Measles outbreak in Gothenburg urban area, Sweden, 2017 to 2018: low viral load in breakthrough infections

Abstract

In an outbreak of measles in Gothenburg, Sweden, breakthrough infections (i.e. infections in individuals with a history of vaccination) were common. The objective of this study was to compare measles RNA levels between naïve (i.e. primary) and breakthrough infections. We also propose a fast provisional classification of breakthrough infections. Medical records were reviewed and real-time PCR-positive samples genotyped. Cases were classified as naïve, breakthrough or vaccine infections. We compared clinical symptoms and measles RNA cycle threshold (Ct) values between breakthrough and naïve infections. Sixteen of 28 confirmed cases of measles in this outbreak were breakthrough infections. A fast provisional classification, based on previous history of measles vaccination and detectable levels of measles IgG in acute serum, correctly identified 14 of the 16 breakthrough infections, confirmed by IgG avidity testing. Measles viral load was significantly lower in nasopharyngeal samples from individuals with breakthrough compared with naïve infections (median Ct-values: 32 and 19, respectively, p < 0.0001). No onward transmission from breakthrough infections was identified. Our results indicate that a high risk of onward transmission is limited to naïve infections. We propose a fast provisional classification of breakthrough measles that can guide contact tracing in outbreak settings.

A measles outbreak in Kansai International Airport, Japan, 2016: Analysis of the quantitative difference and infectivity of measles virus between patients who are immunologically naive versus those with secondary vaccine failure

“…In this study, an outbreak of measles reported at the Kansai International Airport in 2016 was investigated using quantitative real‐time polymerase chain reaction (PCR) and virus isolation. Because approximately 50% of patients with measles in this outbreak had vaccination records and showed modified clinical signs, it was considered a typical outbreak even after elimination of measles 13–15 . This study aimed to determine the quantity of viral load based on quantitative real‐time PCR and isolate the virus from clinical specimens to compare the virological features between patients with an immunologically naive status versus those with SVF.…”

Authors’ response: Measles outbreak in Gothenburg urban area, Sweden, 2017/18: lower viral load in breakthrough infections

“…We agree, as stated in our paper, that there are reports of onward transmission of measles from cases with breakthrough infections in household settings. However, we do not conclude that the risk of measles transmission is limited to unvaccinated cases, but rather that ” …there was a large difference in viral load in nasopharyngeal samples between patients with naïve and breakthrough infections of measles, and our results indicate that a high risk of onward transmission is confined to naïve infections ” [1]. Thus, with our definition of breakthrough infection (history of vaccination and detectable IgG (high avidity) at rash onset (or within 4 days)), the risk of onward transmission is low in most cases.…”

The digital immunization system of the future: imagining a patient-centric, interoperable immunization information system

“…45 Reductions in vaccine coverage for a variety of reasons have resulted in the resurgence of vaccine-preventable diseases – most notably measles – with important health consequences. 46 – 51 Given the breadth and complexity of factors at play, public health officials need to find innovative ways to address individual immunization knowledge, attitudes, and beliefs, which are intrinsically linked to their healthcare providers and surrounding environment. 52 – 54 The European Vaccine Action Plan 2015–2020 etches this sentiment as it identifies tailored, innovative strategies as critical in reaching population groups with suboptimal vaccination coverage.…”