTech or Moderna vaccines or the single Johnson & Johnson shot, writes NBC News. Roughly a quarter of the breakthrough cases didn’t have symptoms and were likely detected through routine testing. Of 955 people who were hospitalised, about a third were in the hospital for reasons unrelated to Covid-19, or were asymptomatic. About 160 people, or 2%, died. Twenty eight of the deaths were unrelated to Covid-19. The CDC didn’t report whether the people had comorbidities .
The majority of the breakthrough infections were women, 63%, and a majority were 40-74 years old.
The CDC report cautions, however, that these cases are likely an underestimate because most people who have been fully vaccinated aren't being regularly tested. Recently, the CDC said that, with some exceptions, people who are fully vaccinated don’t need a coronavirus test, even if they’ve been exposed to the virus, unless they show symptoms.
On May 1, the CDC stopped regularly reporting on mild breakthrough infections so it could focus on investigating only cases severe enough to cause hospitalisation or death. However, it's still working with local governments to understand whether variants are linked to infections after vaccination.
Through genomic sequencing, the CDC found that several variants of concern played a role in most of the breakthrough cases. The B.1.1.7 variant first identified in the UK was linked to 57% of cases, and a quarter were due to the B.1.429, first found in California. A small percentage of sequenced cases were caused by the P.1 from Brazil and the B.1.315 first identified in South Africa.