Covid-19 is already endemic in 75% of the world’s countries. This means the virus is in those populations to stay. They will continue to have their healthcare systems overwhelmed and experience big seasonal surges in numbers for the next year or two. Their economies will struggle. Australia has an opportunity to remain relatively free of the virus – it is not endemic here (yet). We start community vaccination in March.
Herd immunity versus community resistance
Herd immunity is a loose term that is used overly optimistically – the “herd” is seldom immune until at least 90% of people are vaccinated with a very very effective vaccine such as the measles vaccine that is 95% effective. I prefer to use a term such as community resistance.
Community resistance is a function of multiple factors such as:
1 the infectiousness of the virus – how many people get the infection from one infected person – this is know as R0
2 the immunisation rate
3 transmission by people before they get symptoms
4 what the antibody produced by the vaccine actually blocks
5 whether the immunity created kills the virus or just slows t reproduction
6 importation of infected cases from outside the country
7 societal factors such as social crowding, city living, hand washing, mask wearing, etc
8 The average R0 is quoted as about 2.5 but in a big city it can be 8. This means one person in a big city is likely to give it to 8 others. Picture New York when the virus hit. It would start with one infective person in an area. In 3 to 5 days there would be 8. Another 3 to 5 days and it’s 64. Another 3 to 5 days and it’s 512 people infected, and so on, 4,000, 32,000. This is the central issue – the pandemic is still growing exponentially around the world while human thought and political understanding grows in a linear fashion.
Bear in mind that 50% of transmission occurs before the infectious person gets symptoms. Covid-19 starts by quietly replicating in our bodies. It ruptures a few cells and we become contagious to others. Later on, and depending on how many target ACE2 receptors we have on our lung and blood vessel cells, it can produce a storm of cell destruction . It kills by heart failure and lung failure and will leave survivors with a range of long term slow killers like inflamed blood vessels (vasculitis), chronic lung disease, and even Parkinson’s disease.
Community resistance can be measured by infection rates, complication rates and death rates. It’s therefore a very relevant outcome measure of what matters when comparing vaccines.
The vaccines will have a significant impact, but new strains will evolve, making the vaccination programme one of tail-chasing year by year as we develop new vaccines for new strains. The Pfizer vaccine is very effective, giving 95% prevention ( 20 times more likely to get the infection if you are not vaccinated). But it is expensive at about US$30 per shot. It binds to the foot of the virus and stops it binding to the ACE2 receptors on our cells. See my article April 23rd 2020. We don’t know it’s long term effectiveness and whether viral evolution will render it just a temporary fix, and that applies to all the vaccines. In Australia our community programme will roll out using two shots of the much cheaper Oxford University vaccine (about US$3 a shot). My guess is that this vaccine slows viral replication and massive cell destruction. Just under 6,000 people were vaccinated in the study and another similar sized group were not vaccinated. During the follow up period of only 4 months in the UK and Brazil, there were no deaths and no hospitalisations in those vaccinated, compared with 10 hospitalised and one death in the control group. This Oxford – Astra Zeneca vaccine therefore significantly increases the survival rates of those who are exposed to the virus after vaccination but will be less able to create classical immunity. Hence my emphasis on community resistance as a better measure of our success. Continuing mask wearing, hand hygiene, avoiding crowded events and social distancing lessens the number of people an infected person will give the virus to (the R0). Social interventions will remain an important part of our National strategy. At Aberfoyle Park Medical Centre we plan to start vaccinating in mid to late February using the same “safe surgery” approach that we did last year, with a separate space for vaccinating. I will publish details later.
Predictions for 2021
The World in general
Worldwide at the end of April 2020 there were 100,000 new cases per day. Eight months later, at the end of December, there were seven times the daily new cases – 700,000 per day. If the trend of the known figures from the end of March 2020 to the end of December 2020 are extrapolated to the end of February 2021 the world could be seeing 1,000,000 new cases each day. The daily new cases could double by the end of April 2021. The exponential growth in infections will continue and proportionately increases the numbers of overseas travellers who will have the virus when they fly in.
I have appended my calculations below along with a graph of worldwide daily new cases.
Australia in particular
In the 6 months from the end of April to the end of October, 1% of incoming overseas travellers carried the virus. This is a total of about 1200 people who brought the virus into Australia. Despite the use of self isolation, quarantine hotels, a 99% reduction in incoming flights, and significant community restrictions, those 1200 cases over 6 months led to an additional 19,000 cases Australia-wide.
In August and September with incoming international passengers limited to around 15,500 per month, there was one case in every 300+ incoming international passengers. In October, with 23,442 incoming passengers, there was one case in every 65 passengers. The safe and manageable limit of incoming passengers was exceeded in October – our quarantine systems failed. The systems keep failing because they are not robust.
Currently, every incoming international flight carries one or two people with the infection. Predictably, some of the new cases break quarantine and spread the infection into the community. I do not know why our Chief Medical Officers and Politicians continue to express surprise.
As it stands, 2021 is likely to be the year of increasingly frequent and prolonged periodic lockdowns for us all. Our problem is how to manage the people who bring in the virus. They must not be allowed to float around the community when they are supposed to be in a hotel. In Korea they use a phone app that shows when a person-at-risk is nearby. It warns other people of the potential risk.
Australia has a window of opportunity to be one of the few countries in which the virus can be held at check. This will only happen if we improve our border control to lessen the “leakage” created by the current quarantine policies. Vaccination is our backup approach, and we start within weeks.
Terry Rose – January 14th 2021
Select, copy and paste the links into your browser.
Worldometer – daily new cases
Graph of new cases worldwide
‘This shows actual numbers and an averaged curve with a formula for future projections
The graph shows the actual number of new cases per day worldwide at the end of each month from March 2020 to the end of December 2020. It also shows an average curve (regression line) along with a formula to calculate the expected numbers in the future. The R squared value is high and demonstrates good correlation between the actual and averaged graphs. Predictions can be made using this graph and formula. X is the number of months from 31/3/2020. Y is the number of new cases per day for the whole world.