By Molly Walker

Jumps in New York City's overall mortality during its COVID-19 peak were even higher than in the 1918 flu pandemic there, researchers found.

From March 11 to May 11, COVID-19 was associated with four times as many expected deaths versus corresponding periods from 2017-2019 (incident rate ratio for all-cause mortality 4.15, 95% CI 4.05-4.24, whereas the 1918 flu pandemic was associated with almost three times as many expected New York City deaths versus corresponding periods in 1914-1917 (IRR 2.80, 95% CI 2.74-2.86), reported Jeremy Faust, MD, of Brigham and Women's Hospital in Boston, and colleagues in a research letter.

While the absolute increase in per-capita all-cause mortality was higher in 1918 than this year, the modern baseline was "less than half" of that in 1914-1917, due to improvements in hygiene, medicine treatment, and safety.

For the last several months, Faust and Carlos del Rio, MD, of Emory University School of Medicine in Atlanta, examined flu data in New York City compared with the COVID-19 outbreak in the spring. First, in a preprint manuscript published in April, they found the ratio of excess deaths in New York City from February to April was 21 times the number of deaths from seasonal influenza. They then followed up with an "apples to apples" comparison of COVID-19 deaths for 1 week in April in the U.S. compared with mean number of flu deaths from influenza in the worst weeks of the 2013-2020 flu season, and found a similar 20.5-fold mean increase.

But if one is going to compare COVID-19 and flu, how does the current pandemic compare the deadliest influenza pandemic in history, with 50 million influenza-related deaths worldwide, including 675,000 in the U.S.? As of press time, the COVID-19 pandemic has killed over 165,000 people in the U.S., according to unofficial counts.

"Few persons in the U.S. have a frame of reference for the historic levels of excess mortality currently being observed during the coronavirus disease 2019 (COVID-19) pandemic," Faust, del Rio, and Zhenqiu Lin, PhD, of Yale New Haven Hospital, wrote.

They used CDC data from 1914-1918, as well as data from the New York Department of Health and Mental Hygiene from 2020 and data from the U.S. Census Bureau from 2017-2020.

Excess mortality in absolute terms was higher for the 1918 flu compared to COVID-19 in New York City (incident rate 287.17 deaths per 100,000 person months vs 202.08 deaths per 100,000 person months, respectively). Early months of the COVID-19 outbreak in New York City yielded more total all-cause deaths than the 1918 flu pandemic there (33,465 vs 31,589 deaths, respectively). The city's population in 1918 was about 5.5 million, versus 8.4 million currently.

Limitations to the data include inability to compare the "native virulence" of the 1918 influenza H1N1 strain and SARS-CoV-2. Also, in seeking to compare the current situation with 1918, the researchers pointed to the many medical innovations in the past century that presumably kept the COVID-19 death toll from being even greater.

"We believe that our findings may help officials and the public contextualize the unusual magnitude of the COVID-19 pandemic, leading to more prudent policies that may help to decrease transmission by decreasing the effective reproduction number of SARS-CoV-2," Faust and colleagues concluded.