COVID-19 vaccine 90% effective in real-world study in Duluth, seven other sites

A federal study with support from Duluth researchers has tracked the first two COVID-19 vaccines approved in the U.S. and found that they were 90% effective in real-world conditions and prevented asymptomatic infections.

Clinical trials of the Moderna and Pfizer vaccines looked only at prevention of symptomatic infections, so the latest study of their effectiveness in health care and emergency medical workers is a significant advance, said Dr. Harmony Tyner, an infectious disease specialist at St. Luke's Regional Health Care System in Duluth.

"It protects against asymptomatic infections as well," said Tyner, a co-author of the study published Monday by the U.S. Centers for Disease Control and Prevention. "We know it kept people alive, we know it kept people from dying, but [the clinical trials] didn't test against asymptomatic infections, which is huge."

The finding is a boost for aggressive vaccination as a key response to the pandemic in Minnesota, where there have been 6,835 COVID-19 deaths and 516,608 diagnosed infections with the novel coronavirus that causes the disease. The totals include five deaths and 1,550 infections reported on Monday amid continued signs of a new COVID-19 wave in Minnesota.

The state on Monday reported that 1,609,277 people have received a first dose of COVID-19 vaccine and 990,854 have completed the series either by receiving two Moderna and Pfizer shots or a single-dose of Johnson & Johnson vaccine.

All Minnesotans 16 and older will technically be eligible Tuesday to receive vaccine, but quantities remain limited and many medical providers are continuing to reserve doses for those at greatest risk of viral exposure or severe COVID-19 illness.

Gov. Tim Walz and former Gov. Tim Pawlenty are publicly receiving J&J vaccine shots on Tuesday.

The state reported that 81% of senior citizens and at least 66% of K-12 and child-care educators have received vaccine. They were initial priority groups in Minnesota along with long-term care residents, health care workers and non-elderly adults with qualifying medical conditions or front-line occupations.

Duluth is among eight locations that took part in one of the first real-world COVID-19 vaccine effectiveness studies in the U.S. The Minnesota site provided 448 volunteers, mostly clinic and hospital workers but some first responders as well, who submitted to COVID-19 testing every week before and after they were vaccinated.

Only 12 infections were detected between Dec. 14 and March 13 in the local study group, which included 47 people who were unvaccinated. That 2.7% infection rate was one of the lowest in the study and could have been due to the high vaccination rate in the group or due to higher viral transmission during the study period in other locations such as Arizona, Florida and Texas, Tyner said.

Among the 3,950 participants from all eight U.S. sites, 205 SARS-CoV-2 infections were identified — a rate of 5.2%. One-fourth of the study group remained unvaccinated during the study period.

The results showed 90% effectiveness for people who had been fully vaccinated — which means it had been 14 days after their final doses — and 80% effectiveness for partially vaccinated individuals, according to the CDC report. Clinical trials of the Moderna and Pfizer vaccine had shown about 95% effectiveness for fully vaccinated individuals.

"These findings should offer hope to the millions of Americans receiving COVID-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead. The authorized vaccines are the key tool that will help bring an end to this devastating pandemic," Dr. Rochelle Walensky, CDC director, said in a statement.

The study also found a much lower rate, at 10% of infections, with the SARS-CoV-2 virus that were asymptomatic. Estimates of such cases had been at 40% or higher, but Tyner said most people in the study who tested positive in the absence of symptoms ended up developing them later on.

Positive vaccine news could bolster new Minnesota advocacy campaigns, which were delayed until the state expanded access. Roughly 3.5 million Minnesotans already are eligible, but the latest expansion added 900,000 mostly young, healthy adults. The Minnesota Twins on Monday posted a "roll up your sleeves" social media message featuring Nelson Cruz and other star players.

Minnesota is gradually rolling back mobility restrictions designed to limit COVID-19 transmission — with the latest changes coming Thursday with allowances for large indoor and outdoor events at limited capacities. That includes Twins games for up to 10,000 fans, which is roughly 25% of the capacity of Target Field.

Proof that vaccines reduce asymptomatic infections could affect other public health responses, including mask-wearing practices for vaccinated people.

The CDC recently permitted unmasked visits without social distancing between fully vaccinated people, who also could visit with unvaccinated people at low risk of developing severe COVID-19.

However, the CDC has recommended mask-wearing in public for fully vaccinated people out of caution — because there was no evidence about their risks of spreading the virus through asymptomatic infection — and Minnesota's mask mandate applied to them as well.

The CDC study, titled HEROES-RECOVER, is ongoing and will continue to assess vaccine effectiveness over time. Tyner said the Duluth arm is looking for more volunteers in health care and first-responder roles who haven't been vaccinated yet and are willing to be tested regularly. Send a note to recoverstudy@slhduluth.com to sign up.

Health officials remain concerned about a new wave of COVID-19 fueled in part by spring break travels as well as the spread of more infectious variants of the novel coronavirus. Genomic sequencing has shown an increasing rate of infections in Minnesota due to a B.1.1.7 variant that has been problematic in Europe.

Daily pandemic totals in Minnesota have always been lower on Mondays due to reduced testing and reporting activities on weekends. Monday's total was the highest for a Monday since Jan. 4.

The key question for state health officials is whether the increase in diagnosed infections will be followed by more hospitalizations and then deaths — a pattern in the spring and fall that might not be repeated due to vaccination progress.

COVID-19 hospitalizations in Minnesota had increased from 210 on March 6 to 366 on March 26. The total dropped to 343 on Sunday.

Jeremy Olson • 612-673-7744