Pneumococcal infections are a major cause of communicable disease morbidity and mortality worldwide.1O'Brien KL Wolfson LJ Watt JP et al.Burden of disease caused by Streptococcus pneumoniae in children younger than 5 years: global estimates. The highest burden of disease is found in young children, older adults, and immunosuppressed people. Low-income and middle-income countries, including those in Africa, have high burdens of pneumococcal disease, with associated high mortality rates, due to an accumulation of factors conducive to high and persistent pneumococcal carriage and transmission, including high-density living conditions, poverty, and high HIV seroprevalence.1O'Brien KL Wolfson LJ Watt JP et al.Burden of disease caused by Streptococcus pneumoniae in children younger than 5 years: global estimates., 2Troeger C Forouzanfar M Rao PC et al.Estimates of the global, regional, and national morbidity, mortality, and aetiologies of lower respiratory tract infections in 195 countries: a systematic analysis for the Global Burden of Disease Study 2015. Pneumococcal infections cause both non-invasive and invasive disease. Invasive pneumococcal disease refers to more severe diseases such as bacteraemia, sepsis, meningitis, and osteomyelitis, in which bacteria penetrate the body's defensive barriers and enter a sterile site (eg, blood, cerebrospinal fluid, pleural fluid, joint fluid, or pericardial fluid). Routine childhood immunisation with pneumococcal conjugate vaccines (PCV) has changed the epidemiology of invasive pneumococcal disease in many high-income countries.3Feikin DR Kagucia EW Loo JD et al.Serotype-specific changes in invasive pneumococcal disease after pneumococcal conjugate vaccine introduction: a pooled analysis of multiple surveillance sites. Vaccination of infants with PCVs has been introduced in many African countries but the burden of pneumococcal disease and the impact of PCV in an African setting has not been comprehensively evaluated.Following the introduction of the 13-valent PCV (PCV13) in Malawi in November, 2011, Naor Bar-Zeev and colleagues4Bar-Zeev N Swarthout TD Everett DB et al.Impact and effectiveness of 13-valent pneumococcal conjugate vaccine on population incidence of vaccine and non-vaccine serotype invasive pneumococcal disease in Blantyre, Malawi, 2006–18: prospective observational time-series and case-control studies. examined the impact of the vaccine on vaccine-serotype and non-vaccine-serotype invasive pneumococcal disease among vaccine-age-eligible and vaccine-age-ineligible children and adults. In The Lancet Global Health, Bar-Zeev and colleagues4Bar-Zeev N Swarthout TD Everett DB et al.Impact and effectiveness of 13-valent pneumococcal conjugate vaccine on population incidence of vaccine and non-vaccine serotype invasive pneumococcal disease in Blantyre, Malawi, 2006–18: prospective observational time-series and case-control studies. describe data from laboratory-based surveillance at a government hospital in Malawi from 6 years before and 7 years after the introduction PCV13. From this long-term hospital surveillance, conducted after the introduction of antiretrovirals in an area with high disease burden and high vaccine uptake,4Bar-Zeev N Swarthout TD Everett DB et al.Impact and effectiveness of 13-valent pneumococcal conjugate vaccine on population incidence of vaccine and non-vaccine serotype invasive pneumococcal disease in Blantyre, Malawi, 2006–18: prospective observational time-series and case-control studies., 5Heinsbroek E Tafatatha T Phiri A et al.Pneumococcal carriage in households in Karonga District, Malawi, before and after introduction of 13-valent pneumococcal conjugate vaccination. they describe a decrease in total incidence of invasive pneumococcal disease before the introduction of PCV13 and a decrease in the incidence of vaccine-serotype invasive pneumococcal disease after introduction of PCV13 among children aged 1–4 years and 5–14 years. This reduction in vaccine-serotype invasive pneumococcal disease was accompanied by an increase in the incidence of non-vaccine-serotype invasive pneumococcal disease.It is apparent that PCV13 immunisation has had an impact on the control of invasive pneumococcal disease even in a setting in which incidence was already falling. The greatest impact was seen in the vaccinated population, in whom it reduces carriage rates.5Heinsbroek E Tafatatha T Phiri A et al.Pneumococcal carriage in households in Karonga District, Malawi, before and after introduction of 13-valent pneumococcal conjugate vaccination. Although there was an increase in non-vaccine serotypes from 4 years after the introduction of PCV13, the total incidence of invasive pneumococcal disease remained low because the magnitude of that increase was relatively small compared with the overall reduction in the disease incidence.However, the indirect effects of the immunisation in infants and older adults were minimal, which is in marked contrast to effects observed in high-income countries, where substantial reductions in the incidence of invasive pneumococcal disease and pneumonia have been shown in unimmunised children and adults.6Centers for Disease Control and Prevention
Direct and indirect effects of routine vaccination of children with 7-valent pneumococcal conjugate vaccine on incidence of invasive pneumococcal disease–United States, 1998–2003. Nevertheless, these modest indirect effects are comparable to those seen after PCV13 vaccination in other sub-Saharan African countries.7Mackenzie GA Hill PC Jeffries DJ et al.Effect of the introduction of pneumococcal conjugate vaccination on invasive pneumococcal disease in The Gambia: a population-based surveillance study., 8Hammitt LL Etyang AO Morpeth SC et al.Effect of ten-valent pneumococcal conjugate vaccine on invasive pneumococcal disease and nasopharyngeal carriage in Kenya: a longitudinal surveillance study. These findings suggest that vaccination of infants with PCV alone might not be sufficient to protect vulnerable populations against invasive pneumococcal disease, highlighting the need for exploration of other interventions to deal with the burden of invasive pneumococcal disease in sub Saharan Africa. The decreasing incidence of invasive pneumococcal disease before introduction of PCV13 vaccination emphasises the need for multiple public health interventions to combat disease burden. Proper management of chronic medical conditions (eg, HIV infection, diabetes, heart disease, and lung disease) should be considered in efforts to decrease the incidence of invasive pneumococcal disease. Improved nutrition, better housing, and reducing indoor air pollution should also be implemented.

Considering both the direct and indirect effects of the vaccines, Bar-Zeev and colleagues' findings provide further evidence to the scientific community and policy makers regarding the use of PCV and its role in reducing the burden of pneumococcal disease in Africa. The persisting burden of disease in infants and adults needs further exploration. Future studies should focus on finding effective vaccine strategies to protect infants, older adults, and other vulnerable groups of people. These future studies should examine the safety and effectiveness of maternal antenatal vaccination with PCV, to reduce the incidence of infant pneumococcal disease in areas where pneumococcal acquisition occurs very early in life, and investigate the direct and indirect effects of PCV booster doses in infants. The emergence of non-vaccine serotype disease should prompt further long-term surveillance to monitor changes and generate additional knowledge for optimisation of future vaccine design.

I declare no competing interests.

References1.O'Brien KL Wolfson LJ Watt JP et al.

Burden of disease caused by Streptococcus pneumoniae in children younger than 5 years: global estimates.

Lancet. 374: 893-9022.Troeger C Forouzanfar M Rao PC et al.

Estimates of the global, regional, and national morbidity, mortality, and aetiologies of lower respiratory tract infections in 195 countries: a systematic analysis for the Global Burden of Disease Study 2015.

Lancet Infect Dis. 17: 1133-11613.Feikin DR Kagucia EW Loo JD et al.

Serotype-specific changes in invasive pneumococcal disease after pneumococcal conjugate vaccine introduction: a pooled analysis of multiple surveillance sites.

PLoS Med. 10e10015174.Bar-Zeev N Swarthout TD Everett DB et al.

Impact and effectiveness of 13-valent pneumococcal conjugate vaccine on population incidence of vaccine and non-vaccine serotype invasive pneumococcal disease in Blantyre, Malawi, 2006–18: prospective observational time-series and case-control studies.

Lancet Glob Health. 9: e989-e9985.Heinsbroek E Tafatatha T Phiri A et al.

Pneumococcal carriage in households in Karonga District, Malawi, before and after introduction of 13-valent pneumococcal conjugate vaccination.

Vaccine. 36: 7369-73766.Centers for Disease Control and Prevention

Direct and indirect effects of routine vaccination of children with 7-valent pneumococcal conjugate vaccine on incidence of invasive pneumococcal disease–United States, 1998–2003.

MMWR Morb Mortal Wkly Rep. 54: 893-8977.Mackenzie GA Hill PC Jeffries DJ et al.

Effect of the introduction of pneumococcal conjugate vaccination on invasive pneumococcal disease in The Gambia: a population-based surveillance study.

Lancet Infect Dis. 16: 703-7118.Hammitt LL Etyang AO Morpeth SC et al.

Effect of ten-valent pneumococcal conjugate vaccine on invasive pneumococcal disease and nasopharyngeal carriage in Kenya: a longitudinal surveillance study.

Lancet. 393: 2146-2154Article InfoPublication HistoryIdentification

DOI: https://doi.org/10.1016/S2214-109X(21)00258-8

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