World health organization regional office for the western pacific regional guidelines

Options for adding rubella vaccine

Once a decision is made to add rubella vaccine the following issues need consideration:

1. 
   The type of introductory campaign
   
2. 
   The timing of the first dose
   
3. 
   The timing of the second dose
   
4. 
   Any need for additional measures to protect pregnant women
   

Introductory campaign

The introductory campaign may be delivered as a one-off event, or can be delivered as part of routine immunization services over a longer period of time. The best approach to implementation will depend on the local circumstances, as well as previous experience with mass campaigns.

The age range for the campaign requires determination of age profile of susceptibility. If that is not available, then the target age should be those aged 1 to 9 years, at a minimum.

Unlike with measles pre-immunization, many adults remain susceptible to rubella – the percentage varies in different settings but is generally between 10 and 25%.¹² As the aim is to ensure that the entire population has over 95% immunity, and this may require extending the campaign to older age groups. However, as it will be harder to reach those who have left school, and because of the additional costs, careful consideration of the benefits and costs of extending the age range will be needed. If high coverage can be achieved, the upper age should be to as high an age group (with inadequate immunity) as is affordable.

Another option may be to target young adults who are in institutions such as the military, training colleges, and large workplaces where there is a lot of mixing of adults. These groups are more likely to spread infection, and are relatively easy to reach through that institution.

Timing of first dose

The change from measles to MR provides a good opportunity to change the timing of the first dose from age nine to 12 months – provided that measles is already under good control. If measles is still common, that means that it may be premature to introduce rubella. However, a successful introductory campaign with MR should improve measles control.

MR can be scheduled at age nine months, if there are other reasons for this scheduling.

Second dose

A second dose of measles vaccine is necessary for measles elimination. It is not necessary for rubella elimination. Therefore, the decision about the second dose will need to balance the extra cost versus the operational simplicity of using only MR rather than two vaccines. For countries that have not yet introduced a scheduled second dose of measles, but deliver the second dose through regular campaigns there would be a preference for using MR as the campaign vaccine and measles for the scheduled dose. [Assumption: second dose is given as campaign because higher coverage is achieved, therefore best to give rubella through the higher coverage option].

Pregnant women

The introductory campaign would ideally include all people at school. This will protect the next generation of pregnant women directly, as well as indirectly protect all pregnant women by reducing the spread of rubella virus.

However, depending on the proportion of adults who remain susceptible, there will still be a risk of rubella outbreaks affecting adults. Should additional measures be undertaken to protect these women?

In industrialized countries, women are screened antenatally, and those without rubella immunity are immunized post-partum. As the blood test is more expensive than MR vaccine, resource-poor countries could simply immunize (unvaccinated) women post-partum without any screening. However, this would be an adjunct to rubella control, and only becomes necessary if sufficient population immunity has not been achieved.

Rubella vaccine is contraindicated in pregnancy because of the theoretical risk of CRS from the vaccine virus. But, there is no evidence of CRS from vaccine, so if a pregnant woman is accidentally given MR, there is no need to consider termination of the pregnancy, but the outcome should eb monitored.

Outbreak response

A rubella outbreak leads to urgent consideration of rubella vaccine. Early recognition (and hence timely response) requires laboratory testing to be in place. As countries implement intensified measles surveillance and incorporate rubella surveillance as part of that system, so countries will need to plan how they will respond when a rubella outbreak is identified.

To control an outbreak through immunization requires a very rapid response as well as epidemiological assessment of the outbreak. Preparing a plan for investigation and emergency response with a wide-age range campaign can then be useful for other public health emergencies. Unless such plans are already in place, it is unlikely that there will be adequate assessment of the need for a campaign, nor that it could be implemented rapidly enough to stop the outbreak.

Even if a plan is in place, there will be considerable challenges to achieving a response that is timely enough to prevent the outbreak. At present, there is no evidence of an outbreak being curtailed by immunization, and hence the need to implement an immunization campaign before an outbreak occurs.

Rubella immunization must not be introduced unless very high levels of coverage can be achieved and maintained indefinitely (to prevent a potential increase in CRS cases as discussed above). The requirement for very high coverage also applies to the initial campaign.

All countries should develop plans on implementing a wide-age range immunization campaign for preparedness to a wide range of potential emerging diseases, including rubella.

Assessing disease burden during a rubella outbreak

A detailed epidemiological assessment of an outbreak provides useful information about the age-susceptibility profile of the population, and hence the risk of CRS. As with any outbreak, the first step is to confirm the diagnosis with laboratory tests on at least 5 to 10 of the cases, using standard case definitions.

Experience in Tonga and Samoa has shown that it is also important to assess the incidence of any complications, especially rubella encephalitis to get the total picture of disease burden.

As rubella tends to be an epidemic disease with long gaps between outbreaks (particularly in island or isolated populations), it may be useful to search for evidence of previous outbreaks to assess how frequent any future outbreaks are likely to be.

Age distribution

The age-distribution of cases will show the overall pattern of immunity by age, and hence give an indication of adult susceptibility. The age distribution can also provide some evidence of previous outbreaks as well as provide guidance on the upper age to be targeted by immunization. Data from health clinics and hospitals need to be collated and analysed, using standard case definitions (Annex 4).

Counting cases presenting to health clinics can lead to a significant ascertainment bias, as parents are more likely to seek advice for young children while older children and adults may not present if the disease is mild.

The attack rate can also be used to give an indication at the stage of the epidemic cycle at the time of the survey and inform the urgency and requirement for any intervention. The highest attack rates are usually in 5 to 9 year-olds. As about half the cases can be asymptomatic, as the attack rate in this group approaches about 30% epidemic is likely to have peaked.

A community survey in one or more representative villages or communities should be undertaken, using a simple clinical case definition such as recent acute rash and fever illness, to estimate the attack rate in all age groups

Risk to pregnant women

The risk to pregnant women can also be measured more directly by undertaking serosurvey. To be most useful, the survey needs to be early in the outbreak so as to get a better assessment of immunity before the outbreak peaks. Ideally, a random sample of all pregnant women would be tested, but a convenience sample of women attending for an antenatal clinic is likely to provide adequate results in most cases. However, these women may not be representative of all pregnant women in some countries, and if so a more widely based random survey should be undertaken.

In general a serosurvey of about 100 women will provide sufficient reliable information on susceptibility.

A serosurvey of pregnant women provides an estimate of the potential CRS burden – this is best undertaken before rather than during an outbreak

The exposure history of pregnant women to cases of fever and rash, as well as their own experience of illness should be routinely collected at antenatal visits during a rubella outbreak to enable identification of potential CRS cases for screening and follow-up of their babies. Procedures need to be established and disseminated for follow-up of pregnant women who are suspected or known to have been exposed to rubella infection.

Women attending for antenatal care during the outbreak who have been exposed to, or suffered, an illness with fever and rash need to have their babies followed-up for CRS

Incidence of complications

Although it is usually a mild disease in children and adults, there may be an increased rate of complications in certain populations. The recent finding of high rates of encephalitis in the Tonga and Samoa outbreaks emphasise the need to monitor and evaluate any complications. These can be monitored primarily in hospital-based cases.

All rubella complications, especially rubella encephalitis, should be monitored and evaluated.