Abstract INTRODUCTION The percentage of asymptomatic COVID-19 cases worldwide is estimated at 18–50%; 53% in Cuba specifically, and 58% in Havana, the Cuban capital and the 2020 epicenter of the country’s COVID-19 epidemic. These figures, however, do not represent the transmission capacity or behavior of asymptomatic cases. Understanding asymptomatic transmission’s contribution to SARS-CoV-2 spread is of great importance to disease control and prevention. OBJECTIVE Identify the epidemiological implications of asymptomatic SARS-CoV-2 infection in Havana, Cuba, during the first wave of the epidemic in 2020. METHODS We carried out a cross-sectional study of all confirmed COVID-19 cases diagnosed in Havana, Cuba, from March 16 through June 30, 2020. The information was obtained through review of the standardized form for investigation of suspected and confirmed cases. Examined variables included age, sex, occupation, case type and source of infection. Cases were divided into asymptomatic and symptomatic groups, and transmission was characterized through the creation of a contact matrix. Analysis was carried out in Epidat and R. RESULTS We studied 1287 confirmed cases, of which 57.7% (743) were asymptomatic, and 42.3% (544) were symptomatic. Symptomatic presentation was the most common for both imported and introduced cases, while asymptomatic presentation was more common in autochthonic cases and infections from an undetermined source. Asymptomatic infection was more common in groups aged <20 and 20–59 years, while symptomatic infection was more common in those aged >60 years. In the contact matrix, 34.6% of cases (445/1287) were not tied to other cases, and 65.4% (842/1287) were infectious–infected dyads, with symptomatic–symptomatic being the most common combination. The majority of primary cases (78.5%; 1002/1276) did not generate secondary cases, and 85.6% (658/743) of asymptomatic cases did not lead to other cases (although one asymptomatic superspreader led to 90 cases in a single event). However, 63.2% (344/544) of symptomatic primary cases generated secondary cases, and 11 symptomatic superspreaders spawned 100 secondary cases in different events. CONCLUSIONS Asymptomatic SARS-CoV-2 infection was the most common form of COVID-19 in Havana during the study period, but its capacity for contagion was lower than that of symptomatic individuals. Superspreader events under specific conditions played an important role in sustaining the epidemic.

ABSTRACT Vaccination is one of the most cost-effective interventions for control of communicable diseases. This health achievement could founder if measures are not taken by health systems to prioritize immunization, increase vaccination rates and educate health professionals to address public concerns about vaccine safety and efficacy. Parents’ refusal to vaccinate their children directly affects public health, because it puts both individual and group immunity in danger; immunization coverage is effective only when high population coverage is attained. The growing number of antivaccination (antivaxxer) groups around the world is alarming, contributing to falling vaccination rates. Troubling consequences include disease outbreaks in several countries globally and in our hemisphere. This article looks at the history and features of antivaxxer movements around the world and proposes ways the Cuban health system, through its National Immunization Program, can address dangers for the population associated with potentially negative influences of social-network antivaxxer campaigns. The paper underscores the role of mass and social media, health professional training and sustained competence, and the importance of a vaccine-related adverse events surveillance system.

INTRODUCTION Cuba has implemented an effective National Immunization Program since 1962. The schedule, administered primarily to children, comprises 11 vaccines (8 domestically produced) protecting against 13 diseases. In 1999 Cuba launched a national vaccine adverse event surveillance system to monitor and assess the safety of the immunization program, its vaccination procedures and the products administered. OBJECTIVES Describe adverse events following vaccination reported in children aged <16 years in Cuba from 1999 through 2008. METHODS A retrospective descriptive study was conducted of adverse events following vaccination reported from January 1999 through December 2008. Variables used: year, number of adverse events, province, type of vaccine, type and severity of adverse events (common minor, rare, severe), vaccination program errors, number of deaths, and final results of investigations of severe events. Percentages and rates per dose administered were calculated. Adverse event rates were calculated per 100,000 doses administered and by percentages of individual effects among events reported. RESULTS A total of 45,237,532 vaccine doses were administered, and 26,159 vaccine-associated adverse events were reported (overall rate: 57.8 per 100,000 doses). The group aged 0-5 years reported the highest rate of vaccine-associated adverse events (82/100,000 doses). The DTwP vaccine exhibited the highest rate of adverse events. Common minor events were: fever (17,538), reactions at injection site (4470) and systemic side effects (2422). Rare events (by WHO definition) reported were: persistent crying (2666), hypotonic-hyporesponsive episodes (3), encephalopathy (2) and febrile seizures (112). Severe events included: anaphylaxis (2), respiratory distress (1), multiple organ failure (1), sudden death (1), vaccine-associated paralytic poliomyelitis (2), toxic shock syndrome (3), and sepsis (1). The 10 deaths and 3 cases of disability were investigated by an expert commission, which concluded that 8 of the 13 severe events were vaccination-related. CONCLUSIONS Low rates of severe vaccine-associated adverse events observed in this study underline the low risk of vaccination relative to its demonstrated benefits in Cuba. Decision-making for the continued success of the National Immunization Program is supported by reliable information from comprehensive national surveillance with standarized reporting, along with multidisciplinary expert analysis of rare and severe adverse events and program errors.