Who's Least Likely to Get a 'Breakthrough' Case of COVID?

TUESDAY, April 26, 2022 (HealthDay News) -- Are you vaccinated and wonder what your chances are of a breakthrough COVID-19 infection?

A new study answers that question: Breakthrough COVID infections in fully vaccinated people are least likely to occur in those who've received an mRNA vaccine and who were infected with the coronavirus before vaccination.

The study included more than 8 million adults in Belgium, aged 18 and older, who were fully vaccinated between Feb. 1 and Dec. 5, 2021. From 14 days after their second dose, they were followed for up to an average of 150 days.

The incidence rate of breakthrough infections was 11.2 per 100 person-years, meaning that if 100 participants were followed up for one year, 11.2 would be expected to have a breakthrough infection.

People who received a viral vector vaccine (Oxford/AstraZeneca or Johnson & Johnson/Janssen) had a higher risk of a breakthrough infection than those who received an mRNA vaccine (Pfizer or Moderna).

Compared to the Pfizer vaccine, the Oxford vaccine was associated with a 68% higher risk of a breakthrough infection, and the J&J vaccine was associated with a 54% higher risk, the findings showed.

The study also found that people who received the Moderna vaccine had a 32% lower risk of breakthrough infection than those who received the Pfizer vaccine.

In addition, those who were infected with the coronavirus before vaccination were 77% less likely to have a breakthrough infection than those who were never infected.

Rates of breakthrough infections were higher among those aged 18 to 64 than among those 65 and older, which may be due to differences in social behavior, the researchers suggested.

Health care workers were 40% less likely to develop a breakthrough infection than non-health care workers, possible because health care workers had high vaccination rates and extensive use of personal protective equipment (PPE) while at work.

Of nearly 217,000 breakthrough infections with information available on symptoms, 70% were symptomatic, and the most common symptoms were runny nose, cough and headache.

Those with an infection before vaccination were 62% less likely to have symptoms with a breakthrough infection than those with no previous infection, according to study author Veerle Stouten and colleagues at Sciensano, the National Public Health Institute of Belgium.

Their study was presented at the European Congress of Clinical Microbiology & Infectious Diseases in Lisbon, Portugal, held April 23 to 26, and published in the journal Viruses.

"We identified risk factors associated with breakthrough infections, such as vaccination with adenoviral-vector vaccines, which could help inform future decisions on booster vaccination strategies internationally," Stouten said in a meeting news release.

"Moreover, we observed that hybrid immunity of combined prior infection and vaccination not only lowered the risk of breakthrough infections but also of having symptoms when experiencing a breakthrough infection, highlighting its protective effect," she added.

"The majority of the breakthrough infections included in the study occurred during the period when the Delta variant was dominant," Stouten noted. "We expect to see similar patterns regarding characteristics of breakthrough infections due to the Omicron variant, but we need to continue to monitor breakthrough infections and study their severity and multiple recurrences, as well as the role of emerging variants to confirm this."

More information

There's more on breakthrough infections at Johns Hopkins Medicine.

SOURCE: European Congress of Clinical Microbiology & Infectious Diseases, news release, April 25, 2022