UK dental professionals were at heightened occupational risk for COVID-19 infection early in the COVID-19 pandemic, according to an observational study yesterday in the Journal of Dental Research.
A team led by University of Birmingham researchers obtained blood samples from 1,507 dentists, dental nurses, and dental hygienists in the Birmingham, England, region in June 2020. They found that 16.3% of participants had SARS-CoV-2 antibodies, compared with an estimated 6% to 7% of the general population. Dental receptionists who don't have direct patient contact, however, were no more likely than community members to have coronavirus antibodies, at 6.3%.
Race was a significant risk factor for COVID-19, as shown by antibody detection in 35.0% of Black and 18.8% of Asian dental professionals, versus 14.3% of White participants. Living in socioeconomically disadvantaged areas was also a risk factor. The authors noted that although the study had a relatively small sample size, the results were similar to previous studies involving non-dental healthcare workers.
Antibodies lingered for 6 months in most
The researchers obtained follow-up blood samples from most participants in September 2020, after dentist offices had reopened with improved personal protective equipment (PPE) and infection-control protocols, and again in January 2021, amid the second pandemic wave and healthcare worker vaccination rollout.
Of professionals who had SARS-CoV-2 antibodies at the first blood draw, over 70% still had antibodies 3 and 6 months later, and their risk of reinfection was 75% lower than those not previously infected.
From June 2020 to January 2021, seroprevalence rose 12.3% in the Birmingham area while infection risk in seronegative study participants was 11.7%. "This implies that the enhanced PPE and infection control practices appeared effective in reducing risk of occupational exposure of [dental professionals] to SARS-CoV-2 to background population levels," the researchers wrote.
By January 2021, antibodies were detected in 51.4% of all participants and in 19.7% of professionals who were seronegative at baseline, which the researchers attributed to natural infection.
No participants who had blood antibody levels above 147.6 International Units per milliliter (IU/ml) tested positive for COVID-19 from the first to the last blood draws. Noting that only 5.3% of participants had an antibody level above 147.6 IU/ml during the first pandemic wave, corresponding study author Thomas Dietrich, MD, DMD, said in a University of Birmingham press release, "This suggests that natural infection alone is unlikely to generate meaningful, durable herd immunity."
The only reinfected professionals were those without a detectable anti-spike protein immunoglobulin G (IgG) response, either because they had undetectable IgG concentrations at baseline or because their IgG response dwindled over time.
Among participants with antibodies, 60.2% recalled having a symptomatic illness, 25.6% reported cough, 23.3% reported fever, and 39.0% said they lost their sense of taste or smell.
The study also showed that the first dose of the Pfizer/BioNTech COVID-19 vaccine generated a 97.7% antibody response after 12 days in participants not previously infected. Those who had antibodies at the first blood draw had an even faster and more robust immune response after the first dose.
A start to defining protective antibody levels
Lead author Adrian Shields, MBBS, PhD, said in the release that understanding the meaning of antibody tests results is critical to ending the pandemic.
"Our study has taken the first steps in defining the level of antibody in a persons' blood necessary to protect them from infection for six months," he said. "Furthermore, by comparing the antibody levels we have found in dentists to those contained in widely available reference material produced by the World Health Organization, we hope the protective level we found can be easily confirmed and compared by other laboratories."
Dental professionals have been thought to be at increased occupational risk of COVID-19 because of their routine exposure to patients' airways and performance of aerosol-generating procedures, the authors said.
The researchers called for future research on the efficacy of COVID-19 vaccination strategies (eg, different doses, vaccine combinations) and on variants of concern. "Further studies are necessary to comprehensively understand whether these comparative statistics represent a true lowering of exposure rates of [dental professionals] following reopening of general dental practices and the additional precautions taken to ensure practices became COVID-19 secure," they wrote.