Antivaxxers like to talk about "doing the research," but seem woefully inept at interpreting evidence. They depend entirely on what the author claims to have done. But, that's not evidence: authors can say whatever they wish; we should care about what they show.

Here's a paper often claimed to prove that kids vaccinated for measles "shed" the vaccine-strain virus. The abstract even mentions it. But, is this what the paper actually shows? Let's go through the evidence.

https://jcm.asm.org/content/33/9/2485.long

First: methods. Measles is an RNA virus: when it replicates, it stores its genetic code in RNA. The authors wanted to demonstrate an easy way to rapidly detect infection by detecting the presence of measles RNA.

The authors collected urine from children and adults, and used a technique called RT-PCR to detect presence of measles RNA. This technique will find measles RNA, and, if it's present, make many, many copies of a portion of it.

This is visible as a "band" of color when stained with a chemical, ethidium bromide. A more sensitive detection method is to use film. The authors do both. Now, before we actually look at the evidence, I want you to ask yourself: can this method detect the presence of a virus?

The authors gave MMR to children and adults, then collected urine to see if they could detect measles RNA. They also looked for a human RNA to determine if absence of measles RNA was just because of a breakdown of any and all RNA in the urine.

12 kids were given MMR. They could detect measles RNA 10 of the 12 children at some point within 2 weeks of vaccination. 4 young adults were given MMR boosters. Measles RNA was detected in all 4.

So, what does this tell us, exactly?

What are the authors actually looking for here? They are looking for the presence of a fragment of measles genome in urine. Could that test ever tell us if the person was shedding infectious virus? To be infectious, the entire measles genome must be wrapped in a shell, a capsid.

It is also a respiratory infection and must be breathed in. Can we tell if that is happening here?

If we see a positive urine sample, what does that tell us? That there is likely measles infection, yes. But does it tell us if any infectious virus is actually being made?

If we see a negative urine sample, what does that tell us? That maybe the kid isn't infectious. Given that no RNA was ever detected in 2 kids who presumably had active vaccine-strain measles infection, a negative result isn't necessarily conclusive.

Do either of these results tell us if the kid is producing complete viruses that they are sneezing out? No. Could that be occurring? Maybe, but there is no evidence provided one way or the other.

This paper is not evidence of MMR causing infectious virus shedding. It is evidence that recently vaccinated kids pee out measles RNA that may or may not be intact. That's it, because that's all it could ever say given the tests used.

When you're reading a paper, you need to always keep in mind the question the authors want to answer and whether they were actually able to answer it given the tests used. If you're looking for infectious virus, you need to actually look for infectious virus (eg, a plaque assay).

But, that's not really what the authors were trying to do here. They were attempting to find a cheaper, easier alternative to detect *infection.* This is not the same as *infectious.*