'Breakthrough' COVID: How Effective Are the Vaccines?

By Chuck Dinerstein, MD, MBA — May 26, 2021
Phase III trials put the efficacy of the two earliest COVID-19 vaccines in the mid-’90s, certainly more than we had hoped. The word on the media “street” has been that vaccinations result in fewer hospitalizations and no deaths. The CDC is now reporting on “breakthrough infections” since the beginning of the year. 
Image by Jeyaratnam Caniceus from Pixabay

The "boots on the ground" when it comes to surveillance are the state health departments that, in turn, rely on the reporting of local health departments. The CDC aggregates the information and investigates the cases. Let’s start with a definition. A breakthrough infection occurs when COVID-19 is detected based upon RNA or antigens in the “respiratory specimen” (a more polite way to describe phlegm) in a person who has completed their immunization at least 14 days previously.

What they found

As of April 30th,

  • 101 million individuals have been fully vaccinated in the US
  • As evidenced by the CDC graphic, case volume and deaths are dramatically dropping in the general population. For example, during the last week of the reporting period, there were 355,000 new cases of COVID-19; this week there were roughly half, 166,000.
  • There have been 10,262 breakthrough cases reported. That is 0.01% of the vaccinated. These vaccines, and this includes J&J, work exceedingly well.

The Demographics of those "breaking through"

  • 6,446 (63%) in women, consistent with the demographics of the vaccinated.
  • Median age 58
  • 27% were asymptomatic
  • 10% “were known” to be hospitalized. Within that group, another “29% were asymptomatic or hospitalized for a reason unrelated to COVID-19.” That would bring the asymptomatic percentage up to almost 47%
  • 160 of these individuals died. For the breakthrough cohort, this was a case-fatality rate of 2%. It is difficult to determine the current case-fatality rate for our general population, but, I believe, an estimate of 1.78% is not far off. That, of course, suggests that breakthrough cases fare no worse than the unvaccinated. But when talking about the vaccines’ protection against death, the case fatality rate would be roughly 0.00015% - 4 fold less.
  • The median age of those dying was 82, and nearly 20% of these individuals were asymptomatic or died from “a cause unrelated to COVID-19.”
  • Only a tiny fraction, 5%, had specimens with sequencing data. Of those cases, two-thirds involved variants of concern – predominantly the British B.1.1.7 variation. The proportion of cases attributed to these variants, and again the number is exceedingly small, reflects the ratio of the variants in circulation.


The CDC believes they are reporting an undercount of breakthrough cases because reporting is voluntary and needs to be sent to the CDC; they are not actively requesting the information. More importantly, the asymptomatic may not be seeking medical attention and therefore not be identified. I will give the last word to the CDC.

“FDA-authorized COVID-19 vaccines are safe and effective. CDC recommends that all persons aged ≥12 years be vaccinated with an FDA-authorized COVID-19 vaccine.”


Source: COVID-19 Vaccine Breakthrough Infections Reported to CDC — United States, January 1–April 30, 2021 MMWR


Chuck Dinerstein, MD, MBA

Director of Medicine

Dr. Charles Dinerstein, M.D., MBA, FACS is Director of Medicine at the American Council on Science and Health. He has over 25 years of experience as a vascular surgeon.

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