Take 404 people with low immunity to a flu virus
Phone them each evening for two weeks to ask whether they were involved in any interpersonal tension or conflict during the day and whether anyone had hugged them that day
Quarantine them three weeks later by keeping them in a room on their own in a local hotel
On the first day of quarantine, take a blood sample and a nasal wash specimen to measure antibody levels and look for any existing virus
On each day, for the next five days, give them nasal drops designed to infect them with viruses that will give them a cold. Also on each of these five days assess them for nasal mucus production, and use a nasal-wash samples to look for virus culture
Release them from quarantine after 5 days
Collect more blood 28 days later, to re-test antibody levels
The people who reported being hugged more frequently were significantly less likely to develop infection. The way this worked was that, people experiencing more tension were generally at a greater risk of infection, but the more hugs received, the less likely this tension was to cause infection.
At the moment, it's not clear whether the benefit from hugging is due to the physical contact itself or because hugging is a indicator of support and intimacy. Either way, people who receive more hugs are less likely to get ill.