What is the reactive vaccination strategy?

The numbers of the epidemic are increasing. Even if vaccination coverage is high in France, there are still people who refuse to be vaccinated. How to convince them? A team of French researchers had the idea to model the reactive vaccination strategy to assess whether it can increase the number of people vaccinated in France.

As of March 22, 2022, 79.5% of French people have a complete vaccination schedule and 58.5% have received a booster dose. However the virus continues to circulate and the number of daily cases is rising again in recent weeks. The effective R was back above 1 for the week of March 7, signifying that the virus is actively spreading. In a context of lifting health restrictions, fears of a resumption of the epidemic and the appearance of new variants are legitimate. Although imperfect, vaccinating as many people as possible remains an effective weapon against the spread of SARS-CoV-2, especially against severe forms of the disease. How? ‘Or what? convince the most recalcitrant to vaccinate? French researchers propose an original solution: the reactive vaccination strategy. This involves offering the vaccination to those around an infected person (home, workplace, school). The reactive vaccination strategy is already used in other contexts, such as during epidemics of meningitis. The results were published on March 17, 2022 in the prestigious journal Nature Communication.

A statistical model

The researchers used INSEE data to build their model. It has the sociodemographic characteristics, social contacts, and professional situations of a medium-sized French city, but also the characteristics of the disease, vaccination coverage, and vaccine efficacy. From this model, the authors imagined various scenarios of epidemic dynamics. In most scenarios, the impact of implementing a reactive vaccination strategy is beneficial.

Even more effective if vaccination coverage is low

Let’s take the example of a model where vaccination coverage is around 45% and where the virus is actively circulating. In the case of a vaccination campaign mass, the reduction in the number of cases over two months is 10%. In the case of a reactive vaccination strategy added to a mass vaccination campaign, this figure increases to 16%.

The strategy is all the more effective when vaccination coverage is low. In fact, if vaccination coverage is high, most of the infected person’s environment is already vaccinated. However, even in this scenario, reactive vaccination has benefits. It has been observed that people who were initially refractory to vaccination were somewhat less so after being exposed to the virus.

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