Breakthrough COVID-19 More Likely Months After Vaccination

By Reuters Staff

August 11, 2021

(Reuters) - People who received their second dose of the Pfizer/BioNTech vaccine five or more months ago are more likely to test positive for COVID-19 than people who were fully vaccinated less than five months ago, new data suggest.

Researchers at an Israeli HMO studied nearly 34,000 fully vaccinated adults who were tested to see if they had a breakthrough case of COVID-19. Overall, 1.8% tested positive.

At all ages, the odds of testing positive were higher when the last vaccine dose was received at least 146 days earlier, the research team reported on medRxiv ahead of peer review. Among patients older than 60, the odds of a positive test were almost three times higher when at least 146 days had passed since the second dose.

Most of the new infections were observed recently, said coauthor Dr. Eugene Merzon of Leumit Health Services in Israel.

"Very few patients had required hospitalization, and it is too early to assess the severity of these new infections in terms of hospital admission, need for mechanical ventilation or mortality," he added. "We are planning to continue our research."

SOURCE: medRxiv, online August 5, 2021.