Does whooping cough vaccine for parents protect newborns (and who should pay for it)?

Infants too young to receive the whooping cough vaccine are at greatest risk. flickr/rifqy

Recent news reports say the free whooping cough vaccine for parents to protect newborns will be discontinued because it is not effective. Parents who’ve been told this is an important step to protect their baby are dismayed and confused.

The key message is that whooping cough vaccine given to parents, especially mothers, should provide protection to their newborn. But how much protection is uncertain and depends on vaccine factors and logistics.

Historical background

The initial driver of the decision by most states and territories to make whooping cough vaccine (at various times since 2009) available free of charge to parents of newborns was the urgency of an epidemic coupled with tragic and widely reported infant deaths.

The rationale for vaccinating parents is twofold. First, infants too young to themselves receive at least two doses of whooping cough vaccine are at greatest risk from severe disease – almost all deaths from whooping cough occurring in those under eight weeks old.

Second, studies of how infants acquire whooping cough consistently identify parents, and in the youngest babies especially mothers, as the most common source of infection. As whooping cough vaccine protects adults, it should also reduce transmission to infants.

So far, so good.

It wasn’t long before state and territory governments looked to the Commonwealth to take over funding of pertussis vaccine for parents under the National Immunisation Program (NIP) in lieu of their emergency funding.

Limited options

But the Federal Government has a legislated process for funding vaccines under the National Immunisation Program (NIP) – the Pharmaceutical Benefits Advisory Committee (PBAC) must recommend it as cost-effective. Without the PBAC’s recommendation, the government’s hands are tied.

In the case of whooping cough vaccine for parents of newborns, the PBAC concluded that the costs were high and the benefits uncertain.

In considering costs and benefits, the PBAC is most interested in evidence of benefit from large clinical trials that directly compare active vaccine with no vaccine or a different vaccine. This is then used to estimate how many dollars it takes to save one quality-adjusted life year (QALY), which roughly translates to “how many doses of vaccine would need to be given at the quoted vaccine cost to gain one extra year of full quality life?”

flickr/sanofi pasteur

This is a problem for assessing the potential impact of whooping cough vaccine doses for adults to protect infants (known as “cocooning”). First, although any death from pertussis is tragic, there are, on average, less than three identified each year and even factoring in hospitalisations from pertussis would not add up to many QALYs to gain (compared to, say, drugs to prevent heart attacks in adults).

Second, randomized trials of pertussis vaccine for parents are impractical and even lesser-quality evidence, such as before-after studies evaluating this strategy in the field, were not available at the time of the PBAC review.

Inaccurate reporting

That said, the way statements to a Victorian Parliamentary Committee were widely reported was incorrect. The PBAC did not “determine vaccinating parents was not effective in protecting newborns”. Rather, it found that, under its criteria, this was unlikely to be cost-effective.

Similarly, the PBAC didn’t “determine there is no clinical effectiveness”, it said clinical effectiveness was uncertain. In any case, the role of making clinical recommendations falls to the Australian Technical Advisory Group on Immunisation (ATAGI), a group of vaccine experts responsible for writing the Australian Immunisation Handbook.

Based on the available evidence of the source of infection for infants, ATAGI has recommended vaccinating parents against whooping cough since it was included in its 2003 Handbook. The same recommendation was made by the comparable group in the United States.

To cocoon or not to cocoon

There are currently several on-going studies investigating the impact of the cocooning strategy on severe disease in infants (including one by my centre in collaboration with the NSW Ministry of Health). These studies may show that vaccinating parents fails to protect their newborns – but, if so, this is unlikely to be due to lack of effectiveness of the vaccine.

flickr/sanofi pasteur

A baby who gets whooping cough despite her parent(s) being vaccinated is likely to have acquired the infection from other people, or because her parents were vaccinated too late (as is likely if they wait for a routine visit to a doctor when the baby is six weeks old rather than being vaccinated in the maternity hospital).

This highlights the problem that vaccinating parents doesn’t (and, short of immunizing the whole community, can’t) create a complete “cocoon”. In contrast, direct protection of the newborn can potentially be achieved by only one dose of vaccine to either mother or baby.

Giving the vaccine to the mother in the last months of pregnancy results in high levels of antibodies against whooping cough being transferred to the baby and should protect against the illness from birth. This measure was recommended in the United States in 2011 as preferred to – but not as a replacement of – cocooning.

Giving the whooping cough vaccine to newborns immediately after birth results in earlier acquisition of antibodies against whooping cough and Australia is leading the way in further investigating this in a trial funded by the NHMRC.

We already give hepatitis B vaccine at birth in Australia, and coupling it with whooping cough vaccine at birth, if confirmed to significantly hasten protection, could also be valuable. We know that not all women will be vaccinated during pregnancy, even if this is recommended.

Like cocooning, there is currently no concrete evidence that either a dose of whooping cough vaccine to pregnant mothers or to the baby immediately after birth prevents death or severe disease, which (in the context of the issues discussed above) may make it challenging even for these one-dose, more direct approaches to get below the PBAC limbo stick.

What’s certain is that whooping cough will not go away and, tragically, deaths in very young babies will still occur without better ways to protect them before they themselves can be protected by immunization.

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