COVID-19 vaccine’s effectiveness declines, but remains a powerful disease deterrent

26 August 2021 13:30

COVID-19 vaccines remain effective, but their potency has declined in recent months, according to a national study at eight sites, including Salt Lake City, Utah.

Scientists calculated that the vaccine’s effectiveness was 80% in a large group of fully vaccinated frontline workers between December 2020 and August 2021, up from 91% in previous surveys. The estimates were based on COVID-19 RT-PCR testing and did not measure whether there were any changes in the effectiveness of protection against serious illnesses, including hospitalization and death.

The authors say one of the reasons for the change could be decreased immunity, a decrease in the strength of the body’s defenses activated by the vaccine against the virus. The difference may also reflect the fact that vaccines are not as effective against the highly contagious Delta variant of the SARS-CoV-2 virus, which since June 2021 has become the most common cause of COVID-19 in the United States.

“Vaccines are still helping to save lives and prevent people from getting sick despite a slight decline over several months,” explains Matthew Thiese, Ph.D., Associate Professor at the Rocky Mountain Center for Occupational and Environmental Health (RMCOEH) at the University of Utah. “This data, combined with other data, shows that people who have been vaccinated are much less likely to contract COVID-19 and are much less likely to be hospitalized. »Thiese is co-researcher and assistant professor RMCOEH Sarang Yoon, DO., is the principal investigator of the HERO-RECOVER (Research into the epidemiology of SARS-CoV-2 in essential response personnel) in Utah.

The study published on August 24 in the Morbidity Mortality Weekly Report (MMWR) Centers for Disease Control and Prevention (CDC). Additional study sites in the HEROES-RECOVER network are Phoenix, Tucson, and other areas of Arizona; Miami, Florida; Portland, Oregon; Duluth, Minnesota; and Temple, Texas.

The network followed 4,136 healthcare workers, first responders and essential workers who had never had COVID-19 before. Study participants submitted samples for RT-PCR testing every week and 2,976 participants were fully immunized during the study period, receiving either Pfizer-BioNtech (65%), Moderna (33 %) or Johnson & Johnson (2%). . The test results of these groups between December 14, 2020 and August 14, 2021 show that:

• Among the unvaccinated study participants, 194 infections occurred in 181,357 person-days (the combined total of the number of test days for this group).
• Among fully vaccinated participants, 34 infections occurred within 454,832 person-days.

During this period, the vaccines were 80% effective for all fully immunized study participants, but preliminary data indicates that vaccines may decrease in intensity over time with less effectiveness after five or more months. full vaccination. Additionally, vaccines appeared to be less effective in the last 43 days of the study period when Delta became the predominant viral variant. However, since the sample sizes were small, these results were not statistically significant. These trends will be explored in more detail in future studies.

“These data show that the vaccine is still quite effective against different strains of COVID-19, including the Delta variant,” says Thiese. “The protection people get from the vaccine prevents people from contracting COVID-19 at a 14 to 1 ratio. As this data continues to come in, it will help establish recommendations for masking, social distancing and booster injections. “

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