D-H Infectious Disease Physician Provides Guidance on the COVID-19 Delta Variant

Michael Calderwood, MD, MPH, chief quality officer at DHMC

The higher transmission and lower effectiveness of some of the vaccines means we now need to vaccinate more than 90 percent of the population to reach herd immunity.

Michael Calderwood, MD, MPH, chief quality officer at Dartmouth-Hitchcock Medical Center

The Delta variant (B.1617.2), which originated in India, is now the dominant variant of COVID-19 in the United States, and is more transmissible than the original virus. It is also connected with four times the risk of hospitalization for unvaccinated individuals compared to the original virus.

 "Those who are fully vaccinated are well protected against this variant despite a small decrease in the overall level of protection provided by vaccines which supports the continued need to vaccinate more people," said Michael Calderwood, MD, MPH, chief quality officer at Dartmouth-Hitchcock Medical Center. "Both the Moderna and Pfizer vaccines remain 80-90 percent effective in preventing symptomatic COVID-19 from the Delta variant and more than 90 percent in preventing severe disease leading to hospitalization."

Vaccine hesitance still remains a factor in the ability to achieve a measurable level of herd immunity (which is the proportion of a population that is protected from infection either from having the disease or being vaccinated). A recent Household Pulse Survey, by the U.S. Department of Health and Human Services, found that, in New Hampshire, 11.3-13.6 percent of individuals were hesitant or unsure about getting the vaccine, and 6.1-7.0 percent were strongly hesitant. The top three reasons noted: “don’t trust COVID vaccines,” “don’t trust the government” and “don’t believe I need it.” "It is that last reason where we have the most opportunity to increase vaccination, especially among those who are younger than 30 years of age. Some of these individuals will be vaccinated as a requirement for school or work, but most will need to be convinced that they remain at risk if unvaccinated," said Calderwood.

With the Delta variant, the ability to reach herd immunity has also changed. "We’ve had lower rates of infection in our area, which means we have less natural protection," continued Calderwood. "The higher transmission and lower effectiveness of some of the vaccines means we now need to vaccinate more than 90 percent of the population to reach herd immunity." Currently, the percentage of the total population fully vaccinated in New Hampshire is 58 percent (66 percent of those 12 and older who are currently eligible for the vaccine), and Vermont is 67 percent (76 percent of those 12 and older who are currently eligible for the vaccine).

Though COVID-19 will continue to evolve, getting vaccinated is the best way that everyone can help to combat transmission and keep their families, colleagues and communities safe. To find out where you, your family members or others in your community can get vaccinated, call the D-H COVID Hotline at (603) 650-1818, visit www.dartmouth-hitchcock.org/covid19/vaccine-updates or Vaccine.govs.

About Dartmouth-Hitchcock Health

Dartmouth-Hitchcock Health (D-HH), New Hampshire’s only academic health system and the state’s largest private employer, serves a population of 1.9 million across northern New England. D-HH provides access to more than 2,000 providers in almost every area of medicine, delivering care at its flagship hospital, Dartmouth-Hitchcock Medical Center (DHMC) in Lebanon, NH. DHMC was named again in 2020 as the #1 hospital in New Hampshire by U.S. News & World Report, and recognized for high performance in 9 clinical specialties and procedures. Dartmouth-Hitchcock Health includes the Norris Cotton Cancer Center, one of only 51 NCI-designated Comprehensive Cancer Centers in the nation Children's Hospital at Dartmouth-Hitchcock, the state’s only children’s hospital; member hospitals in Lebanon, Keene, and New London, NH, and Windsor, VT, and Visiting Nurse and Hospice for Vermont and New Hampshire; and 24 Dartmouth-Hitchcock clinics that provide ambulatory services across New Hampshire and Vermont. The D-HH system trains nearly 400 residents and fellows annually, and performs world-class research, in partnership with the Geisel School of Medicine at Dartmouth and the White River Junction VA Medical Center in White River Junction, VT.