Family doctors are being urged to clear waiting lists for child immunisation clinics following an upsurge in cases of whooping cough.
There were 2,466 cases of the potentially deadly infection recorded in the first six months of the year, more than in the whole of last year, according to the Health Protection Agency. And experts believe delays in immunising children could put them at risk.
This year's outbreak is the worst since the early 1990s, and the number of cases is already five times higher than the last surge in 2008.
Whooping cough outbreaks occur around once every three to four years. There have been five deaths so far in 2012 compared to four in 2008. Young babies are at greatest risk.
The Department of Health's Joint Committee of Vaccination and Immunization said it was important children received vaccinations at the right time.
The jab, which also protects against diphtheria, tetanus, polio and Hib meningitis, is offered to babies at two, three and four months old.
The committee is also reviewing options including introducing a booster dose for teenagers.