Why we are where we are with our high Covid-19 rates …

Dr. Claire Donnelly is a Consultant Medical Doctor with expertise in infectious diseases and an MSc in Epidemiology

I want to try to explain from an epidemiological point of view how NI is approaching a cliff with Covid 19. Professor Devi Sridhar has used the boiling milk analogy to explain this very well. At first it starts to boil slowly and it seems like not much is happening. As you approach boiling point and turn the cook away from your eye, it can boil over in seconds. There we are now with Covid in NI. We have reduced the restrictions, but the number of cases is still high. Increases in cases could and likely will happen quickly. On December 17, the NI Covid Dashboard reported 656 new cases, with 3531 cases diagnosed in the last 7 days.

The exponential increase in the number of cases can be explained in different ways. Lots of people are familiar with Ro. However, I find it more useful to understand doubling time. This is the number of days it takes to double the number of cases. The rapid exponential increase is illustrated by NI Covid’s September and early October numbers before a number of restrictions were in place. On September 30th, 424 new cases were displayed on the NI Covid dashboard, and on October 7th that number rose to 828 new cases per day. As of October 7, 4,417 cases were diagnosed in the last 7 days, compared to 2,049 in the previous 7 days. The number of cases has more than doubled within 7 days. If this had continued without restrictions or a change in people’s behavior, the number would have continued to grow exponentially. To put this into numbers, without a change in people’s contacts, 4417 could have climbed to over 8,000 and then to 16,000 and so on. It’s likely that many people would have stopped going out and exponential growth slowed, but these numbers are what would happen without change.

No health system in the world can cope with these numbers, and even countries like Germany with more than five times the intensive care capacity like NI had to introduce restrictions before Christmas.

Mathematical models have been used to monitor, predict, and control public health policies throughout the pandemic. It is important that people understand the limits of models. They try to predict what will happen based on various factors including people’s behavior and the number of interactions they have with other people. Assumptions are made about how people will interact in the run-up to Christmas. However, there isn’t any data that tells you exactly how the people of NI will behave before Christmas during a pandemic. These dates will be available after Christmas. Collateral information like mobility data helps, but relying on such assumptions overestimates the accuracy of models as a forecasting tool. If our contacts are similar even at the end of September, our numbers will increase by a high value and we could easily surpass the record numbers we saw in October in a short period of time. The milk could literally boil over before you turn off the stove.

Sometimes it seems like few people in NI are complying with Covid’s guidelines, as only the non-compliant people are highlighted in the media. Ro was around 3 when the pandemic started. It has often been around 1 in the past few months and always well below 2. This shows that many people are following the guidelines.

I think putting restrictions in place after Christmas is a very risky strategy. It is very likely that before that the numbers will soar to high levels that could overwhelm health care in NI. We won’t know for sure until January, but that’s the problem with trying to predict the future with a mathematical model based on human behavior.

The higher the numbers go over Christmas, the longer and tougher the New Year restrictions will be to bring the numbers down. For people who say this is just the flu. It is not. I’ve worked on infectious diseases for over 20 years and I’ve been a doctor for over 25 years, and Covid is not like the flu.

My interpretation of the guidelines is that Christmas is a time to support our families and friends. Most effective for many people is not to meet them face-to-face and virtually. However, for many people struggling with the limitations and loneliness that the pandemic has brought, the guidelines allow a small number of contacts to be made.

My Christmas dinner will only be in the household with my family members. I’m going to wish my parents a social, freestanding, outdoor Christmas and won’t see them until we’ve all got the vaccine.

Photo by Queven is licensed under CC BY-NC-SA

This is a guest slot to provide a platform for new writers, either as a stand-alone piece or as a prelude to becoming part of the regular Slugger team.

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