Asymptomatic children are the main drivers of flu in SA - study
Traditionally, the flu vaccine in SA is recommended for high-risk groups but local researchers say this criteria should be extended to children, who are the main transmitters of flu viruses.
Normally, the elderly, pregnant women and those who are immune-compromised are targeted for flu vaccination, but in a study by Wits University and the Medical Research Unit, which was done in the North West and Mpumalanga, researchers found that many children with influenza viruses were asymptomatic but transmitted the flu to about 6% of household contacts.
“The high burden of asymptomatic influenza infections in the community, together with the fact that asymptomatic individuals transmit influenza to about 6% of household contacts suggests that asymptomatic individuals may be an important driver of influenza transmission,” says Prof Kathleen Kahn, senior scientist MRC/Wits rural public health and health transitions research unit, otherwise known as Agincourt.
Titled “Elevated community burden and asymptomatic transmission of seasonal influenza in an urban and a rural community in SA”, the 2017/18 study evaluated community burden and transmission of influenza in rural Mpumalanga and in urban Klerksdorp in the North West.
About 100 households were enrolled annually and followed for 10 months. Researchers performed nasopharyngeal swabs every two weeks on all household members, regardless of whether they showed symptoms. More than 81,000 samples were collected and tested for the presence of influenza, of which only 1% tested for influenza. Researchers found that in more than 79% of households, where influenza was detected, there was more than one person with flu.
Transmission was highest among children. Young children also experienced the highest burden of flu infection and symptomatic illness and were more likely to spread flu to their household contacts compared with other age groups.
The data shows that the proportion of symptomatic infections was higher in children older than five or 74% of infections was in this age group vs 39% in adults aged 19-44 years.
Dr Neil Martinson of Wits' Perinatal HIV Unit said this new data had “implications for the use of non-pharmaceutical interventions and vaccination strategies targeting children to prevent influenza transmission”.
In the study, about half of influenza infections were symptomatic, with asymptomatic individuals transmitting influenza to 6% of household contacts. Researcher said this data suggests that strategies, such as quarantine and isolation, might not be effective in controlling influenza.
“Thus, vaccination of children, with the aim of reducing influenza transmission, might be effective in African settings, given the young population and high influenza burden,” they said.
In SA influenza vaccination is recommended for individuals at high risk of severe outcomes, including the elderly, pregnant women, and HIV-infected adults.
They said in SA as a result of limited resources to procure vaccines, coverage remains low. The policy on vaccinations may therefore need to be relooked.
“Vaccination strategies that target community influenza transmitters, such as children, may be more cost effective than risk-group based vaccination strategies, particularly in settings such as SA where vaccination rates and care seeking in high risk groups remain low,” researchers noted.
A similar study under way in the same study sites aims to estimate the community burden and transmission of Covid-19.
Commenting on the Lancet global health where the study has been published, Harish Nair, professor of paediatric infectious diseases and global health, University of Edinburgh, wrote that the study “makes a valuable contribution to our hitherto poor understanding of respiratory viruses, like respiratory syncytial virus and influenza, that cause substantial disease burden in populations, particularly those at the extremes of age”.
“That the study was done in a high HIV-burden setting, SA, helps to understand disease transmission and the differential effect of respiratory infections in individuals with and without HIV,” said Nair.