A study finds that paying people to take a first dose of a COVID-19 vaccine didn't lower the likelihood of seeking the second or third dose or of other positive health behaviors and didn't erode morals, sense of civic duty, or feelings of self-determination.

The study, led by Swiss and Swedish researchers, was published yesterday in Nature. The researchers note that, while financial incentives to encourage healthy and prosocial behaviors often generate initial behavioral change, critics say that they can corrode prosocial motivations, lead to moral decay, and increase feelings of coercion, reducing the likelihood of practicing healthy behaviors without a payment.

The team offered 1,131 Swedish participants in a previous randomized, controlled trial (RCT) 200 Swedish krona (SEK), or roughly $24 US, to receive a first COVID-19 vaccine dose within 30 days. That group was compared with 3,888 matched participants not offered the incentive.

Just as likely to seek subsequent doses

The researchers combined the RCT data with vaccination records on second-dose uptake and survey results from January (first dose uptake) and June 2022 (third dose). A total of 726 participants in the financial incentive group and 2,512 controls responded to the first survey, and 606 and 2,100, respectively, completed the second.

The payment boosted uptake by 4 percentage points 30 days after the trial ended. Uptake remained elevated for at least 3 months.

The authors identified no negative effects of financial incentives on subsequent planned or actual COVID-19 vaccine uptake or timing, morals, sense of civic duty, trust in vaccination providers or in the safety and effectiveness of vaccines, attitudes toward financial incentives, or feelings of self-determination or coercion.

Nor was there evidence that incentives received in the previous 5 months for behaviors such as flu shot uptake or blood donation had any negative effects on the decision to receive the COVID-19 vaccine. "Our findings inform not only the academic debate on financial incentives for behaviour change but also policy-makers who consider using financial incentives to change behaviour," they wrote.

A small new study—this one analyzing antibodies in infants' stool samples—provides further evidence that the breast milk of women vaccinated against COVID-19 may help protect babies who are too young to receive the vaccine, according to findings published today in the Journal of Perinatology.

Using neutralization assays, University of Florida researchers found higher levels of immunoglobulin A and G (IgA and IgG) antibodies against SARS-CoV-2 in the stool of infants of breastfeeding mothers compared with those who breastfed from unvaccinated moms. The study involved 34 mothers and 24 infants.

The study also measured and tested antibodies found in the mothers' blood plasma and breast milk soon after vaccination and about 6 months later. The investigators found that the antibodies in the plasma and milk of vaccinated women were better able to neutralize the virus than those of unvaccinated women. Antibody levels decreased at 6 months, as has been noted previously.

This study follows up on a December 2021 study that revealed significant secretion of SARS-CoV-2–specific IgA and IgG in the milk and plasma of breastfeeding women after SARS-CoV-2 vaccination, but that study did not involve infant stool sampling.

Next step: assessing protection

"Our first study showed there were SARS-CoV-2 antibodies in the breast milk, but we couldn't say if those antibodies were getting through the babies' gastrointestinal tract and possibly providing protection there," said Joseph Larkin III, PhD, senior author of today's study, in a university news release.

Commenting on the new study, coauthor Vivian Valcarce, MD, said, "The antibodies ingested through breast milk may provide a protective coating in the infants' mouths and gastrointestinal tract."

We're following the journey of the antibodies.

Josef Neu, MD, another coauthor, added, "We're following the journey of the antibodies, from the time they are produced in mom after vaccination and now through the baby's digestive system. The next question is whether those babies are less likely to get COVID-19."

The study was funded by grants from the Children's Miracle Network and The Gerber Foundation.