Thread by @DocJeffD

Why are COVID-19 cases falling and what does it tell us about where the pandemic is heading? A few thoughts:
1/

Factors contributing to recent surge(s) are decreasing. These include holiday travel/get togethers, more activities & socializing, & general increase in indoor time during fall & winter that facilitate CoV-19 transmission through airborne spread & effects of low humidity. 2/

Restrictions on indoor and other activities (Governor’s directives in WA state: travel advisory, mask use, distancing) work and helped decreased spread. 3/

Decrease in human “dry tinder” feeding the CoV-19 wildfire. "Re" (the # of people infected by each person w/CoV-19) has been falling. 4/

I think this is at least in part due to the fact that increasing # of people in larger/more active social networks have been infected & developed some immunity (at least short term), making it harder/slower for virus to find susceptible in the network to spread to (for now). 5/

Most people, especially people who have been hunkering down & minimizing contact with others, remain susceptible but with more activity & opportunities for transmission, Re will likely increase. 6/

I don’t think “seasonality” explains the current drop given that the season has not changed recently & similar drops are seen in areas with different environmental conditions. 7/

I do think “seasonality” will have a beneficial impact when weather & relative indoor humidity increase, & more activities shift to outdoor & better ventilated indoor environments. 8/

Increasing vaccine coverage will be the key factor going forward, but hard to attribute the dramatic drop in cases beginning in early JAN '21 across age groups to vaccine given the relatively few that are vaccinated currently. 9/

As more people are vaccinated, this will be the most important driver of decreasing CoV-19 cases, hospitalizations & deaths. 10/

Disclaimer: I'm mindful that there is a lot we don’t understand about this new emerging virus & how it spreads. Both predicting & explaining are fraught with uncertainty. A dose of humility is in order at all times when prognosticating & especially, pontificating. 11/

That said, what does all this mean for what we can expect over the next few months? There are good reasons for optimism, but please not at the expense of realism. Here’s my take:
12/

We are in a much better place today than we were a month ago, but not yet close to the low level of transmission or at the predicted range of population immunity that would allow return to anything close to normalcy. 13/

Though our trajectory is currently terrific, we remain vulnerable to a potentially severe 4th wave given the large # of people remaining susceptible, the increasing proportion of more transmissible/severe B117 VOC & the easing of restrictions on activity across the country. 14/

Must be very cautious as we ease up on CoV-19 precautions & be prepared to reverse course promptly if we see trends change. Recognize the threat of complacency. 15/

We can minimize the risk for a large 4th wave by continuing to practice CoV-19 prevention measures & continuing to vaccinate as quickly as vaccine supplies allow. 16/

This means, for now, continuing to limit activities, wear well-made and well-fitting face masks, avoiding/limit time indoors with others outside the home & in crowded indoor spaces, improving indoor ventilation, & good hand washing. Did I say improving ventilation? 17/

Important to remember to isolate & get tested if you have symptoms of CoV-19, quarantine & get tested if you’ve been exposed, & let your close contacts know if you’ve been diagnosed or think you have CoV-19. 18/

If we manage to stay strong with CoV-19 prevention measures for just a few more months, further decrease transmission & continue to get more people vaccinated (key) we might avoid a severe 4th wave & have a much healthier & more normal summertime. 19/19

Whoops - should be when temperature and indoor relative humidity increase...