The media has been awash with good new stories about the early successes of some of the COVID-19 vaccines in the last couple of weeks. I am concerned that the next stage in the Pandemic could be a new problem of widespread transmission created by how we adopt and reaction to vaccine releases.

This concern is based on three assumptions that may or may not be true:

• That while the vaccines protect people from serious respiratory illness they do not protect people from infection and do not prevent transmission from vaccinated people.
• That a significant percentage of the population does not get vaccinated through a combination of concerns about the speed of the vaccine development, confusion about the range of vaccines, activity by anti-vaxxers and COVID conspiracy activists, and a misplaced confidence that lots of other people getting vaccinated will solve the problem.
• That once widespread vaccination programs start people, will become very complacent about social distancing, mask wearing, and hygiene.

If all these come true then I am worried that there is real scope for much greater community transmission and infection and we may get a new and different wave of problems. Wider transmission may also result in a larger group of people experiencing non respiratory problems. The relatively small number of positive cases in the current trials make it impossible to assess the risk of this with any degree of accuracy.

Let’s take a closer look at each of these assumptions

Vaccines and transmission

One simple thing that people need to understand here is that the surface of your lungs and the surface of the mucosa in your mouth and throat are outside of your body. This means that immunity inside your body is not the same thing as immunity at the surface of your respiratory system. That may seem a counterintuitive statement but think about your airway and your lungs like a balloon. If you blow air into a balloon then where that air goes is like the inside of your airways and lungs. If you try and apply a prevention or a treatment on the outside of the balloon then it has to get through the rubber to get to any bacteria or viruses on the inside of the balloon.

Any immunity conferred by a vaccine that you inject into the body has to get from the inside of your body to the surface of your respiratory system (through the rubber in our balloon analogy). This has been an issue for injections of vaccines against respiratory infections since these vaccines were invented.

This is particularly important with the COVID 19 infection which establishes itself in the upper respiratory system first which is the basis for the fact that infected patients can be infectious before they show any symptoms. This increases the likelihood that a vaccine will not prevent infection and transmission even if it prevents more serious disease which has been the main target of the clinical trials. None of the information that I have seen so far indicates prevention of infection but it is very early in the process and it may be that even if infection still takes place the viral shedding may be reduced. Never the less it is a plausible risk that transmission will still occur.

Vaccination Rates

In September 35% of Americans indicated they would not get vaccinated. This is affected by the politics in the USA but there is still significant uncertainty here in Australia with almost three in 10 Australians are at least somewhat hesitant about a COVID-19 vaccine, with 13% either highly hesitant or resistant. But the majority – 58.5% – definitely plan to get a vaccine once available. Historically we have seen social media attempts to sow discord on vaccination and this could bs stepped up for both financial gain and state sponsored political strategy. So there is a very real risk of 20-30% of the population not getting vaccinated.

Human behaviour

We have already seen evidence that people become less vigilant when they perceive that the risk of COVID is reduced. Lack of community transmission in Western Australia resulted in a change of public attitudes. Anecdotally I conducted small surveys of mask wearing in my area during lockdown and rates reduced as case numbers fell. It is very hard for people to maintain discipline for long periods to time, especially when the risk appears to have fallen significantly. It is highly likely that widespread vaccination programs will leave people with the view that the problem has bene solved and the levels of social distancing and hygiene are highly likely to fall in response.

If we combine all of these factors then we may see increased mixing of people, in a situation of high numbers of unvaccinated people, and transmission from vaccinated people who are completely unaware they are even infected, and therefore less likely to be tested.

I hope that some or all of this is not true but we need to be on our guard.

So what to do.

From a national perspective a clear and consistent communication program needs to go out on the vaccines and their efficacy and safety. This will boost vaccination rates. At the same time we also need to communicate that the vaccine is not a silver bullet. When I was a veterinarian involved in large scale vaccination programs with farmers we always had to guard against complacency. I would always approach this with the analogy of a set of scales. One one side of the scales was stuff that boosted immunity like vaccination, good nutrition, removal of environmental stresses, etc. On the other side of the scales were levels of infection which could be altered by hygiene levels, avoiding mixing of groups of animals, quarantine procedures, etc. Vaccination would certainly help tip the scales in the right direction but if the other positive measures were removed they could tip the balance the other way and overwhelm the vaccination. An animal that was exposed to high levels of virus and stressed by being cold or wet, or had poor nutrition would still succumb to infection. It is vital that we maintain strong social distancing and hygiene levels for a long time after a vaccine program is rolled out to make it effective as possible.

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