Infectious Virus Shedding May Be Lower in Breakthrough Cases

By Reuters Staff

August 24, 2021

(Reuters) - High viral loads in breakthrough infections after COVID-19 vaccination may not equate to high infectiousness, a new study suggests.

Among 24,706 vaccinated healthcare workers in The Netherlands, 161 developed breakthrough infections, mostly due to the Delta variant of the coronavirus. The infections were all mild or asymptomatic, occurring after receipt of vaccines from Moderna, Pfizer/BioNTech, Johnson & Johnson, or AstraZeneca.

Viral levels on nasopharyngeal swab samples were just as high in these patients as in unvaccinated healthcare workers who were infected last year with the original strain of the virus. But in test tube experiments, compared to the virus particles in the unvaccinated patients, the virus from the vaccinated patients was less efficient at reproducing itself, probably because it had been neutralized by antibodies from the vaccine, the researchers speculate.

In a report posted on medRxiv on Saturday ahead of peer review, they conclude that infectious virus shedding is reduced in breakthrough cases.

But "despite the reduced viral viability," they warn, breakthrough infections are still contagious.

SOURCE: medRxiv, online August 21, 2021.

SOURCE: medRxiv, online