Measles are continuing to spread in Canterbury, with a Christchurch police prosecutor among the latest to reportedly contract the virus.
With 25 confirmed cases of measles in the region since the start of the year, people are being urged to check their vaccination history, and if-in-doubt, revaccinate.
The SMC asked an expert to lay out some facts about the virus and how to know if you’re at risk.
Professor David Hayman, Infectious Disease Ecology and Director, Infectious Disease Research Centre, Massey University, comments:
Who is likely to need a booster?
“Anyone who has only had one measles-containing vaccine (MCV) dose needs a booster. Any adult who has had measles itself or had two doses of measles-containing vaccine (MCV) is considered immune and does not need to be immunised, except in rare circumstances. If people are uncertain if they had two vaccine doses or the disease they should contact their GP.
“Adults who had one vaccine dose are much less at risk than those who have never had any vaccines, but they are more at risk that people that have had two doses. It took some time for health researchers to discover this, so countries like New Zealand that were early to introduce the vaccines are more likely to have cohorts of older people that are not completely protected. For context, in our study of New Zealand cases from 2007 to 2014 we found approximately 83% (955 of 1154 cases) were unvaccinated and fewer than 13% cases (145 of 1154) had one vaccine.
“A second dose to complete the immunisation process is the safest way to increase the protection for that person as well as the New Zealand population.”
How strong is the measles virus?
“Measles is one of the most infectious viruses on earth, and possibly the most contagious among people. The virus is spread through aerosols. Once outside of people the virus, an RNA virus, is not that stable, but it may still last for a couple of hours and that is long enough to infect people without direct contact.
“Another huge problem, however, is that a large proportion of people become infectious and spread the virus before they develop signs, so they present a risk to others without them or their caregivers knowing it.”
Are certain people or communities more at risk?
“The major risk factor for measles is being unvaccinated if people haven’t had the disease. This means that typically children are most at risk. Risk lowers substantially with one dose of measles containing vaccine and further still with two.
“In previous studies, we have found communities who had greater case numbers or have had higher per person risk rates, but these findings are likely confounded by where the virus was introduced now that endemic measles has been nationally eliminated in New Zealand, because the virus will circulate among the susceptible in those communities.”
Conflict of interest statement: David received funding to study measles in New Zealand from the Ministry of Health in 2014.