EAU CLAIRE — A small number of fully vaccinated people in Eau Claire County have contracted COVID-19, in what some experts call “breakthrough infections.”

Experts say breakthrough infections are very rare, but not surprising, given the large numbers of people who have now been vaccinated in the U.S.

Four fully vaccinated Eau Claire County residents had contracted COVID-19 as of April 1, a Health Department spokesperson said.

The Health Department did not give a total Thursday of how many vaccinated county residents have experienced breakthrough infections, but “our number is very low” in Eau Claire County and across Wisconsin, said Health Department director Lieske Giese at a Thursday press conference.

Wisconsin health officials said this week that only 0.03% of fully vaccinated people have later tested positive for COVID-19. The Wisconsin State Journal reported Wednesday that just 605 people out of 1.8 million fully vaccinated Wisconsin residents had contracted the virus.

“This is not unexpected,” Giese said.

In Eau Claire County, the few breakthrough infections are “typically much less significant of an infection,” Giese said. The county hasn’t seen people with breakthrough infections that become hospitalized or die, but it is with people who aren’t vaccinated, she added.

Breakthrough cases of COVID-19 aren’t a signal that the vaccines don’t work, said Dr. Gregory Poland, director of the Mayo Clinic vaccine research group.

“There is no vaccine that has 100% (efficacy). There’s no such thing. This is true for every vaccine,” Poland said at a Thursday press conference.

The Moderna and Pfizer vaccines were found to have 95% efficacy. That doesn’t mean specifically that 95% of people who get those vaccines are protected, Poland said.

“Compared to a group with no vaccine protection, the protection in the vaccinated group is 95% more,” Poland said. “So there are going to be people, either because of their genetic background, maybe medications they’re taking (or) the diseases they have, who won’t respond well or with protective levels of immunity. They may get varying levels of infection and symptoms, even after being fully vaccinated.”

So far in the U.S., the number of vaccinated people who have tested positive for COVID-19 is very small.

About 0.008% of fully vaccinated people have tested positive for the virus, or roughly 7,000 out of 87 million people, though the Centers for Disease Control and Prevention cautioned that breakthrough infections are almost certainly undercounted in the U.S. since many are likely mild or asymptomatic infections.

Some researchers believe tracking breakthrough infections could help the fight against new COVID-19 variants — by looking for patterns in breakthrough infections, they may be able to more quickly identify dangerous variants that evade vaccine immunity, the MIT Technology Review reported Thursday.

People don’t have the vaccine’s full protection until 14 days after Johnson & Johnson shot, or 14 days after their second Moderna or Pfizer shot, Poland cautioned.

Local cases stay flat; vaccinations slowing

After its briefing next week on May 6, the Health Department will stop holding weekly COVID-19 briefings, Giese said.

“We will continue to do briefings as needed … we’ll update our website and social media regularly,” she noted.

The trajectory of new COVID-19 cases in Eau Claire County stayed flat this week; about 44 new cases were reported in the last week.

Two more county residents were hospitalized with the virus this week, and two more died of COVID-19 this week as well, according to county data.

Fewer people got newly vaccinated this week, but the rate of vaccines in the county is still climbing: 45% of Eau Claire County residents have gotten at least one dose, and about 37% are fully vaccinated.

The Health Department’s goal is 80% of the county vaccinated, a benchmark at which public health officials say the community may reach herd immunity.

Contact: 715-833-9206, sarah.seifert@ecpc.com, @sarahaseifert on Twitter

Sarah Seifert is the L-T's education and health reporter. She has worked as a journalist in the Chippewa Valley since 2017 and joined the L-T in 2019. Get in touch at sarah.seifert@ecpc.com or on Twitter @sarahaseifert.