In regions where the Delta variant of the new coronavirus is prevalent, the interval between doses of vaccine against covid-19 needs to be less than 12 weeks for effective control of the pandemic. This is suggested by a model developed by the Center for Mathematical Sciences Applied to Industry (CeMEAI) from preliminary data on the efficacy of AstraZeneca’s vaccine for the Delta variant.
CeMEAI is a Research, Innovation and Diffusion Center (CEPID) of FAPESP (Research Support Foundation of the State of São Paulo) based at the University of São Paulo (USP), in São Carlos.
The tool is described in an article published in the scientific journal Proceedings of the National Academy of Sciences (PNAS). The technology – created by the ModCovid-19 group, which includes researchers from the State University of Campinas (Unicamp), the Getúlio Vargas Foundation (FGV) and the University of São Paulo (USP) – projects a safe and ideal time between doses to control the pandemic, based on vaccine efficacy data.
ModCovid-19’s work shows that vaccines with less than 50% efficacy in the first dose need a shorter application interval than vaccines with higher efficacy rates. Fueled by previous studies on the effectiveness of immunizing agents, the technology indicates when it is possible to postpone doses and when the maximum possible protection is achieved.
“The algorithm itself decides when it is best to apply the second dose, taking into account the first one, in order to control the pandemic as quickly as possible”, explains Paulo José da Silva e Silva, study co-author and professor at Unicamp, in an interview with Communication Advisory at CeMEAI. Therefore, the tool available online can help in decision making during the immunization process of the Brazilian population and other countries.
The professor remembers that, when the article was written, in February 2021, the main question was whether it would be worth delaying the second dose and what is the safest way to do this, given the limited amount of doses. In this sense, the study was based on the AstraZeneca vaccine and concluded that the difference in the percentage of effectiveness between the first dose and the second was very small and, therefore, it would be worth waiting and vaccinating more people with the first dose.
Now, with the advancement of the Delta variant in some regions of Brazil and the world, vaccination strategies can be revised based on this model.
“With the publication of the article in PNAS, we hope that the technology we have developed will become more accessible and can reach many countries and decision makers. We leave the code fully available on the internet and we are also available to help anyone who wants to use it. Our work develops and implements the methodology that can analyze the situation in different locations. We developed a model that is not just for Brazil, it is a contribution to science and is a technology that can be used in the future, not just for COVID-19”, concluded Silva.
The article Optimized delay of the second COVID-19 vaccine dose for ICU admissions can be read at: www.pnas.org/content/118/35/e2104640118.