NO CITY IN America has been hit by covid-19 as hard as New York. By April 12th, according to official statistics, more than 6,000 people had died. This is over a quarter of all deaths in the whole country. There is some cause for hope: new reported covid-19 cases and deaths in the city both appear to be falling. Modelling by the Institute for Health Metrics and Evaluation, a research group at the University of Washington, suggests that New York state’s covid-19 epidemic may have passed its peak.

But when the final death toll is reported, it may be bigger than current data would suggest. A recent report from WNYC and The Gothamist, two New York media outlets, notes that the city’s official covid-19 fatality statistics have until recently excluded those who died in their homes, and therefore were never diagnosed with the virus. Exactly how many people are missing from the tally is unclear. One clue comes from the number of people calling 911 about cardiac arrests, a known consequence of covid-19.

According to data from the city’s fire department, New Yorkers are making four times as many emergency calls about cardiac arrests as they did last year. The most recent figures show that about 200 of these heart-attack victims are being pronounced dead at the scene each day, up from around 30 this time last year (see chart). It is plausible that some of these people were not victims of covid-19. Had hospitals not been so overwhelmed, they might otherwise have sought care early enough in person at emergency rooms, when they had their first symptoms, before things got bad enough to call an ambulance. Even so, the figures suggest that New York City (and possibly other places) may be drastically underestimating the number of people killed by the novel coronavirus.

The city has since announced that it will revise its covid-19 death count to include people who are likely to have died from the disease but who were never formally tested. Mortality statistics from governments tend to be reported with a significant time-lag. Officials might not know the full public-health impact of covid-19 until months after it has faded.