Guidance

Mumps: risk in pregnancy, infection in healthcare settings and MMR vaccine

Published 28 May 2008

1. Risks of mumps in pregnancy

While it is possible for any virus to have an adverse effect on pregnancy, the evidence base for an increased risk of fetal loss due to mumps in pregnancy is weak and limited to one study dating back to the 1960s. This indicated that there may be an increased risk of fetal loss in the first trimester of pregnancy. There is no evidence of an increased risk of severe congenital abnormality.

There is a possible association between mumps infection and a heart condition, endocardial fibroelastosis. Peri-natal infection may also be associated with respiratory distress around the time of birth and with thrombocytopenia according to case reports.

1.1 Avoiding school settings during a mumps outbreak

There are currently no recommendations for excluding women from such settings for the following reasons:

• if mumps outbreaks are ongoing in the community then excluding women from a setting such as a school or university may not reduce her risk of contracting mumps

• most pregnant women will be immune to mumps

• the evidence that mumps causes problems in pregnancy is weak, and the evidence that exclusion of women is an effective intervention is also weak

There may be specific circumstances that make the risk to a pregnancy of contracting mumps higher for particular individuals.

1.2 Pregnant women who have a known contact with a case of mumps

There are currently no recommended interventions. There is no evidence, that we are aware of, to support the use of human normal immunoglobulin for contacts of cases as this has not been shown to have any benefit.

1.3 Pregnant women developing mumps

There is no evidence we are aware of that pregnant women are at any higher risk of complications of mumps than other adults and no specific treatment other than supportive is recommended.

The evidence base for an increased risk of fetal loss due to mumps in pregnancy is weak. There are no available interventions to reduce any possible risk to the fetus.

1.4 The risks of pregnant women inadvertently having MMR vaccine

Generally, live virus vaccines are contraindicated for pregnant women because of the theoretical risk of transmission of the vaccine virus to the fetus. MMR is not recommended in pregnancy and pregnancy should be avoided for 1 month after vaccination. However rubella vaccine and MMR vaccine have been given inadvertently to pregnant women with no ill effects observed. In particular there has never been a case of congenital rubella syndrome associated with a rubella vaccine virus.

In the UK 123 births were reported to the National Congenital Rubella Surveillance Programme (NCRSP) between 1980 to 1985 in which the mother had received rubella vaccine during the pregnancy and no congenital abnormalities were identified which could have been caused by the vaccine. Other countries have carried out similar evaluations of the impact of rubella vaccine and found no increased risk to children.

If a pregnant woman receives MMR or if she becomes pregnant within 4 weeks after vaccination then she should be informed about the theoretical risk to the fetus and the risk put in context (outlined above). It is not an indication to terminate the pregnancy.

The Immunisation department of UK Health Security Agency carries out surveillance of women given certain vaccines in pregnancy (VIP). This surveillance was established in 1981 specifically for rubella vaccine, originally under the National Congenital Rubella Surveillance Programme. The VIP surveillance currently covers inadvertent administration of varicella, HPV and MMR vaccines. More information for health professionals, including the form for reporting cases is available.

Similarly there is no reason to test women before vaccinating or to exclude women from vaccination who might be in the early peri-conceptual period but who have not missed a period.

Standard practice can be followed in immunising schoolgirls who are old enough to be pregnant.

1.5 The risks to pregnant women in contact with people who received MMR

Person-to-person transmission of both mumps and measles vaccine viruses has never been documented. Rubella vaccine virus has been found in body fluids such as breast milk. Adult to adult transmission of rubella vaccine virus is unknown.

1.6 The risks of mumps to immunocompromised individuals

There are limited data on the outcome of mumps in immunocompromised patients. In one published series of infection in acute lymphoblastic leukaemia patients infection often remained subclinical and similar to that of healthy children.

2. Recommended infection control procedures for cases of mumps in a healthcare settings

Nosocomial spread of viruses can occur concurrently with outbreaks in the community. Control of spread of mumps infection is difficult for several reasons:

• the prodromal stage of infection
• the infectiveness of the virus
• a relatively large proportion of asymptomatic cases (about 30%)

Therefore, transmission to other susceptible individuals is likely to have occurred before cases are diagnosed. There are only 3 recent reports of nosocomial transmission of mumps in the published literature. In all 3, none of the control measures instituted appeared to be highly effective in preventing onward transmission.

Such incidents can be disruptive to staffing, may lead to prolonged in-patient stays, and can cause morbidity in both staff and patients. There is no evidence to suggest that individuals who are immunocompromised are at increased risk of the complications of mumps. Indeed, the only case series in leukaemic patients suggests that mumps may follow a milder course in such groups.

Clearly the best way to prevent such incidents is by maintaining high vaccine uptake in the community. The risk of staff members introducing mumps or being affected during an outbreak can also be reduced by screening (either by history or by antibody testing) and vaccination on recruitment. Most older health care workers (born before 1980) are likely to be naturally immune to mumps, but may require MMR vaccine to ensure that they are covered for measles and rubella. Those born after 1980 are at higher risk of being susceptible and should be offered MMR if they have not already had 2 doses.

Once cases have been diagnosed in the hospital, vaccination of susceptible contacts (including all staff born after 1980 who do not have documentation or 2 dose of MMR) should be recommended. Although this will not prevent infection in those already exposed it may, however, prevent second and third waves of infection in that setting It will also ensure that they are fully protected for measles and rubella.

The index case should be isolated and respiratory precautions (gown and gloves) should be used for patient contact. Negative pressure rooms are not required. Isolation should last 5 days after the beginning of illness, during which time shedding of virus is likely to occur.

Cohort isolation should be considered for secondary cases and contacts of cases who may develop the disease. During a large community outbreak, new admissions may also need to be considered for cohort isolation.

Hospital staff with clinical mumps infection should be excluded from work for 5 days from the onset of illness.

Hospital staff who have been in contact with a case of mumps should be allowed to continue work in most instances. Most of those born before 1980 will be immune and screening for mumps IgG is likely to identify many false negatives. Those born after this date who do not have 2 documented doses of MMR should be assumed to be susceptible. All staff should be given information on mumps and advised that, should they become febrile or have any non-specific symptoms of viral infection, they should visit occupational health before entering the ward. At this stage a risk assessment can be made, and those working in high risk settings, may be deferred or deployed in other settings.

2.1 Routine policy for vaccination of healthcare workers

Protection of healthcare workers is especially important in the context of their ability to transmit measles or rubella infections to vulnerable groups. Whilst they may need MMR vaccination for their own benefit, they also need to be shown to be immune to measles and rubella for the protection of their patients.

Satisfactory evidence of protection would include documentation of:

• having received 2 doses of MMR or
• positive antibody tests for measles and rubella

Mumps is of less concern than measles and rubella, but the mumps outbreaks are an opportunity to check MMR status. A history of mumps is not that helpful in deciding whether to vaccinate. For reasons of practicability, it is sensible to focus on vaccinating the highest susceptibility group, which is adults born since 1980. Once vaccinated, healthcare workers can work as normal.

3. Using MMR for post-exposure prophylaxis

Antibody response to the mumps component of MMR vaccine does not develop soon enough to provide effective prophylaxis after exposure to suspected mumps. Even where it is too late to provide effective post-exposure prophylaxis with MMR, the vaccine can provide protection against future exposure to all 3 infections. Therefore, contact with suspected measles, mumps or rubella, provides a good opportunity to offer MMR vaccine to previously unvaccinated individuals.

If the individual is already incubating measles, mumps or rubella, MMR vaccination will not exacerbate the symptoms. In these circumstances individuals should be advised that a mumps-like illness occurring shortly after vaccination is likely to be due to natural infection. If there is doubt about an individual’s vaccination status, MMR should still be given as there are no ill effects from vaccinating those who are already immune.

3.1 Should protection of contacts be provided with immunoglobulin?

Human normal immunoglobulin (HNIG) is not routinely used for post-exposure protection from mumps since there is no evidence that it is effective.

4. Who can have the MMR vaccine

MMR vaccine can be given to individuals of any age. Entry into college, university or other centres for further education, prison or military service provides an opportunity to check the immunisation history. Those who have not received MMR vaccine should be offered MMR immunisation.

The decision on when to vaccinate adults needs to take into consideration the past vaccination history, the likelihood of an individual remaining susceptible and the future risk of exposure and disease:

• individuals who were born between 1980 and 1990 may not be protected against mumps but are likely to be vaccinated against measles and rubella. They may have never received a mumps-containing vaccine or had only 1 dose of MMR and have had limited opportunity for exposure to natural mumps. They should be recalled and given MMR vaccine. If this is their first dose, a further dose of MMR should be given from one month later

• individuals born between 1970 to 1979 may have been vaccinated against measles (and rubella if female) and many will have been exposed to measles, mumps and rubella during childhood. However, this age group should be offered MMR wherever feasible, particularly if they are considered to be at high risk of exposure. Where such adults are being vaccinated because they have been demonstrated to be susceptible to at least one of the vaccine components, then either 2 doses should be given, or there should be evidence of sero-conversion to the relevant antigen

• individuals born before 1970 are likely to have had all 3 natural infections and are less likely to be susceptible. MMR vaccine should be offered to such individuals on request, or if they are considered to be at high risk of exposure. Where such adults are being vaccinated because they have been demonstrated to be susceptible to at least one of the vaccine components, then either 2 doses should be given, or there should be evidence of sero-conversion to the relevant antigen

It is probably not acceptable to refuse vaccination to someone on the grounds of being above a certain age as one cannot be absolutely sure that someone is not one of the tiny minority that are susceptible above this age. However, if patients are told that they are probably immune, most are fairly sensible and would not then request MMR.

4.1 Age cut off for MMR vaccine

From a population perspective those born before 1980 will more than likely be immune due to exposure to natural mumps virus. However if an individual requests MMR despite this reassurance then it should be given.

4.2 The number of MMR vaccinations an individual can receive

There is no limit to the number of MMR vaccinations an individual can receive. The risk of adverse reactions falls with increasing number of doses of MMR (unlike inactivated vaccines such as tetanus) so the benefit of ensuring protection outweighs any risk of an additional dose of MMR.

If an individual cannot recall whether:

• they have received MMR (or whether this was MR or single vaccines)

• the exact number of vaccinations

Then they should receive additional MMR up to a total of two documented vaccinations, at least 1 month apart.