According to the Doherty model, we need to start vaccinating people in their 20s and 30s. Epidemiologist explains why

Last week, the federal government announced that 70% of people over the age of 16 would need to be vaccinated to relax COVID-19 restrictions.

This week, the Doherty Institute in Melbourne released a model to illustrate this point. The National Cabinet has asked the Doherty Institute to model the impact of increased vaccination rates on Australia's way out of the COVID pandemic.

The collaboration created an impressive portfolio of models that allowed them to assess the impact of an outbreak under a range of infection control situations. The model can be adapted to explore relaxations of specific restrictions or changes in conditions, for example, if the main variant changes, or our response is more effective or less effective than expected.

They found that vaccinating 70% of more than 16% of people would allow reduction of restrictions in the event of an outbreak, while reaching 80% would mean significant relaxation and possibly no lockdown.

The continued need for intervention highlights how difficult it is to manage Delta variants compared to previous strains. Even if 80% of the population over the age of 16 are vaccinated, a certain degree of active control in an outbreak environment is still required, albeit with mild restrictions.

The modeling uses Australian data collected from across the country since August last year. This includes data on the "transmission potential", which is actually the average number of people who may be infected by an infected person. With varying degrees of public health response and people’s compliance with restrictions, the modeler is able to estimate this reproduction rate of the virus to understand the conditions required to reduce the transmission potential to below 1 and keep it there, so The infection will not exceed a manageable level.

The modeling forecast was extended by six months. Considering the rapid changes in this epidemic, this is actually a relatively long time frame. In addition, the parameters began to become unreliable, so the reliability of predictions decreased. Modeling is a very sensible best guess, but there are many uncertainties. The value here is to compare different scenarios to map the most strategic route, not to predict the specific number of ICU beds or cases.

This model provides us with guidelines for the level of vaccination coverage required to control the virus. The current 80% score of eligible people provides a certain degree of protection, which is expected to get rid of our current cycle of lock-in. It also emphasizes that time is of the essence-we need to get there before new variants appear.

If we stay in the current predicament, we may embed community communication in other states and repeat the situation in New South Wales across Australia.

As the vaccination rate increases, the demand for strict restrictions decreases, so vaccination is our way out of the predicament.

Why pay attention to young people?

So far, Australia’s rollout has focused on those most likely to have serious consequences from the disease, including elderly Australians, to protect them and our healthcare system from being overloaded.

But in order to reach the vaccination goal in the most effective way, this model proves the value of shifting our current focus to reducing transmission.

Our highest transmission rate and case rate occur in people 20-39 years old. This group is the most mobile. They tend to interact and interact with other people the most, so on average, they have the closest contact. Many people live in shared houses, with young families, which account for a large part of the labor force, especially basic workers. Professor Jodie McVernon of the Doherty Institute said that especially those 20-29 years old are the "peak period of transmission."

It is very important that we start to vaccinate people aged 20-39, because this method can better benefit our vaccination costs.

Vaccinating this group will not only protect them, but also the entire population, including those who cannot be vaccinated. People who are vaccinated are unlikely to be infected, and even if they are infected, they are unlikely to be infected. The Doherty Institute’s technical report on modeling shows that the combined effect is that the transmission risk of AstraZeneca and Pfizer has been reduced by 86% and 93%, respectively.

Professor McVernon said that vaccinating as many people as possible between 20-39 years old can double the protection over 60 years old and protect everyone else, making it the fairest strategy we have launched at this stage.

Why not include children?

The Doherty Institute is not required to consider vaccinating people under 16 years of age, so in the model, children are considered unvaccinated. Therefore, their protection and the protection of schools from the impact of the epidemic depend on adults, especially parents, who reach the 80% target.

The risk here is that if the virus does enter schools, it may cause a large-scale outbreak and spread quickly to the entire school-as we are currently seeing in Queensland. More robust public health interventions may still be needed to control the epidemic.

Over time, we must monitor this closely, as the children’s COVID vaccine trials continue to help us weigh the risks and benefits.

This week, ATAGI recommends that children aged 12-15 years who are Aboriginal or Torres Strait Islander, live in remote communities or have potential health problems should give priority to vaccinations.

As the overall vaccination rate rises, we need to pay attention to areas with low vaccination coverage. If the virus enters, we may still see a certain degree of local transmission, which needs to be restricted. But in these cases, the restrictions will be more localized and targeted rather than entire cities or states.

Australia’s Chief Medical Officer, Professor Paul Kelly, said very well at the press conference on Tuesday: We can achieve a "soft landing" that other countries cannot achieve. The model tells us that when we reach 80% adult vaccination coverage, we can avoid the huge wave of infections we are trying to prevent.

Unlike the United States, where cases have reached a peak again after the reopening of the United Kingdom, or the number of cases and hospitalizations are increasing, we can take advantage of our past success in epidemic control and overcome difficulties without seeing a wave of true internationalization.