COVID-19 reinfections have been one of the largest unknowns during the pandemic. Can you get sick again? If so, when? How serious would a second or third infection be? Does being vaccinated reduce the likelihood of being reinfected? New data compiled by Oregon Health Authority (OHA) help answer these questions.  

Let’s start with some basic reinfection data.

As of Sept.1, OHA has documented:

• 35,466 second infections
• 660 third infections
• 11 fourth infections

It’s important to note that the number of reinfections listed above is likely a large undercount of the true number of reinfections in Oregon. We are only able to identify reinfection if a person’s initial infection and subsequent reinfection(s) were reported to public health. A more detailed explanation of the limitations may be viewed at the bottom of this blog.

The virus that causes COVID-19 mutates rapidly and has become more contagious with each new variant. New variants can, to some degree, resist prior immunity from both vaccination and infection. Additionally, as more and more people in Oregon have been infected, the pool of people who could get a reinfection is larger.

For the above reasons reinfections are becoming more common in Oregon.

Data show that reinfections occurred when Delta (2,148 reinfections) was the predominant variant but did not spike until the first wave of Omicron (17,803 reinfections) that started in Dec 2021 and lasted until March 2022. Another 15,183 reinfections were reported to public health from March 22 through Sept. 1, when Omicron subvariants were also predominant.

“When someone is infected with the virus (or vaccinated) they build antibodies to prevent infections,” said Paul Cieslak, medical director for Communicable Diseases and Immunizations at OHA. “These antibodies wane over time, so that as time goes on, the risk of reinfection slowly rises.”

“The Omicron subvariant had a lot of mutations in the spike protein,” Dr. Cieslak said. “That’s the part of the virus to which we’re making antibodies that keep the virus out of our cells. When there are mutations in the spike protein, our antibodies don’t stick to the virus quite as well.”

In our data, a case is considered a reinfection if a person with a previously confirmed or presumptive case meets the confirmed or presumptive case definition 90 days or more after the onset date of their first case. Someone who takes Paxlovid, for example, and experiences a rebound case a couple weeks later is not considered a reinfection. This is assumed to be the same infection that was suppressed by the treatment but returned.

Case severity

COVID-19 reinfections may be less severe than initial infections. Among cases overall, 4% have resulted in hospitalization and 1% have resulted in death. Among reinfections only, 2.8% of cases have resulted in hospitalization, and 0.4% have resulted in death.

As the chart below shows, while the number of reinfections has increased over time, the percentage of reinfection cases that have resulted in hospitalization or death has trended downward, starting with Wave 5 (when most people in Oregon got vaccinated). Additionally, the Omicron variant may cause less severe disease than previous variants.

Vaccinations reduce reinfections and severe disease

It will take more time to fully understand the degree to which vaccinations reduce long-term health complications from COVID-19. But currently the evidence is clear that people who receive their primary vaccine series plus booster doses when eligible are less likely to be reinfected, hospitalized or die from COVID-19.

The data are clear that vaccination prevents hospitalization and death. Since the start of the pandemic, nearly 1.07 million people in the U.S. and 8,726 people in Oregon have died from COVID-19. In the United States, through April 2022, it’s estimated more than 300,000 COVID-19 deaths could have been prevented if all adults were vaccinated. The data show that this pattern holds true in Oregon as well, and that vaccines prevent reinfection-associated deaths, too.

Forty-five percent of reinfections among adults age 18 and older in Oregon occurred among people who were unvaccinated, while just 15% occurred among people who were vaccinated as recommended. Forty-six percent of reinfection-associated hospitalizations and 40% of reinfection-associated deaths among adults occurred among people who were unvaccinated. Only 16% of reinfection-associated hospitalizations and 20% of reinfection-associated deaths occurred among people who were vaccinated as recommended.

With bivalent boosters now available, vaccination will be key in preventing both first-time and subsequent infections from COVID-19.

Immunity from COVID-19 infection wanes over time. The longer it’s been since your last infection, the more likely you are to get reinfected. You may consider waiting 90 days after infection to receive a COVID-19 vaccination (including an updated booster dose) to increase antibodies and maximize protection.

“Bivalent boosters should induce protection against a broader array of SARS-CoV-2 variants, reducing one’s chances of getting a reinfection or even a first infection,” Dr. Cieslak said. “And if one is infected, then vaccination offers the best protection against severe disease including hospitalization and death.”

* These counts exclude the following groups: presumptive cases; children ages 0-17; reinfections occurring before February 2021, when vaccines became widely available; adults who were partially vaccinated (i.e., received one dose in a two-dose series) or did not receive a booster(s) or complete a primary vaccine series when recommended. “Vaccinated as recommended” counts include adults who received a booster(s) when recommended or completed a primary vaccine series when recommended. Unvaccinated counts include adults who received 0 doses.