By Walkiria Juanes Sanchez on December 21, 2020
Foto: Ismael Batista
How is COVID-19 transmitted between asymptomatic persons? How many cases remain undetected? How large is the number of asymptomatic people with infection? What has the immune response been to the coronavirus in the Cuban population? What are the principal risk factors for getting this infection and what has been the clinical course of those who are infected?
These are some of the questions to which the Nation Investigation of Incidence and Prevalence of Infection by SARS-COV-2 is seeking to find clear answers. This study is the first of its type, not only in Cuba, but in the whole Western Hemisphere, according to Dr Vivan de las Mercedes Noriega Bravo, specialist in Epidemiology and head of the team of researchers. The study is not only a response to an appeal of the World Health Organization (WHO), but primarily one of the actions taken by the Cuban government towards control of the pandemic and to further inform the Cuban people about the decisions being made in the transition to recovery and normality in Cuba.
The Epidemiological Dynamic In a Successful Confrontation
Dr Noriega Bravo explained that, until the Cuban study began, Spain was the only country where a similar study had been done – a research study of the type called a prospective cohort study. Statistical and mathematical analysis can facilitate scientific understanding of the phenomenon of asymptomatic infected people, since the research reveals that, among a presumably healthy population, there are some with detectable antibody titers and immunological memory indicating that they have been in contact with coronavirus without developing symptoms. These people were not found on routine epidemiological surveillance, since they were not contacts of confirmed cases, or of international travelers, and were not in any high-risk group; this represents a risk that the health system needs to respond to.
Knowledge of the national epidemiological dynamic is crucial in order to adopt efficient measures for containing the pandemic. Because of this, Dr Noriega Bravo explains, the primary goal of this research was to estimate the prevalence of SARS-COV-2 infection in the country. Then the immune responses and the accumulated incidence will be analyzed according to the principal sociodemographic characteristics, and it will be possible to determine to what extent there are individuals with asymptomatic or subclinical infections, and what are the fundamental traits of those in this situation. The study includes identification of the most important risk factors for infection, and the evaluation of changes in morbidity, as well as the presence of antibodies.
From the Epidemic Period to Recovery
Taking the standard protocol suggested by WHO as a basis, along with the experience of Cuban experts, a representative sample of the Cuban population was chosen, with random selection of people from all 15 provinces, except Isla de la Juventud. 260 primary care doctors’ offices were randomly selected in 70 areas, and 5 families were chosen at random from each of these for a total of 1,300 families in the third selection round, a process including only presumptively healthy people of all ages, excluding only babies under 15 days old at home; the total was 4000 persons. Of these 3896 were followed through four evaluations, and the analyses of the information obtained is now being processed, points out Noriega Bravo.
The evaluations were done approximately every 28 days, which is two incubation periods. In each of these laboratory studies were done, with a questionnaire to explore different variables. In the first evaluation, a PCR (Polymerase Chain Reaction) test was done to detect presence of virus, and in the second, third, and fourth evaluations IgG antibody titers against SARS-COV-2 were determined , suing the suma system developed by Cuban biotechnology. (IgG antibodies are proteins that recognize, capture and block the virus.) The last evaluation also included PCR testing to determine not only how immunological memory had functioned, but how people had progressed over time.
The study began during the epidemic phase, and will finish in the phase of recovery – that is – the 4 evaluations will take place in time during the phases I- III set out in the national plan for confronting COVID-19, taking into account that, at a given moment in the study, different provinces may be in different phases.
Preliminary Results
Preliminary results show that part of the presumed healthy population has been infected with the virus, as indicated in the first evaluation as active infection by PCR testing and afterward, as prior or non-recent infection detected by the presence of IgG antibodies against SARS-COV-2, Dr Noriega Bravo states. She also points out that the presence of people with IgG antibodies indicates that part of our population has been in contact with the virus and has not developed signs of illness. Roughly 90% or more of these people have been asymptomatic at the time they were studies. We may approximate that when the first evaluation was done, around May 16, 89.7% of the total number of those with active infection were asymptomatic, and by the middle of August 88.8% of those previously infected also were, she said. Only a small fraction of those infected developed symptoms after being evaluated – had they done so they would have been pre-symptomatic. Most remained asymptomatic, constituting therefore a risk for the general population. Many of those who were infected but asymptomatic were in geographic regions with only scattered cases of confirmed COVID-19, and in population groups where no cases of illness had been known.
The preliminary results of this study call to our attention the importance of individuals with asymptomatic infection, especially now in our “new normal.”
The Commitment of Cuban Science
The researchers are a central group of experts, together with a work-group for this project of the Ministry of Public Health, and also groups of primary care professionals who work in different provinces and municipal areas of the country.
There is great anticipation for these results at the international level, since the response of the Cuban study population has been magnificent, with a high percentage of participation among those surveyed. “Our group of researchers is committed to continue working along these lines in order to continue to contribute scientific evidence toward greater effectiveness in decision-making,” Dr Noriega Bravo maintained.
Source: Granma, translation Resumen Latinoamericano, North America bureau