The Centers for Disease Control and Prevention (CDC) reported more than 10,000 post-vaccination COVID-19 cases. These so-called breakthrough cases came from 46 U.S. states and territories that sent figures to the public health agency. The CDC’s report came as about 101 million Americans became fully vaccinated as of April 30.

According to CDC data as of April 30, there were 10,262 breakthrough infections reported in fully vaccinated people. Breakthrough cases are defined as Wuhan coronavirus infections that occur two or more weeks after someone gets their final COVID-19 vaccine dose. This can refer to the second dose of the Pfizer/BioNTech or Moderna mRNA vaccine or the single-dose Johnson & Johnson vaccine.

Approximately 10 percent of the 10,262 patients required hospital care. About 1.5 percent – equal to 160 persons – died of COVID-19. Meanwhile, about three in 10 hospitalized patients did not show symptoms or were admitted for a reason unrelated to COVID-19. Twenty-eight deaths were noted in asymptomatic patients or attributed to causes unrelated to the disease.

The public health agency said the latest figures indicate that breakthrough infections occur in just “a small fraction” of vaccinated persons. It continued: “The number of COVID-19 cases, hospitalizations and deaths that will be prevented among vaccinated persons will far exceed the number of vaccine breakthrough cases.”

The CDC noted two limitations to the figures it released. First, the number of vaccine breakthrough cases may be a “substantial undercount” as its surveillance system for these reports relies on passive and voluntary reporting. Second, many people with breakthrough infections – particularly asymptomatic patients – might not seek testing.

The agency nevertheless insisted that there is no evidence the COVID-19 vaccines contributed to patient deaths. “Reports to the [Vaccine Adverse Event Reporting System] of death following vaccination do not necessarily mean the vaccine caused the death,” a post on its website said. 

The vaccines themselves increase people’s risk of contracting Wuhan coronavirus variants of concern

Of the more than 10,000 breakthrough infection reports the CDC received, more than 500 cases had genomic sequencing data available. Wuhan coronavirus variants, including the British B117 strain, were responsible for over 60 percent of these 555 breakthrough infections.

The CDC’s findings came out on the same day that a separate group of researchers released a study about breakthrough infections. University of Washington scientists noted in their May 2021 paper that variants of concern are “over-represented” among the breakthrough cases they examined. Of the 20 cases investigated, the B1427 strain – one of two variants first found in California – was responsible for 40 percent of infections.

They noted that variants known for reduced antibody neutralization – such as the California B1427 and B1429 strains, the South African B1351 strain and the Brazilian P1 strain – were over-represented vis-à-vis the B117 strain. They also found that the 20 breakthrough cases they observed had a substantially stronger viral load than usual.

Despite the reports of post-vaccination infections, the CDC is working on clinical studies to examine the effectiveness of current COVID-19 vaccines. It will also continue collecting information on breakthrough infections.

Brown University School of Public Health Dean Dr. Ashish Jha said the CDC’s report shows that the three COVID-19 vaccines authorized for emergency use in the U.S. work well. He said during an ABC appearance: “These vaccines are way better than I would have predicted a year ago. But they’re not 100 percent [effective], so … we’re going so see some breakthrough infections [that are] exceedingly rare.”

A study in the middle of April this year showed how vaccines may put people at a higher risk of contracting Wuhan coronavirus variants of concern. Israeli researchers examined COVID-19 test results of both unvaccinated people and those who received the Pfizer/BioNTech vaccine. Israel used the two-dose mRNA vaccine on the majority of its population.

They then compared the test results from both groups and found that individuals fully vaccinated with the Pfizer/BioNTech COVID-19 vaccine were eight times more likely to contract the B1351 variant. Meanwhile, those who received at least one dose had a higher chance of contracting the B117 variant. The prevalence of the British strain was no different in Israelis who were fully vaccinated, the researchers found.

Lead researcher Dr. Adi Stern of Tel Aviv University said: “We found a disproportionately higher rate of the South African [B1351] variant among people vaccinated with a second [Pfizer/BioNTech vaccine] dose, compared to the unvaccinated group. Based on patterns in the general population, we would have expected just one case of the South African variant – but we saw eight.” She added that based on their findings, the B1351 strain can bypass through vaccine-induced immunity “to some extent.”

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