When a cough gets nasty

It is critical that the current whooping cough epidemic should not undermine public trust in vaccination programs, write Jodie McVernon and Julie Leask.

Even though we have had a whooping cough (pertussis) vaccine since the 1950s, the disease is proving difficult to control and beat. Dealing with its resurgence requires clear communication about the importance of vaccination as well as research to understand why we can’t beat this elusive bug once and for all.

Whooping cough has killed seven infants in Australia since 2008 and left many more needing hospital care. But efforts to understand the illness must recognise the myriad reasons for the current outbreak.

Vaccine refusal is one part of the cause, but more testing as well as better tests for the disease, the short period of protection, and waning adult immunity are all contributing to whooping cough’s resurgence. Others are proposing that changes in the bug itself may be at least partly to blame.

The epidemic we are in now (2009-2012) is part of a recurring pattern typical of whooping cough, with large outbreaks roughly every three to five years.

But it’s also unique. Compared with epidemics in 1997 and 2002, many more infections have been reported even though there are fewer deaths and roughly the same number of hospitalisations.

The number of cases has only recently started to fall so the public is right to ask why there’s so much whooping cough around despite vaccinations.

Much of the blame has been levelled at vaccine refusers. And vaccine refusal, as well as the tendency for refusers to geographically cluster, certainly promotes the spread of infections. But Australia has maintained high vaccination rates over recent years, with 94 per cent of two-year-olds completely up to date with their vaccines. And it’s not just communities with high rates of refusal that are affected by whooping cough.

In fact, most people who get this disease have had at least one dose of the pertussis vaccine.

The rise in detection of cases is partly because doctors are getting much better at recognising mild symptoms and we have more sensitive tests to diagnose the infection. This means people who previously may have been thought to have a viral cough or cold are now being diagnosed with whooping cough.

Whooping cough, like many other infectious diseases, usually becomes less severe as we grow older. Very young babies, too young to be vaccinated, are at greatest risk of hospitalisation and death.

To try to reduce this risk, authorities have promoted vaccination of groups who are likely to pass the disease on to babies, including parents, grandparents, childcare workers and healthcare professionals.

Local and international efforts are helping us to understand how to better use vaccines to control this troublesome infection. A current national research project funded by the government, for instance, is testing whether giving newborns whooping cough vaccine is safe and will protect them sooner.

Another project is exploring how well newborns are protected if their mothers are vaccinated against pertussis in the second half of pregnancy, a strategy recently recommended by the US Advisory Committee on Immunisation Practices.

Opponents of vaccine programs could argue the ongoing problem with whooping cough despite mass vaccination programs means we shouldn’t bother with the shots. They suggest it’s better to get natural immunity and avoid what they believe is a risky vaccine.

In reality, the whooping cough vaccine is overwhelmingly safe and the unvaccinated are at risk of more severe disease even well beyond infancy. And when they do get whooping cough, they’re likely to have more bugs and spread it more efficiently.

As recently as the 1940s, hundreds of people were dying from whooping cough every year, in a population only a third of the present size. The introduction of whooping cough vaccines in the 1950s changed all that and the vaccine’s contribution to saving lives must be recognised.

Our vigilance in pursuing this bug stems from the belief that even one death that could have been prevented with a vaccine is too many. But, we must acknowledge the limitations of vaccine programs and this acknowledgement gives rise to a genuine concern that public confidence in vaccine programs could be undermined or that opponents of vaccinations will amplify such a message or decontextualise it.

This fact shouldn’t discourage clear and rational appraisal of immunisation programs to further enhance their existing achievements in disease prevention.

Associate Professor Jodie McVernon is principal research fellow at the Melbourne School of Population Health at the University of Melbourne. Dr Julie Leask has a background in nursing and midwifery and is now a postdoctoral research fellow at the school of public health, University of Sydney. A version of this article first appeared on The Conversation online.

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