A promising new report from the US Centers for Disease Control and Prevention (CDC) has found less than 1,000 cases of COVID-19 needing hospitalization out of more than 100 million fully vaccinated people. The CDC admits it is probably undercounting positive COVID-19 cases, however, the report offers a powerful reminder of the real-world effectiveness of vaccines.
The CDC report chronicles a volume of what are called "breakthrough infections." These are positive COVID-19 cases seen in subjects who are at least 14 days post all recommended doses of a vaccine.
By April 30, 2021, the CDC reports around 101 million fully vaccinated individuals in the United States. Amongst that large fully vaccinated cohort, the CDC says only 10,262 breakthrough infections were officially recorded.
Around a quarter of those breakthrough infections were classified as asymptomatic. Just 995 of these infections led to hospitalization, and only 160 deaths were recorded. The average age of those patients who died was 82, and nearly 20 percent of the deaths were reported as potentially unrelated to COVID-19.
The CDC is cautious to note the limitations of the report, in particular noting that the overall breakthrough infection numbers are highly likely to be undercounted.
“…the number of reported COVID-19 vaccine breakthrough cases is likely a substantial undercount of all SARS-CoV-2 infections among fully vaccinated persons,” the report states. “The national surveillance system relies on passive and voluntary reporting, and data might not be complete or representative. Many persons with vaccine breakthrough infections, especially those who are asymptomatic or who experience mild illness, might not seek testing.”
Despite the potentially larger number of uncounted asymptomatic or mild COVID-19 cases, the stunningly small volume of hospitalizations and deaths in vaccinated individuals echoes another recent large real-world study out of Israel. That study, published in The Lancet in early May, looked at nearly 5 million people vaccinated with the Pfizer mRNA candidate. It found 95.3 percent of those vaccinated were protected from symptomatic infection.
Another recent real-world CDC study looked at mRNA COVID-19 vaccines in those aged over 65. It found vaccination reduced the risk of hospitalization from COVID-19 in that age group by 94 percent.
Influenced by these recent findings the CDC has now moved to primarily monitoring breakthrough infections in hospitalized patients. At a recent briefing CDC director Rochelle Walensky argued the agency’s key focus is on severe illness and death.
“You know these vaccines were studied to prevent severe illness, hospitalization and deaths. And as we look at these breakthrough infections these are the ones we're most concerned about,” says Walensky. “Before we started only studying breakthrough infections in only hospitalized patients, we were studying all breakthrough infections. What we were starting to find is a large portion of them were fully asymptomatic and in fact when we went to study them and sequence them there was inadequate virus to even do so.”
However, not everyone is confident this new CDC focus on just monitoring severe COVID-19 cases is the correct approach. While the CDC argues it is reasonable to concentrate on monitoring severe cases that lead to hospitalization, others are claiming this could mean new surging virus variants could be missed.
“If there is a new variant or there is a change in frequency of a variant, you might want to find out earlier than wait for it to appear in severe and hospitalized cases,” says Saad Omar, an infectious disease epidemiologist from Yale University. “That gives you the ability to be ahead of the outbreak rather than follow it.”
Source: CDC
