Vaccination of children might be effective in reducing influenza transmission in African settings – not only among this at-risk group but the community in general – found a South African study in The Lancet Global Health.
Seasonal influenza causes approximately 300,000–600,000 respiratory deaths globally annually, with the highest rates in sub-Saharan Africa. The, burden of mild influenza illness is higher in younger individuals (<5 years), and more severe illness occurs in extremes of age (<5 years and >60 years) and in individuals with underlying medical conditions, such as HIV.
The PHIRST population cohort study was conducted between 2017-18 in an urban and rural community in South Africa by researchers from the SA National Institute of Communicable Diseases and the University of the Witwatersrand, among others.
Dr Thinus Marais of pharmaceutical group Sanofi Pasteur, said this that because of non-pharmaceutical interventions like mask-wearing and social distancing, the numbers of flu cases reported in 2020 and 2021 were reduced. Now a resurgence is expected. “Flu vaccination is even more important now, given that simultaneous infection with flu and COVID can result in severe disease.”
The, burden of mild influenza illness is higher in younger individuals (<5 years), and more severe illness occurs in extremes of age (<5 years and >60 years) and in individuals with underlying medical conditions, such as HIV, the study noted. In addition to severe illness, milder influenza illness episodes might be associated with substantial effect on society, including absenteeism and loss of income.
“Influenza vaccination is recommended for individuals at high risk of severe outcomes—including people older than 65 years, pregnant women, and adults with HIV—but, due to restricted resources, influenza vaccine coverage remains low (<5%). Vaccination strategies targeting community influenza transmitters might be more cost-effective than risk-group based strategies, particularly in settings, such as South Africa, in which vaccination rates and care seeking in high risk groups remain low,” found the study.
“In the two communities in South Africa, the annual incidence of influenza infection was high and repeat infection within the same year was common. Rates of influenza infection and repeat infections were highest in children younger than 5 years and decreased with increasing age. Young children were more likely to transmit influenza.
“Approximately half of all infections were symptomatic and 14% were medically attended. Medically attended illness was more common in the extremes of age (individuals ≤18 years or ≥65 years). Asymptomatic individuals transmitted influenza, but at approximately half the rate of individuals with two or more symptoms.
Stellenbosch University professor of virology Wolfgang Presider said in the Sunday Times that schools are “breeding grounds” for flu, and children are a major factor in transmission and severe illness.
Preiser said: “The measures that contained COVID also worked against influenza transmission, especially school closures, as schools are thought to be breeding grounds from where influenza spreads to families and beyond.”
He recommends immunisation against flu every season, especially high-risk groups and those in close contact with them. COVID and flu vaccines could safely be taken concurrently, he added Vaccination can reduce the number of flu hospitalisations by 25%-39% and has also been shown to reduce overall mortality by up to 75% during flu seasons.
Study details
Asymptomatic transmission and high community burden of seasonal influenza in an urban and a rural community in South Africa, 2017–18 (PHIRST): a population cohort study
Cheryl Cohen, Jackie Kleynhans, Jocelyn Moyes, Meredith McMorrow, Florette Treurnicht, Orienka Hellferscee, et al.
Published in The Lancet Global Health
Summary
Background
Data on influenza community burden and transmission are important to plan interventions especially in resource-limited settings. However, data are limited, particularly from low-income and middle-income countries. We aimed to evaluate the community burden and transmission of influenza in a rural and an urban setting in South Africa.
Methods
In this prospective cohort study approximately 50 households were selected sequentially from both a rural setting (Agincourt, Mpumalanga Province, South Africa; with a health and socio-demographic surveillance system) and an urban setting (Klerksdorp, North West Province; using global positioning system data), enrolled, and followed up for 10 months in 2017 and 2018. Different households were enrolled in each year. Households of more than two individuals in which 80% or more of the occupants agreed to participate were included in the study.
Nasopharyngeal swabs were collected twice per week from participating household members irrespective of symptoms and tested for influenza using real-time RT-PCR. The primary outcome was the incidence of influenza infection, defined as the number of real-time RT-PCR-positive episodes divided by the person-time under observation. Household cumulative infection risk (HCIR) was defined as the number of subsequent infections within a household following influenza introduction.
Findings
A total of 81,430 nasopharyngeal samples were collected from 1,116 participants in 225 households (follow-up rate 88%). 917 (1%) tested positive for influenza; 178 (79%) of 225 households had one or more influenza-positive individual. The incidence of influenza infection was 43·6 (95% CI 39·8–47·7) per 100 person-seasons. 69 (17%) of 408 individuals who had one influenza infection had a repeat influenza infection during the same season. The incidence (67·4 per 100 person-seasons) and proportion with repeat infections (22 [23%] of 97 children) were highest in children younger than 5 years and decreased with increasing age (p<0·0001).
Overall, 268 (56%) of 478 infections were symptomatic and 66 (14%) of 478 infections were medically attended. The overall HCIR was 10% (109 of 1088 exposed household members infected [95% CI 9–13%). Transmission (HCIR) from index cases was highest in participants aged 1–4 years (16%; 40 of 252 exposed household members) and individuals with two or more symptoms (17%; 68 of 396 exposed household members). Individuals with asymptomatic influenza transmitted infection to 29 (6%) of 509 household contacts. HIV infection, affecting 167 (16%) of 1075 individuals, was not associated with increased incidence or HCIR.
Interpretation
Approximately half of influenza infections were symptomatic, with asymptomatic individuals transmitting influenza to 6% of household contacts. This suggests that strategies, such as quarantine and isolation, might be ineffective to control influenza. Vaccination of children, with the aim of reducing influenza transmission might be effective in African settings given the young population and high influenza burden.
Sunday Times article – Flu vaccine for kids could help curb post-Covid surge (Restricted access)
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Link between flu and heart complications grow stronger — large, 8-year study
Not a true reflection to compare COVID-19 and seasonal influenza mortality — JAMA viewpoint
Flu deaths in US already up 65% with unseasonal presence of influenza B virus
Flu jab has seasonal heart benefits and cuts pneumonia by 42%