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[ISLAMABAD] Health researchers say they have identified whooping cough in children who had previously been vaccinated against the potentially life-threatening disease in Pakistan's Sindh province.

Writing in the journal Public Health (23 March) [1], the researchers say their discovery suggests new work is needed to tailor vaccines and immunisation programmes to whooping cough strains unique to Pakistan.

The researchers, from Shah Abdul Latif University in Sindh, and COMSATS Institute of Information Technology in Islamabad, studied 700 children in southeastern Sindh, who — despite having previously been vaccinated — were suspected of being infected with Bordetella pertussis, the bacteria that causes whooping cough.

They took samples from 22 children aged from six months to seven years who had "cough-like" symptoms.

Detailed culture and molecular tests confirmed that the 22 children were infected with the bacterium. The study noted that the infection rate could have been higher as not all 700 children were subject to the same analysis.

The study was unable to identify a specific reason for the re-emergence, but said it could be the result of genetic differences between circulating strains and strains used to make the vaccines, a problem that has been observed elsewhere in the world.

It also found an overwhelming majority of Pakistani health professionals were unaware that vaccinated adults can sometimes be reservoirs of lingering bacteria, which they can pass to childen by coughing.

"Present immunisation practices may not be sufficient in protecting infants and children under five years of age against pertussis," the report concluded.

It also suggested giving children a booster shot at the age of four – a practice common in European countries facing similar challenges with vaccine efficacy.

But officials at Pakistan's National Institute of Health (NIH), which operates under the Ministry of Health, have rejected the findings.

NIH executive director Berjees Mazher Kazi told SciDev.Net that other factors might be reducing the effectiveness of immunisation programmes, including a child's immune status, general hygiene conditions, and poor vaccine transport and storage facilities.

Whooping cough commonly occurs in early infancy and accounts for 300,000 deaths per year, mostly among unvaccinated babies. It remains in circulation round the year.

Outbreaks can be triggered by changing weather conditions, Syed Habib Bukhari, associate professor of biosciences at CIIT, and a co-author of the study, told SciDev.Net, adding that the disease is often not diagnosed, and is therefore widely unreported in Pakistan.

An earlier study by Bukhari's team focused on another strain of the disease, B parapertussis, which was also found in vaccinated children.

That study, published in December 2010 [2], found that the vaccine used in Pakistan protects against B pertussis, but offers less protection against B. parapertussis.

The 2010 study recommended further research to confirm the findings, and notes that this may provide evidence for the introduction of vaccines to protect against all strains found in Pakistan.


[1] Public Health (26 March 2012) DOI:10.1016/j.puhe.2012.02.001
[2] FEMS Immunology & Medical Microbiology, Vol 63, Issue 3 (December 2011) DOI: 10.1111/j.1574-695X.2011.00861.x