New evidence has emerged that Robert F Kennedy Jr was on a vaccine-related “mission” when he visited Samoa ahead of a deadly measles outbreak in 2019, raising further questions about whether the US health secretary lied to the US Senate when he said the trip had “nothing to do with vaccines”.

Records obtained by the Guardian show Kennedy’s colleague told Samoan officials in an email that he and Kennedy were coming as part of a mission to study the island nation’s medical records in the aftermath of a “discontinuity in vaccinations”.

“We all look forward to the opportunity to be of service to the people of Samoa with our mission,” Dr Michael Graven wrote.

Kennedy was at the time serving as chair and chief legal counsel of Children’s Health Defense, a non-profit group known for its anti-vaccine activism. Graven was the group’s chief information officer. Spokespeople for Kennedy at the US Department of Health and Human Services (HHS) did not respond to messages seeking comment.

Kennedy’s trip to the Pacific island nation is among the most heavily criticized activities he undertook before being named health secretary by Donald Trump. Kennedy has frequently claimed that his reason for going to Samoa was not about vaccines and that his visit did not influence people’s decisions on whether to vaccinate. At his Senate confirmation hearing last year, he said: “You cannot find a single Samoan who will say I didn’t get a vaccine because of Bobby Kennedy.” Instead, he said he went to attend a Samoan independence celebration and to introduce a “state-of-the art” medical informatics system.

Samoan officials later said Kennedy’s visit bolstered the credibility of anti-vaccine activists. A measles outbreak, which tore through the Pacific island nation a few months after Kennedy’s visit, sickened thousands and killed 83 people, mostly children under age five.

Earlier this year, the Guardian and the Associated Press obtained emails from US government and Unicef officials that undermined Kennedy’s claims about why he visited Samoa. That prompted two Democratic senators and a member of the House to say the reporting showed Kennedy lied to the Senate.

The US Department of State has been turning over the emails – many heavily redacted – in batches since January as a result of an open records lawsuit brought with the assistance of the Reporters Committee for Freedom of the Press.

Anti-vaccine activists in the US became interested in Samoa when two infants died in 2018 after they were injected with a tainted measles, mumps and rubella vaccine that was improperly prepared. The government halted all vaccinations for 10 months, until April 2019, and vaccination rates plummeted. During that time, Kennedy’s group Children’s Health Defense started reaching out to the Samoan government, according to emails previously obtained by the Guardian and the AP.

Despite the evidence that vaccines are safe and have saved millions of lives, Kennedy has long called for studies in which some children would not be immunized in order to compare the health of vaccinated children against unvaccinated children. Samoa’s pause would have provided such an opportunity.

By the time Kennedy arrived on 30 May 2019, vaccinations had resumed, but rates were still very low.

Emails released by the state department show Graven traded messages with Samoan officials before he, Kennedy and Kennedy’s wife, the Curb Your Enthusiasm actor Cheryl Hines, traveled there.

In one email dated 8 March 2019, Graven said he would “be with Mr Kennedy as the Health Informatician who will be performing the statistical investigations”.

He went into more detail two months later in a message on 13 May by saying he was sending it “after discussion with” Kennedy and describing the trip several times as a “mission”.

“The mission involves health informatics evaluation from medical record data from all hospitals and clinics in Samoa to evaluate outcomes associated with the recent discontinuity in vaccinations,” Graven wrote. “Mr Kennedy asked me to join this mission as I have performed health informatics initiatives in 48 other countries over 40 years.”

Graven, a pediatrician who died in 2022, described collecting data and doing a statistical analysis, saying he planned to travel to all hospitals and clinics in Samoa.

He said the mission would be conducted “without bias”, adding that he had witnessed the harmful effects of vaccine-preventable illness, and that he also had served countries where they had discovered “bad vaccine lots”.

Graven’s description of their work stands in contrast to Kennedy’s comments before the Senate last year, when he repeatedly denied the trip had anything to do with vaccines. In questioning from Ron Wyden, a senator from Oregon, Kennedy said: “I went there, nothing to do with vaccines. I went there to introduce a medical informatics system with digitalized records in Samoa and make health delivery much more efficient.”

The following day, under questioning by Edward Markey, of Massachusetts, Kennedy said: “My purpose in going down there had nothing to do with vaccines.”

Upon further questioning, Kennedy again denied it had anything to do with vaccines before adding: “My purpose in the trip was not to – I ended up having conversations with people, some of whom I never intended to meet.”

Kennedy went on to say that Children’s Health Defense had a $6m grant “to digitalize the health records of Samoa … and to bring in a state-of-the-art medical informatic system” to the island nation. This was “the purpose” of his trip, Kennedy said.

In the records obtained by the Guardian, Graven said in emails in March and May that he planned to spend weeks visiting sites and collecting and analyzing data. But an email that Antone Greubel, a state department employee stationed in Samoa, sent to colleagues on 4 June said Graven left with Kennedy a few days after arriving.

“Based on conversations with my contacts RFK and Dr [Graven] fell far short of their goal to influence Samoan government vaccination policy,” Greubel wrote.

The emails provide the most detailed view yet on Kennedy’s trip to Samoa and suggest it was connected to his longstanding interest in scientific studies that compare the health of vaccinated people with those who are unvaccinated. Children’s Health Defense did not respond to a request for comment.

Kennedy’s 2023 book, Vax-UnVax: Let the Science Speak, called for more studies comparing the health of fully vaccinated children with those who are not vaccinated. The New York Times reported this month that in his role as health secretary, Kennedy has asked government scientists to undertake such studies, which he believes will prove vaccines are harmful. And last year, the US Centers for Disease Control and Prevention (CDC) granted funding to a study that would have compared the health of children who were vaccinated with the hepatitis B vaccine with children who had not received it in Guinea-Bissau. It was deemed unethical by the head of the World Health Organization and others and was paused.

Wyden said in response to questions from the Guardian that the new findings “offer more proof that Robert Kennedy is a liar on a mission to take vaccines away from kids who need them”.

“Republicans have turned a blind eye to Kennedy’s anti-vaccine crusade and abdicated their responsibility to hold those who lie to Congress accountable. Democrats will not hesitate to use every available tool to thwart the Trump administration’s healthcare agenda that is making America sicker and poorer.”

In a 2021 blog post, Kennedy wrote that he went to Samoa to discuss “the introduction of a medical informatics system” to track drug safety. He suggested in that post that it was Samoan officials who “were curious to measure health outcomes following the ‘natural experiment’ created by the national respite from vaccines”.