Mosquito nets save lives. So why is VC Marc Andreessen against them?

The no good, very bad case against malaria bednets, explained.

A young boy wearing a red shirt rolls up a white mosquito net covering bedding at a South Sudan refugee camp. Behind him is a makeshift fence of sticks separating the sleeping area from nearby bushes.
A young boy rolls up a mosquito net covering bedding at a refugee camp in 2023 in South Sudan.
Luke Dray/Getty Images

Dylan Matthews is a senior correspondent and head writer for Vox’s Future Perfect section and has worked at Vox since 2014. He is particularly interested in global health and pandemic prevention, anti-poverty efforts, economic policy and theory, and conflicts about the right way to do philanthropy.

Marc Andreessen, the billionaire venture capitalist and early web browser developer, thinks we’re giving too many insecticidal bednets to people exposed to malaria, tweeting, “Mosquito nets are a triple threat — dangerous to people, dangerous to fish, and dangerous to fishing ecosystems and the communities they feed.”

That mosquito nets are dangerous to people would be news to basically any public health professional who’s ever studied them. A systematic review by the Cochrane Collaboration, probably the most respected reviewer of evidence on medical issues, found that across five different randomized studies, insecticide-treated nets reduce child mortality from all causes by 17 percent, and save 5.6 lives for every 1,000 children protected by nets. That implies that the 282 million nets distributed in 2022 alone saved about 1.58 million lives. In one year.

So … what the hell is Andreessen even talking about?

To understand why someone who has historically been more interested in crypto art than global health is suddenly tweeting about malaria, you have to know a little bit about Andreessen’s grudges. Andreessen’s VC firm, Andreessen Horowitz (a16z), has invested in a lot in AI companies lately, and he has aligned himself with a faction known as “effective accelerationists,” who favor aggressive progress in AI with minimal regulation or guardrails.

The effective accelerationists, or e/acc, define themselves in large part by their opposition to effective altruists, the social movement that began by focusing on cost-effective global health interventions and has more recently advocated for tough regulations to prevent AI from going awry (Future Perfect, the section running this article, is broadly inspired by EA ideas). Effective altruists have long been identified with anti-malarial bednets, a prime example of the very cheap, very effective global health causes they favor.

So, largely to stick it to the people who want AI regulation, Andreessen has committed himself to attacking one of the best methods of preventing malaria. If that doesn’t make sense to you, don’t worry; you’re not the one acting ridiculous.

But it’s worth taking the critique here at least marginally seriously. Do bednets have serious downsides, related to misuse for fishing, that their advocates are simply ignoring?

In a word: no. In multiple words: The finding that bednets save lives is not affected, at all, by the minority of people who use bednets to fish, rather than to protect themselves from malaria. Some of these people use nets that are several years old with insecticide that’s worn off, and are no longer effective at killing mosquitos. There is little research on what fishing with these nets actually does to fish or people — but also little reason to think the magnitudes of these effects are remotely near the number of lives saved by nets.

Bednets and fishing nets

Andreessen’s objection is rooted in something that’s been true of bednets for decades: sometimes, people use them as fishing nets instead.

This has occasionally popped up as an objection to bednet programs, notably in a 2015 New York Times article. One related argument is that the diversion of nets toward fishing means they’re not as effective an anti-malaria program as they initially appear.

That’s simply a misunderstanding of how the research on bednets works. The scientists who study these programs, and the charities that operate them, are well aware that some share of people who get the nets don’t use them for their intended purpose.

The Against Malaria Foundation, for instance, a charity that funds net distribution in poor countries, conducts extensive “post-distribution monitoring,” sending surveyors into villages that get the nets and having them count up the nets they find hanging in people’s houses, compared to the number previously distributed. When conducted six to 11 months after distribution, they find that about 68 percent of nets are hanging up as they’re supposed to; the percent gradually falls over the years, and by the third year the nets have lost much of their effectiveness.

So does this mean that bednets are only 68 percent as effective as previously estimated? No. Studies of bednet programs do not assume full takeup, because that would be a dumb thing to assume. Instead, they evaluate programs where some villages or households randomly get free bednets, and compare outcomes (like mortality or malaria cases) between the treated people who got the nets and untreated people who didn’t.

For instance, take a 2003 paper evaluating a randomized trial of net distribution in Kenya (this was one of the papers included in the Cochrane review). The researchers’ own surveys show that about 66 percent of nets were used as intended. The researchers did not exclude the one-third of households not using the nets from the study. Instead, they simply compared death rates and other metrics in the villages randomized to receive nets to those metrics in villages randomized to not get them. That comparison already bakes in the fact that a third of households who received the nets weren’t using them.

So estimates like “bednets reduce child mortality by 17 percent” are already assuming that not everybody is using the nets as intended. This just isn’t a problem for the impact estimates.

But is it a problem for fisheries? Andreessen cites one recent article to make this case. It’s not clear to me he actually read it.

The authors start by acknowledging that bednets have saved millions of lives, and even that the use of nets for fishing makes sense for many people. It’s a free way to get food you need to survive in regions often reliant on subsistence farming. Moreover, the authors note that “The worldwide collapse of tropical inland freshwater fisheries is well documented and occurred before the scale-up of ITNs.” At worst, you can accuse nets of making an existing problem worse.

The bigger question the authors raise is that insecticides are toxic. That’s, of course, the point: They’re meant to kill mosquitoes. The question, then, is whether they are toxic to fish or humans when used for fishing. The authors’ conclusion is maybe, but we have no research indicating one way or another. “To our knowledge there is currently a complete lack of data to assess the potential risks associated with pyrethroid insecticide leaching from ITNs,” the authors conclude. They are not sure if the amount leaching from nets is enough to be toxic to fish; they’re not fully sure that the insecticide leaches into the water at all, though they suspect it does. Even less clear is how these insecticides might affect humans who then eat fish that might be exposed to them.

I asked the study’s lead author, David Larsen, chair of the department of public health at Syracuse’s Falk College of Sport & Human Dynamics and an expert on malaria and mosquito-borne illnesses, for his reaction to Andreessen citing his work. He found the idea that one should stop using bednets because of the issues the paper raises ridiculous:

Andreessen is missing a lot of the nuance. In another study we discussed with traditional leaders the damage they thought ITNs [insecticide-treated nets] were doing to the fisheries. Although the traditional leaders attributed fishery decline to ITN fishing, they were adamant that the ITNs must continue. Malaria is a scourge, and controlling malaria should be the priority. In 2015 ITNs were estimated to have saved more than 10 million lives — likely 20-25 million at this point.

… ITNs are perhaps the most impactful medical intervention of this century. Is there another intervention that has saved so many lives? Maybe the COVID-19 vaccine. ITNs are hugely effective at reducing malaria transmission, and malaria is one of the most impactful pathogens on humanity. My thought is that local communities should decide for themselves through their processes. They should know the potential risk that ITN fishing poses, but they also experience the real risk of malaria transmission.

He notes that the fish toxicity issue is real and worth investigating further; a colleague, the University of Florida’s Joe Bisesi, is investigating this and, preliminarily, the insecticide does seem to harm fish. Just because an intervention like bednets is effective at its primary purpose doesn’t mean it doesn’t have unintended consequences, and it’s worth investigating those fully.

But, as Larsen says, people like him, me, and Andreessen aren’t the people affected here. The people affected, in rural Africa and other malarial regions, overwhelmingly want bednets as a tool to help them survive.

Put your money where your mouth is

Luckily for Andreessen and like-minded folks, people genuinely worried about fisheries and insecticidal toxicity in Africa have other options. They can support the Malaria Consortium, for instance, which instead of bednets offers seasonal chemoprevention, an approach in which people in malarial regions get preventive medicines meant to reduce their risk of infections. If you’ve traveled to a malarial region, you may have gotten these drugs yourself from a travel medicine clinic; I did before a trip to Burma. There are no fishing-related concerns with chemoprevention, and it also saves lives very cost-effectively.

One could also fund work on malaria vaccines. The R21 vaccine, recently approved by the World Health Organization, is 75 percent effective against infection, and stakeholders like the vaccine distribution group GAVI and the Global Fund to Fight AIDS, Tuberculosis and Malaria are currently working out a plan to fund a mass rollout. Bednet skeptics could easily donate to those groups, or fund advocacy to get governments like the US to increase their commitments to the Global Fund and GAVI to ensure the vaccination effort is adequately funded.

The broader point Andreessen was trying to make by attacking bednets, in his words, was that, “It is very, very hard to intervene in other people’s lives — particularly from a distance — and not make things worse.” It is indeed really hard, and requires a lot of research — but luckily people have done that research, and even if for whatever reason bednets don’t clear the bar for you, there are plenty of effective interventions against malaria and other diseases that don’t raise any issues around fishing.

The question, then, is whether that moves you to support these causes, or if attacking bednets is just an excuse for one’s own inaction. I don’t know Andreessen’s own donation history; maybe he’s been giving to the Malaria Consortium this whole time. If so, god bless. If not, he should consider taking his own arguments a bit more seriously.


No votes yet.
Please wait...

Leave a Reply

Your email address will not be published. Required fields are marked *