Breakthrough cases of COVID-19 are on the rise. That’s when a person becomes infected despite having been vaccinated. The reason for the current rise is twofold.

First, as the number of vaccinated people increases, so does the pool of people who can get a breakthrough infection.

Secondly, at this point (several months after thousands of people were vaccinated) some breakthrough cases are caused by our waning immunity to COVID-19. Scientists have shown that the number of virus-fighting antibodies circulating in your bloodstream decreases significantly over time. That doesn’t mean, however, that your body is completely unprepared to fight off SARS-CoV-2, the virus that causes COVID-19.

Our immune systems have ‘memories,’ and even after virus-fighting antibodies disappear, if we have been vaccinated our body can “remember” and rapidly produce them when needed. If SARS-CoV-2 infects you, and your once-plentiful supply of antibodies has dwindled, your immune system would simply create new antibodies–though it does take a few days. In addition to antibodies, vaccination prompts your body to develop an immune response in other ways. These different types of immune responses tend to stop breakthrough COVID-19 infections from becoming severe.

Waning immunity is why booster shots are so important. Boosters tell your body to create a new batch of fresh antibodies ready to fend off infection immediately, and they can also boost other immune responses to increase your defenses against severe disease. With the Omicron variant spreading rapidly, our bodies will need to be in fighting form. And best of all, unlike the initial vaccine doses, booster doses take effect quickly, within two to three days. You are considered up-to-date on your vaccines immediately after getting a booster.

Breakthrough cases and Omicron

Antibodies work by binding to the infamous “spike protein,” labeling the virus so our body knows to destroy it. The Omicron variant contains so many mutations that its spike protein has a slightly different shape than the original variant, making it harder for antibodies to bind to the virus.

This is why booster shots can make all the difference.

“If your body makes a lot of antibodies in response to a booster, enough of them might stick to the virus, offering us more protection,” says Paul Cieslak, one of OHA’s senior health advisors and an infectious disease expert.

Without a booster, “you’re only protected about 35% from Omicron,” Cieslak says. “A booster dose will induce more antibody creation, giving you up to 75% protection.”

For more information on when boosters are recommended for different vaccines and age groups, go to the CDC website. Please note certain changes effective today regarding the Pfizer vaccine and boosters.

Check out our weekly Breakthrough Report, published every Thursday in this newsletter.

Where to find a COVID-19 vaccine or booster

Call your health care provider about getting vaccinated or boosted. Or you can check out our regularly-updated list of Oregon’s high-volume vaccination sites. Boosters are free of charge. No insurance is required at any site listed.