COVID-19: A predictive model calculates how many days the protection of each vaccine lasts

In 2020, scientific researchers from different countries, companies and public institutions led a race to produce safe and effective vaccines against the coronavirus in record time. Today 80 vaccines are being evaluated in human clinical trials and 23 have reached the final stage of testing. But it’s still not clear what real protection people get from getting vaccinated. It’s also unclear how long this protection lasts, especially now that there are variants of the coronavirus that are more contagious and immunologically more difficult. Australian researchers have made a breakthrough to begin answering these critical questions for ending the pandemic.

Scientists carried out a study, which is still awaiting peer review in a trade journal, with Predictive modeling techniques to estimate the robustness and duration of immune protection conferred by seven different COVID vaccines. The results suggest that the more a vaccine protects immediately after administration, the longer its protection will last. However, they warn that Vaccination strategies should be adjusted to better address the problem of decreased immunity against the coronavirus.

The scientists, led by Miles Davenport of the Kirby Institute, part of the University of New South Wales in Sydney, Australia, based their model on the fundamental assumption that high levels of neutralizing antibodies – which are a sub – set of antibodies that can inactivate the virus – correlate with immune protection. This question had already been raised in previous research on reinfection in recovered Covid-19 patients and on the safety and effectiveness of the vaccine.

They used to conduct the study on data available on vaccines produced by the Pfizer-BioNTech companies in the United States and Germany, respectively; Moderna, from the United States; Sputnik-V, from Russia; Bharat Biotech, from India; Johnson & Johnson, from the United States; AstraZeneca; from England; and Coronavac from SinoPharm, China. They were able to delineate the state of the levels of neutralizing antibodies generated by each of the vaccines over 250 days.

The researchers then compared these trajectories to those of recovered COVID-19 patients who had natural immunity. In addition, modeled how lower antibody levels might behave against novel coronavirus variants. They also used convalescent sera as a benchmark to standardize vaccine data, which in their original state came from a diverse set of tests and therefore were difficult to collect.

Researchers they hope the modeling study “will help develop vaccination strategies to control the future trajectory of the pandemic.” One issue to consider in immunization plans is that protection against COVID-19 disease is not the same as protection against infection itself.

When the researchers analyzed the levels of neutralization produced by each vaccine and fed the numbers into their model, they found that protection against severe Covid-19 remained stable, but protection against coronavirus infection declined significantly. They found that the degree of decrease in protection conferred by the vaccine depended on the initial intensity of the neutralizing antibody response.

The Australian study is also heightening concern about the risk of more cases of becoming infected with the newer variants of the coronavirus, particularly those in England, South Africa and Brazil. Those The new variants are more difficult to neutralize than the original virus that was detected in Wuhan, China in January of last year.

Several studies have already documented how the effectiveness of the first generation of Covid-19 vaccines – even at their strongest, in the days following vaccination – is reduced against the South African variant in particular: they provide protection but not as much. than before. demonstrated by testing with the parent virus.

The predictive model of Australian scientists took into account the question of variants. He suggests that variants pose a greater threat to vaccines with lower initial efficacy against the parent virus. If the initial efficacy of a vaccine is, for example, around 70% and the neutralization levels of the vaccine are reduced five times by the presence of a new variant, researchers predict that the efficiency will drop to just 25%.

Another result that the work contributed is that there would be differences in the levels of neutralizing antibodies depending on the vaccine applied. The Pfizer and Moderna vaccines were the most effective, with an initial efficacy of 95% which did not drop to 50% until around day 200. The Sputnik V vaccine maintained an efficacy of 70% at 150 days and 50%. to 125 days.

Meanwhile, the Johnson & Johnson and AstraZeneca vaccines had an initial efficacy of 67 and 62% respectively, but reached the 50% protection mark around day 50. At the opposite extreme was Sinopharm’s Coronavac vaccine, which is given in Chile, among other countries. This vaccine had an initial efficacy of 50 percent, but they found protection after two or six months of administration according to the modeling.

However, the results do not mean that some of the licensed vaccines should be excluded. They admit that the study is predictive, not prescriptive, and that it is based on hypothetical means drawn from available data on convalescent sera.

It should also be noted that recent work on patients with Covid-19 in Singapore has suggested that the duration of the neutralizing antibody response varies from individual to individual, with a very small fraction experiencing very long persistence. and another fraction, no antibody at all.

Consulted by Infobae, Víctor Romanowski, researcher at Conicet and vice-president of the Argentinian Society of Virology, said the Australian study “is still under peer review. Therefore, it does not have the approval of long-term experimental evidence that could allow to evaluate or adjust the predictions / explanations of the theoretical model ”.

Dr Romanowski mentioned that “It is interesting to be confronted with the study of models which make it possible to predict from simple data to obtain the level of protection which can be granted to a candidate vaccine. The reality is that there is not yet enough evidence on the correlation of protection between the data, based on the levels of neutralizing antibodies as markers of the immune response, and the effectiveness of the vaccines under study ” .

According to researcher Conicet, Australian scientists “base their statements on the levels of neutralizing antibodies, which are one of the markers of the immune response and of great interest”. He added: “I consider that they forget about the cellular response and the memory of the immune system, which are also important when it comes to a pathogenic infection against which the vaccine response was initially elicited. Other studies in volunteers from clinical trials of vaccines do not seem to confirm these very negative predictions with respect to some of the vaccines already applied ”.

For his part, Humberto Debat, researcher in virology at the National Institute of Agricultural Technology (INTA), commented Infobae about the study in Australia: “The attempt to study two aspects of a potential for standardization and difficult prediction is interesting: the correlate of protection based on neutralization tests, and the modeling of the decrease in immunity and antigenic drift in the medium term and its association with the efficacy of vaccines. Roughly, the authors suggest that neutralization tests are good predictors of vaccine protection. They also warn that the drop in immunity at 250 days would be significant and permissive to infections, but likely resistant to serious disease.

Infographic: Marcelo Regalado

KEEP READING: