It has to be one of the most macabre things about this already ghastly year.
In the United States there is a digital tool which allows users to assess their risk of Covid-19 infection based on where they are and the size of the event they are thinking of attending.
A map of the US shows counties colour-coded according to risk level, from the mild yellow of under 1 per cent to the brick red of more than 99 per cent.
No guesses as to which is the dominating colour when the calculation is based on holding events with 50 people.
Social media users have been using it to calculate their odds of rubbing shoulders with someone carrying Covid in gatherings of, say, 10 people. Journalists worked out it's about a 39 per cent chance in Cook county, Illinois, and a 93 per cent risk in Dewey county, South Dakota.
The US is in hellish limbo as President Donald Trump fiddles while the coronavirus burns through the country. On Saturday, at least 172,009 people tested positive, the highest number of daily cases since the pandemic began. The University of Washington forecast model projects nearly 440,000 dead by March.
New Mexico and Oregon have become the first US states in the current surge to introduce circuit-breaker near lockdowns for two weeks. A new mask mandate is in place in North Dakota. The governors of California, Oregon and Washington have urged people entering or returning to their states to self-quarantine.
The question of lockdowns is a thorny one for President-elect Joe Biden, who has pushed for the more achievable goal in the US of greater mask-wearing.
US health officials are trying to encourage Americans to wear masks by emphasising recent research that a mask protects the person who wears it.
Previously, the Centres for Disease Control and Prevention advised people to wear masks because of evidence it stops people who are infected from spreading it.
CDC officials highlighted a study by Japanese researchers who used mannequins and artificial respirators to simulate the spread of coronavirus particles, and analyse how well masks blocked transmission.
It confirmed earlier research that masks work best when worn by an infected person. Masks block about 60 per cent of the virus from an infected person.
When an uninfected person wearing a mask was near an infected person who wasn't wearing one, the amount of virus the uninfected person inhaled fell by 37 per cent. When both were wearing masks, the reduction was about 70 per cent.
New Zealand's slowness on mask-wearing has been a disappointing feature of the country's Covid-19 response. It's so obviously a good idea to get the public used to regularly wearing them on public transport and in crowds, not just for this pandemic but for future ones. A culture of using masks and good testing and tracing is preferable to movement restrictions if possible.
A move for masks to be mandatory for everyone travelling on domestic flights and for Aucklanders using public transport from as early as Thursday is welcome.
The public health order - similar to one issued in August requiring mask use under alert level 2 - is expected to be presented to Cabinet today.
Infectious diseases expert Professor Michael Baker wants a wider review of the alert levels and would like to see a level 1.5 with mass mask-wearing.
The Government is once again being reactive - this time to the latest community case - rather than proactive.
Just because we don't have the wildfire virus spread in areas of the US and Europe, doesn't mean we can't improve our approach.