PROVIDENCE – Fewer than 1 percent of Rhode Island blood donors had COVID-19 antibodies in April and May, a sign that residents adhered to state’s stay-at-home order and other restrictions, but a reminder that a lot are still susceptible to the contagious virus.
The seroprevalence rate in 2,008 blood donors from Rhode Island between April 28 and May 11 was .6 percent, according to a just-released study from researchers at the New York Blood Center. A separate study of about 500 residents released in June showed that 2.2 percent had antibodies.
Dr. Larry Luchsinger, who led the study, said the lower rate among blood donors could be that their median age was 56, significantly older than the median age all of Rhode Island residents, which is 39. Middle-aged and older people appear to honor rules about masks and distancing more than the younger crowd. Plus the race of the blood donors skewed white, and they lived in less-densely populated areas in the state.
“Considering the possibility that this may be an underestimate of the statewide population, these conclusions draw important findings as it suggests that in the absence of a vaccine, ‘background’ or ‘herd’ immunity to also be low, now four months into the US pandemic, and thus the susceptible population remains at 95 percent or greater,” the study states.
Luchsinger said the study suggests that the state’s decision to close most businesses in April and May helped slow the spread of the virus.
“Life is a series of tradeoffs,” Luchsinger said. “If we were to not do a lockdown, more people would have gotten it. We traded that scenario for one where no one gets it.”
Rhode Island, which has a population of just over one million residents, has seen more than 19,000 positive tests since March 1, and 1,007 people have died. The number of infections peaked in late April before falling dramatically in May and June as the state began to reopen. Cases ticked up again last month, prompting Raimondo to limit social gatherings to 15 people.
Luchsinger said the low seroprevalence rate in the blood donor study shows that residents complied with Raimondo’s orders – including a requirement to wear masks in public – and that the state was successful in not overwhelming the health care system.
“That was the goalpost in the beginning - not overrunning health care and limiting deaths,” he said.
Luchsinger stressed that it’s still unknown how long antibodies remain in a person’s body, and it’s unclear how common it is for people to be infected twice.
Dr. Phillip Chan, a consultant medical director to the Rhode Island Department of Health, said the state believes that the 2.2 percent seroprevalence rate in the state’s separate study is more reflective of the entire state, but he said “the results of both of these studies are good news.”
“The low percentages are reflective of multiple, statewide mitigation efforts that work,” Chan said.
The New York Blood Center study makes Rhode Island one of the first states where researchers are evaluating seroprevalence using blood donations.
Because infection rates were so low in donors, Luchsinger warned that more residents could get the virus in the coming months.
“In the absence of a vaccine, you’re still at risk,” Luchsinger said.