By April 4, the US Centers for Disease Control and Prevention had already reported 465 cases of measles, more than the total for all of 2018.

While measles is concerning in its own right, an overlooked detail adds another layer to the threat, says Katherine Kirk, a Master of International Affairs candidate at Columbia University's School of International and Public Affairs.

In the US, there is an ongoing Russian disinformation campaign that could make Americans hesitant to vaccinate their children.

Moscow's goal, says Kirk, has never been to advantage Republicans or Democrats.

Instead, it seeks to exacerbate Americans' distrust of one another and, in turn, erode their confidence in society and the US government.

In recent weeks, public health officials and state legislators have scrambled to combat new cases of measles across the United States. By April 4, the US Centers for Disease Control and Prevention had already reported 465 cases of the disease, more than the total for all of 2018.

Measles is concerning in its own right. Aside from the discomfort it causes, in 25% of cases people who get measles are hospitalized. But an overlooked detail adds another layer to the threat. In the United States, measles has a surprising booster: Russian trolls and bots.

The existence of a Russian disinformation campaign that could make Americans hesitant to vaccinate their children highlights something important about the Kremlin's information war on the United States. Moscow's goal has never been to advantage Republicans or Democrats.

Read more: From autism risks to mercury poisoning, here are 10 lies anti-vaxxers are spreading about the measles vaccine

Instead, it is after a far bigger prize: the exacerbation of Americans' distrust of one another and, in turn, the erosion of their confidence in society and the US government.

Thousands of Russian accounts spread disinformation and anti-vaccine messaging

A recent study from David Broniatowski, a professor at George Washington University, and his co-authors found that thousands of Russian accounts used to spread disinformation had seized on anti-vaccine messaging.

After combing through nearly 2 million tweets recorded between 2014 and 2017, the researchers found that Russian troll accounts were significantly more likely to tweet about vaccination than general Twitter users. They had turned to vaccines as a wedge issue in an effort to ramp up social discord, erode trust in public health institutions, and exacerbate fear and division in the United States.

Russian trolls and bots turned to vaccines as a wedge issue in an effort to ramp up social discord. Getty Imges/Joe Raedle Three tweets from the study go a long way toward capturing the style of this disorienting campaign. In one round of keystrokes, a Russian-backed account lashed out: "#vaccines are a parent's choice. Choice of a color of a little coffin #VaccinateUS."

Another went with: "Did you know there was a secret government database of #vaccine-damaged children? #VaccinateUS."

Read more: Inside 'vaccine court,' where the US government pays millions to people who say they were harmed by vaccines

Moving toward the opposite pole of the discussion, a Russian troll account tweeted: "Do you still treat your kids with leaves? No? And why don't you #vaccinate them? Its medicine! #VaccinateUS." The study suggested that by giving the illusion of a grassroots debate, complete with content pushing both for and against vaccination, Russia could better tap into the fears and divisions among Americans — and exploit them.

A history of campaigns on US public health

This isn't the first time Russian information warfare campaigns have focused on US public health. One of the most successful Soviet disinformation efforts, codenamed Operation Infektion, set out to push a false narrative that the HIV virus had been created by the US government at Fort Detrick, Maryland, for the explicit purpose of targeting black and gay people in the United States and abroad.

Operation Infektion's first volley was a piece published in an English-language newspaper in India in July 1983. The arguments were then spread throughout the world through a series of KGB initiatives. By 1987, CBS News had covered the claim. Not only did this effort tarnish America's reputation abroad — and weaken the ability of the United States to work with foreign governments to address the HIV crisis — but it also attempted to stoke Americans' distrust in their own government.

In this Aug. 1963 photo, a technician working under sterile conditions stores trays of living cell tissue in an incubator at the virus laboratories of Chas. Pfizer & Co. in Terre Haute, Indiana. Cells are nurtured to serve as hosts for live virus needed for the measles vaccine. AP Photo And that gambit worked. In 1992, 15% of Americans agreed that it was definitely or probably the case that HIV was "created deliberately in a government laboratory." The effect was particularly strong among one of the Soviets' key targets: African Americans. A 2005 study by the Rand Corp. and Oregon State University found that more than 25% of African Americans who were surveyed considered HIV to be the product of a government lab.

Russia's efforts to spread disinformation about vaccines have taken some pages out of that old playbook. Russian trolls' contemporary messages were crafted with key terms like "freedom" and "constitutional rights," which were often absent from other anti-vaccination tweets. One Russian disinformation account captured the style of this approach in just 13 words and two hashtags: "Apparently only the elite get 'clean' #vaccines. And what do we, normal ppl, get?! #VaccinateUS."

Read more: What every 2020 presidential candidate has said about vaccines

So far, Russia's vaccine-related disinformation efforts have had ambiguous results when it comes to measles vaccine uptake. As the journalist Daniel Engber recently emphasized, outbreaks remain isolated among pockets where community vaccination rates have fallen below protective levels.

Overall, though, vaccination rates for measles, mumps, and rubella have remained stable at around 91.5% for children aged 3 and under since 2005. Even with the panic and fear surrounding the current outbreaks, measles still remains under control in the United States at present.

Yet panic over the anti-vaxxer movement and its potential impact on public health remains. Russian disinformation activities, which have tried to amplify and intensify the debate between pro-vaccine and anti-vaccine activists, have contributed to the illusion of a growing anti-vaxxer movement while also sowing distrust among Americans.

In turn, although this information operation may not have changed US vaccination rates, it has successfully identified two critical vulnerabilities — inequality and distrust in the public health system.

Russian disinformation campaigns seek to target multiple US vulnerabilities

Another source of US vulnerabilities that Russian disinformation campaigns are looking to take advantage of centers on the country's foreign policy. Take Syria, for example. Researchers recently released a dataset of 3 million tweets from Russian trolls gathered and published by Clemson University in partnership with FiveThirtyEight.

The word "Syria" appeared in nearly 19,000 of them. A preliminary analysis revealed that Russian troll accounts frequently targeted audiences on both sides of the political spectrum to criticize US engagement in Syria. It wasn't uncommon for the same account to alternate between addressing audiences on the right and left.

US-backed Syrian Democratic Forces (SDF) stand in formation at a ceremony to mark their defeat of Islamic State militants in Baghouz, at al-Omar Oil Field base, Syria, Saturday, March 23, 2019. Associated Press Although the specific messaging used to engage different audiences varied, the overall Russian narrative appears to be one built around US incompetence and malfeasance. Its messaging aligned clearly with Russia's foreign-policy objective of limiting US involvement in Syria.

It is unclear whether Russian trolling has shaped public opinion along these lines, an issue on which the country remains highly divided. But Russian trolls' success covertly engaging with Americans of every political persuasion on this issue reveals a clear US vulnerability to foreign influence.

Despite evidence that the vaccine campaign and the Syria campaign targeted both Republicans and Democrats, Americans still believe that Russia's disinformation efforts are overwhelmingly partisan. In part, that is because of the Russian information warfare operations during the 2016 US presidential election, which supported the presidency of Donald Trump.

While the net effect was unambiguously pro-Trump, however, that had far less to do with Russian affinity for the Republican Party than it did with Russian policymakers' belief that, given the roster of candidates, a Trump victory would best suit their interests.

As the 2020 election approaches, Russia's approach may shift again.

Russian trolls' success covertly engaging with Americans of every political persuasion on this issue reveals a clear US vulnerability to foreign influence. Reuters Indeed, some of the Kremlin's early propaganda efforts have promoted the candidacy of Rep. Tulsi Gabbard, which likely stems from the belief that she supports the preservation of Bashar al-Assad's regime in Syria. Given Gabbard's divergence from the majority of Democrats on key social and foreign-policy issues, Russian support for her candidacy mimics its support of Trump in 2016 as a divisive outsider.

Russia isn't interested in the final outcome of US partisan struggles. It is interested in identifying, targeting, and amplifying any vulnerabilities of the United States. Efforts to use vaccination as a wedge issue demonstrates just how well Russian information operations can take any issue, identify how it may engage or divide Americans, and manipulate social media discourse to meet Russian ends.

Russia continues to employ a disparate network of people and technological tools in order to make Americans turn on one another, their political leaders, their democratic institutions, and even on foundational public health innovations.

To counter Russian information operations online in the long run, the United States should resist partisan approaches to the issue, which ultimately play into Russia's hands. Rather, it must make a credible attempt to address the fundamental divisions in its society that Russia has found it worthwhile to exploit. Only by mending its social cleavages can the United States develop long-term resilience against the machinations of Russian information warfare.

Katherine Kirk is a Master of International Affairs candidate at Columbia University's School of International and Public Affairs.