PERTUSSIS, or whooping cough, is a highly contagious respiratory disease caused by the bacterium Bordetella pertussis. The disease can affect people of any age, but can lead to severe coughing spells, complications, and even death in infants below 12 months.

Under the Malaysian National Immunisation Schedule, every child is protected against this disease through routine DTP (diphtheria-tetanus-pertussis) vaccinations given at two, three, and five months. Unless your child has completed the vaccination course, he remains vulnerable to pertussis. An additional shot, or booster dose, is administered at 18 months to reinforce your child’s immunity.

How long does the protection last?

The immunity from childhood pertussis vaccination does not last forever. The effectiveness of the vaccination typically fades over four to 12 years. Your child’s immunity against pertussis would have decreased by the time he reaches 12 years old.

According to the US Centers for Disease Control and Prevention (CDC), in 2004, there were 25,000 cases of pertussis in the US. Out of these, more than 8,000 were among adolescents and more than 7,000 among adults. This indicates that adolescents and adults remain at risk of pertussis infection despite being immunised during childhood.

The number of cases of pertussis reported in Malaysia (as stated by the World Health Organisation) from 1980 until 2009 have been erratic. The highest number of cases was reported in 1985. Over the last five years, there have been between five and 15 cases reported each year (see table).

Transmission from adolescents and adults

Unlike in infants, pertussis is usually mild and rarely fatal in adolescents and adults.

However, those who are infected are capable of transmitting the disease to unprotected babies and young children. In fact, new parents are often the source of infection in about 50% of pertussis cases in infants.

Pertussis is highly contagious and spreads as airborne droplets. When an infected person coughs or sneezes without covering with a tissue paper or handkerchief, the tiny droplets of water containing the bacteria are released into the air. It spreads when the droplets are inhaled by a nearby person.

The bacteria can also be spread if the water droplet is in contact with the skin of a healthy individual. When the infected person covers his sneeze or cough with his hand and does not wash his hands after that, the object that he touches will then transmit the infection.

The bacteria are then picked up by another person who touches the objects and may touch his nose or mouth, transferring the bacteria.

That is why periodic booster doses are needed for adolescents and adults, not only to keep themselves protected from the infection, but also to build a protective shield around unprotected babies and younger children – known as the cocooning effect – to prevent them from being exposed to the bacteria.

Types of pertussis booster vaccine

For infants and children (below 11 years old)
DTP, available in two forms
· DTwP is the whole-cell vaccine (which has more antigens) that will cause more reaction, such as fever and/or redness at the injection site.
· DTaP is the acellular vaccine, containing only three to five antigens and causes less reaction and fever, but costs more. 

For adolescents and adults (11-64 years old)
· Tdap (tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine) has lower antigens of diphtheria and pertussis, but are just enough to boost the immunity against pertussis. It’s a better substitute compared to Td (tetanus diphtheria) as it does not cover pertussis when one has an injury. Recommended to be taken every 10 years.

The Malaysian Ministry of Health has replaced all whole-cell pertussis vaccines with acellular ones from 2009. There should not be any more DTwP in the whole country by 2010.

Booster vaccination recommendation

The CDC and Advisory Committee on Immunisation Practices currently recommends pertussis booster vaccination in the following groups of people:

· Children at ages of four to six years. Children at this age are recommended to receive the fifth dose (or the booster dose) of the DTaP vaccine.
· Adolescents aged 11 through to 18 years. Adolescents should get one booster dose of Tdap (where the diphtheria and pertussis dose is reduced). This dose is recommended for adolescents who have taken the DTaP shots as children but have yet to receive a dose of Td (tetanus diphtheria). However, for those who have received the Td shot, they are encouraged to get a dose of Tdap as well, as protection against pertussis.
· Adults aged 19 through to 64 years. They should substitute Tdap for one booster dose of Td. Adults who are expected to come into close contact with babies younger than 12 months should get a dose of Tdap to avoid catching and passing the disease to the babies. These include new parents, grandparents, maids, and childcare providers. Healthcare workers who come in direct contact with patients in clinics and hospitals should also get a dose of Tdap.

Furthermore, to reduce the risk of contracting the disease while abroad, travellers should receive this vaccination. This is especially important when travelling in large crowds, such as when Muslims go on pilgrimage. Pertussis is still at large in many parts of the world, hence a little more precaution to avoid the disease while travelling and bringing it home is important.

Side effects of booster vaccinations

With any vaccination, parents are often concerned about any side effects that may result from the vaccine. Children and adults alike who received the DTaP vaccination may have local reactions, which include tenderness, pain, redness, or swelling.

Mild fever, headache, tiredness and nausea may also occur for the adolescents and adults receiving Tdap. However, these are mild, and may or may not interfere with daily activities, but does not require medical attention.

Other severe reactions such as extensive swelling of the arm where the injection was given is quite rare, making up approximately three out of 100 doses. If any unusual condition were to occur – high fever above 38.9 ºC, difficulty in breathing, wheezing, or dizziness – seek the attention of a doctor immediately. Do enquire from your doctor for more advice and information on pertussis booster.

This article is courtesy of the Malaysian Paediatric Association’s Positive Parenting Childhood Immunisation Campaign that is supported by an educational grant from GlaxoSmithKline. The opinions expressed in the article are the view of the author. For further information, please visit www.mypositiveparenting.org.