Varicella vaccination for healthcare workers

In December 2003, the Oka vaccine to prevent chickenpox (varicella) was licensed in the United Kingdom for use in susceptible healthcare workers.¹ One year later a survey of consultant virologists, who are members of the Clinical Virology Network and who between them provide virology services for 38 trusts located around the United Kingdom, suggests that fewer than half of the trusts have implemented the policy (J Breuer, personal communication, 2004). Lack of funds or problems within occupational health departments are perceived as the main obstacles. Failure to protect healthcare workers against this potentially serious infection has health and safety implications both for themselves and the patients they care for.

The initiative was designed to achieve two main objectives. The aim was, firstly, to reduce the risk of exposure of vulnerable patients to staff with varicella, and, secondly, to reduce the high costs incurred after an exposure to varicella zoster virus. Brief mention was also made of the protection that would be afforded to healthcare workers themselves. No funding was attached to this initiative but the UK health departments said that, on the basis of health economic studies,² the policy would be overall cost neutral and may be cost saving to trusts.¹

Little information is available from primary care organisations, for which funding for varicella vaccination of healthcare workers in a new occupational health budget has been provided. However, anecdotal evidence indicates that here too implementation of the initiative has been patchy.

Even where vaccine programmes are implemented, uptake among healthcare workers may be low, as is the case for influenza vaccination, where acceptance rates are as low as 15%.³ Worries about side effects, suspicions about vaccines, and a general perception that the natural infection is mild, all contribute to staff ambivalence towards these optional programmes.³ For many microbiology, virology, occupational health, and infection control departments the workload associated with preventing hospital acquired varicella outbreaks remains as high as ever.

The primary purpose of the varicella immunisation programme for healthcare workers is to protect seronegative patients. Chickenpox in immunosuppressed people, pregnant women, and infants born to seronegative mothers may lead to life threatening pneumonitis and other complications in 10-30% and is fatal in 15-25 patients every year.⁴ Maternal varicella in the first 20 weeks carries a 1-2% risk of congenital varicella syndrome for the fetus.⁴ Consequently, hospitals currently make strenuous efforts to prevent nosocomial spread of varicella zoster virus from infected staff and patients to these vulnerable patients. This includes the administration of specific varicella zoster immunoglobulin and the quarantining of potentially infectious staff and patients.⁵

Although 95% of adult patients born in the United Kingdom and staff are immune to chickenpox, only 75-85% of adults who have grown up in tropical countries such as the Philippines, the Indian subcontinent, and the West Indies are immune. Hospitals with high numbers of staff or patients from these area are at greater risk of nosocomial outbreaks.⁶ The close proximity of infected cases (children with chickenpox and adults with zoster) to susceptible patients and staff within the hospital provides an ideal environment for viral transmission to occur.⁷

So are there benefits to staff from vaccination against varicella, or is it a completely altruistic action? Almost without exception, seronegative adults acquire chickenpox naturally over time, either from household contact or, in the case of healthcare workers, occasionally from occupational exposure.⁷ Chickenpox in healthy adults is a severe disease. Complications, including pneumonitis and encephalitis, are over 100 times more common than in children, and mortality is at least 20 times higher.⁷ By contrast the Oka vaccine is very safe for adults. Vaccine rashes occur in 5-10% of adults compared with over 90% of adults with wild type chickenpox.⁸ Vaccine rashes are mild with on average fewer than 60 lesions, contrasting with over 300 lesions characteristically seen in wild type disease.⁹ Transmission of Oka vaccine virus to susceptible household contacts has been documented in three cases in16 million doses of vaccine administered, whereas wild type virus infects 70-90%.⁸,¹⁰ Reactivation of Oka vaccine strain is estimated to occur five to seven times less commonly than the naturally occurring virus.¹⁰ Vaccine related deaths in adults and children have not been recorded in 40 million doses administered in the United States⁸ compared with a mortality of one in 4000-10 000 in adults infected with wild type chickenpox.¹¹ Serious complications have been reported to occur in one in 10 000 people receiving the vaccine compared with one in 400 patients with chickenpox. Inadvertent immunisation of 362 pregnant women has resulted in no congenital infections or abnormalities.⁸

Considerable doubts exist in the United Kingdom about the use of varicella vaccine to reduce transmission of varicella in children. Most particularly, data from models predict that such a strategy would result in an increase in zoster among naturally infected adults with adverse health and economic consequences.¹¹ Such reservations would not apply to a school leaver immunisation programme,¹¹ nor do they apply to the current targeted immunisation of healthcare workers. Nosocomial varicella and its prevention by conventional methods have been estimated to cost the NHS in excess of £5m-10m ($10m-20m; €7m-14m) per year.⁵ Included in this figure is the cost of precious nursing and medical time for infection control, which could be better targeted at controlling serious hospital acquired infections such as MRSA. Varicella vaccination is safer for adults than natural chickenpox, is available, and its use in healthcare workers is predicted to be cost saving for trusts.⁵

Hospitals have a duty of care to staff and patients and failure to implement guidelines from the Department of Health on vaccinating against varicella may expose them to medicolegal challenge. At the same time, more information needs to be made available to staff about the benefits to them of varicella vaccination and active efforts made to encourage uptake.