You asked, we answered: Is it true that 80% of new COVID-19 cases are occurring in vaccinated people?

Published December 23, 2021

Published

James Lawler, MD
Infectious diseases expert James Lawler, MD, MPH

Question:

Why should someone get the vaccine when 80% of new COVID cases are in the ones already vaccinated?

Answer from infectious diseases expert James Lawler, MD, MPH:

Because this statistic is from a very small sample size and is not the full picture. Written this way, this statistic is not accurate and is missing critical context. 

The information this statistic is based on came from some very early omicron-specific data recently published by the U.S. Centers for Disease Control and Prevention

Here is that data with all the context:

  • Of the 43 cases attributed to the omicron variant, 34 people had been fully vaccinated
  • 14 of the fully vaccinated people had also received a booster, however, five of those 14 omicron cases occurred less than 14 days after the additional shot before full protection kicks in

When looking at early statistics like these, it's important to remember that ascertainment and observation bias matter. 

Currently, 72% of U.S. adults are fully vaccinated. The vast majority of omicron cases detected so far in the U.S. have been related to adults participating in international and domestic travel. We can expect that the vaccination rate among this pool of people is much higher than the general U.S. population. Essentially 100% of international travelers coming into the U.S. are fully vaccinated. 

In addition, people who are vaccinated are more likely to get tested for COVID-19 than those who aren't. Because unvaccinated people are less likely to seek out testing, they're also less likely to be counted as early cases. 

So what is the full picture? What can we expect with omicron?

The facts are:

  • Locally, our hospital systems are stretched to capacity. This may affect our ability to care for patients with other health care problems
  • Based on a study recently published by Discovery Health, a South African health insurer, the two-dose Pfizer vaccine appears to be about 30% effective at preventing an omicron infection overall, but 70% effective at preventing hospitalizations. Please get vaccinated and boosted
  • Based on data from the United Kingdom and South Africa, omicron appears to be more transmissible than delta. And preliminary data from a South African study indicate omicron may cause slightly less severe disease, with a 30% reduction in hospitalizations

Some are celebrating this last point – that omicron is more contagious but less severe. I explain why we should not be celebrating this with a mathematical exercise in my Dec. 15 update. You can watch the exercise below, beginning at about the 12-minute mark.