This is the short version of the meningococcal vaccine post. For the long version and references, check here.
What are the “meningitis vaccines”?
There are two basic types of meningitis: viral and bacterial. There are no vaccines targeting viral meningitis. There are three vaccines targeting causes of bacterial meningitis: HiB, pneumococcal, and meningococcal. Meningococcal will be discussed here and the others in future Weekly Topics.
What is meningococcus?
Neisseria meningitidis, the meningococcal bacteria, is passed by coughing or contact with saliva and is normally present in the respiratory tracts of healthy people without causing disease. Probably 100% of people become infected at some point and about 5-35% of the population is infected with the bacteria at any time. Asymptomatic carriers carry the bacteria for months or even years.
N. meningitidis is divided into serogroups (not strains). Serogroup B is responsible for 60% of U.S. cases of meningococcal disease and is targeted by one vaccine. Serogroups A, C, Y, and W-135 are less common and are targeted by another vaccine (some countries have a C-only vaccine). Natural infection with one serogroup or with a different species called N. lactamica confers immunity to all serogroups and it’s rare for an unvaccinated individual to become infected with one serogroup and later become infected with a different serogroup.
According to the CDC, “For unknown reasons, incidence has declined since the peak of disease in the late 1990s…. This decline began before implementation of routine use of meningococcal vaccines in adolescents and have occurred in all serogroups.” Last year (2014), there were a total of 386 meningococcal disease cases and an estimated 39-58 deaths.
Meningococcal disease occurs most frequently in those with suppressed immune systems. Risk factors and prevention techniques are in the longer version of this post.
How effective are the vaccines at preventing asymptomatic carriage?
One study suggested that A/C/Y/W-135 vaccination may reduce the length of (but not eliminate) asymptomatic carriage. However, the vaccine against serogroup B does not prevent asymptomatic carriage. Thus, the vaccines should not be relied upon for herd immunity.
How effective are the vaccines at preventing disease?
As discussed above, natural infection with one serogroup or a related species confers immunity against all serogroups. However, the vaccine potentially protects against only the serogroup in the vaccine. It’s said to be 85% effective, but has never been proven to prevent disease, only to induce an antibody response.
As also discussed above, it’s rare for an unvaccinated individual to become infected with one serogroup and later become infected with another serogroup. However, when N. meningitidis infects a vaccinated individual, the bacteria can change its serogroup in a matter of days to one against which the vaccine offered no protection, whereby it causes disease in and kills the vaccinated individual.
How great is the antibody response produced by the vaccine?
As discussed above, the vaccine has never been proven to prevent disease, only to induce an antibody response. However, following three doses, about half of recipients do not develop an appropriate antibody response, and following four doses, 87% do not respond. Furthermore, the antibodies wane in less than 7 months.
In fact, New Zealand saw an increased incidence of meningococcal disease following three doses of the vaccine. After the four-year vaccination campaign, the New Zealand Herald reported on 109 cases of the vaccine-targeted strain in vaccinated people. For 2006-2008, there were 12 meningococcal deaths, all in vaccinated children. There were no meningococcal deaths in unvaccinated children. Furthermore, the meningococcal disease rate was dropping prior to the introduction of the vaccine but increased during the vaccination campaign.
Is the vaccine safe?
The short version is a resounding no. We will assume the previously discussed false statistic of 85% efficacy is true and combine that with the package inserts’ serious adverse event rate of 1% (A/C/Y/W-135) and 2% (B), the CDC’s estimated 0.3% rate of death following adverse events, and Fall 2015’s U.S. college enrollment of 20.2 million students. If all U.S. college students receive only one injection of each meningococcal vaccine in one year, there will be an estimated 606,000 serious adverse events and 1,818 deaths from meningococcal vaccination of all U.S. college students. Compare that to last year’s 386 meningococcal disease cases and estimated 39-58 deaths in all age groups in the U.S.
Are the meningococcal vaccines linked to autoimmune diseases?
Meningococcal serogroup C or A/C/Y/W-135 vaccines have been definitively or tentatively linked to three autoimmune diseases: Henoch-Schönlein purpura, bullous phemigoid, and Guillain-Barré Syndrome. The serogroup B vaccine took so long to develop primarily because its antigens look very similar to structures on human brain cells, which may increase the risk of neurological autoimmune diseases. However, the serogroup B vaccine is too new to know yet whether it increases the risk of autoimmune diseases.
So what’s the bottom line?
The bottom line is that meningococcal bacteria infect probably 100% of the population and exceptionally rarely cause disease. Natural infection with one serogroup confers immunity against all serogroups whereas vaccination provides immunity only against the serogroups targeted by the vaccine and increase one’s risk to serogroups not included in the vaccine. After infecting a vaccinated person, the bacteria can change their serogroup to one against which the vaccinated individual has no protection. Furthermore, in some populations, vaccination was demonstrated to increase the incidence of meningococcal disease and death. The risk of death from the vaccine far outweighs the risk of death from the disease. The vaccine does not prevent asymptomatic carriage, so the vaccine offers no herd immunity effect.