To assess the likelihood of the spread of coronavirus vaccinated and unvaccinated, scientists at Imperial College London analyzed data from 621 people, whose relatives confirmed COVID-19 from September 2020 to September 2021.
Among vaccinated family members, the rate of infection with the delta variant of SARS-CoV-2 was 25%, while people who did not receive the vaccine had contact with infected loved ones, this figure was 38%.
Scientists noted that most of those vaccinated with breakthrough infections received the vaccine a long time ago, which indicates a gradual weakening of immunity and the need for revaccination.
Another important finding was that those infected with the delta variant of the vaccinated people had the same viral load as the infected unvaccinated. At the same time, vaccinated patients, on average, tolerated COVID-19 more easily and recovered faster, and the viral load in infected with the delta variant decreased faster than with the alpha variant.
“Vaccinated people can become infected themselves and transmit the infection within households, including vaccinated family members,” the study authors said.
Note that in earlier studies conducted before the widespread use of the delta variant, it was noted that vaccinated people have a much lower viral load when infected than unvaccinated ones, so the risk of transmission is less. So, in infected patients in Israel who received the vaccine, the number of viral particles in test nasal swabs was 60% less than in unvaccinated ones. In a study in the United States, the viral load in this group was, on average, 40% lower than in the unvaccinated.
“Immunity weakens over time, it is imperfect, so transmission of the virus still occurs, and therefore the revaccination program is so important,” the authors of the new study say.