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How big is the issue of breakthrough COVID cases?

How big is the issue of breakthrough COVID cases?

David Colburn
Posted 10/13/21

REGIONAL- Ever since the word “breakthrough” was added to the COVID-19 lexicon last spring to describe coronavirus cases in fully vaccinated individuals, state and federal officials have …

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How big is the issue of breakthrough COVID cases?

How big is the issue of breakthrough COVID cases?

Posted

REGIONAL- Ever since the word “breakthrough” was added to the COVID-19 lexicon last spring to describe coronavirus cases in fully vaccinated individuals, state and federal officials have been scrambling to determine the extent of the issue.
A person is considered fully vaccinated 14 days after they have received the final shot of their vaccination series.
The incidence of breakthrough cases drew the attention of the medical community and the national press when researchers discovered that the efficacy of the Pfizer vaccine diminished more rapidly than the Moderna and Johnson & Johnson vaccines. That prompted the CDC to recommend booster shots for certain groups of people six months after they had their second dose of Pfizer vaccine. Studies of the other two vaccines and the possible need for boosters is ongoing.
In early August, officials at the Minnesota Department of Health noted that between 25 and 30 percent of newly-diagnosed COVID cases were occurring in fully vaccinated individuals. At about the same time, MDH started issuing weekly updates specifically related to breakthrough COVID cases.
The report issued Monday showed that the cumulative number of breakthrough cases in the state since the start of vaccinations was 38,808, an increase of 6,012 from the prior week’s report. Cumulative hospitalizations from breakthrough COVID increased by 244, from 1,690 to 1,934. And the total number of deaths attributed to breakthrough cases also rose, from 185 to 234, an increase of 49.
But with more than 3.2 million Minnesotans fully vaccinated as of Sept. 12, what do the numbers actually mean, and how do they compare with the more familiar COVID measures of weekly cases and weekly case rates?
For help with those questions, the Timberjay contacted MDH Information Officer Doug Shultz.
“The proportion of people newly diagnosed with COVID who are vaccinated is currently still around 30 percent,” Shultz said last week. “However, that figure requires a large amount of context when reporting it and it comes from looking at multiple sources or streams of data, not just one set.”
Looking at the sleuthing process Shultz described for identifying breakthrough cases, hospitalizations, and deaths, it becomes clear that the weekly breakthrough reports aren’t the same as the weekly COVID case numbers reported by the state.
“The biggest problems with trying to show a week-by-week breakdown are the constant changes,” Shultz said. “Cases are reported late, vaccinations get reported later, we do a long run-match process, we spend time cleaning up errors, and new information gets reported. So, the data that gets posted on Monday is just a snapshot in time and does not necessarily reflect discreet or distinct weekly sums of new data that can be broken down by week. It’s out of date the minute it’s out the door. We aren’t doing real-time reporting and the cases week to week that are posted on the website are always going to change in retrospect as new counts come in. There are many, many ways you could cut or slice the data, and each one would give you a different picture and changes all the time.”
So, there’s no way of telling exactly when this week’s reported increases in cases, hospitalizations, and deaths actually happened. Some may have been within the past two weeks, while others may have occurred months ago but are just being reported now.
The analysis gets even more complicated when trying to compare the breakthrough data to other COVID measures, Shutlz said.
“If it’s all people who have COVID, the percent that you’re calculating can get really skewed,” Shultz said. “There will always be older people and people with serious underlying conditions that will be at risk for COVID even if they get vaccinated. Their immune systems just can’t handle it. And if you live in a nursing home or some other congregate care, you’re in a setting where disease can spread more easily. So, if you just look at cases to see how many are among vaccinated people it really misses the big picture of how many people in the whole state are vaccinated and are NOT getting COVID.”
The big picture
Overall, the data for Minnesota reported Monday shows that 98.8 percent of people who are fully vaccinated have not contracted COVID-19. That’s slightly higher than the “less than 99 percent” figure widely reported in August, but that’s to be expected, Shultz said.
“The percentage of cases that are breakthrough will continue to increase as more people are vaccinated - partly because no vaccine is 100-percent effective, partly because we will start to see waning immunity in those vaccinated earliest, and potentially because of things like the Delta variant, which is very transmissible and could be playing a role we don’t understand yet.”
And while about 30 percent of newly diagnosed cases in Minnesota currently involve fully vaccinated people, Shultz noted that the number illustrates that the unvaccinated are clearly at higher risk.
“It tells us that 70 percent of new COVID cases occur among the 30 percent of the population who are not vaccinated,” Shultz said. “More importantly, about 99 percent of people who are vaccinated do not get sick with COVID. That’s what the breakthrough data tell us.”
Research has also demonstrated that fully vaccinated people who contract COVID-19 are far less likely to experience severe illness, hospitalization, and death. The breakthrough data for Minnesota show that hospitalization among those fully vaccinated is quite rare.
And the risk of dying from COVID-19 among the fully vaccinated is far lower still. The 234 total deaths reported Monday represent only seven thousandths of one percent of those vaccinated.
Shultz said that MDH continues to refine the process of presenting the breakthrough data.
“It will likely fluctuate for a while depending on the future vaccine recommendations and testing behaviors of the public,” he said. “But we have been working on some ways to calculate some age-adjusted measures that we hope to put out in the near future that will better display the data and help to answer some of the questions we all have about all of this.”

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