Pox parties, also known as flu parties, are social activities in which children are deliberately exposed to infectious diseases such as chickenpox. Such parties originated to "get it over with" before vaccines were available for a particular illness or because childhood infection might be less severe than infection during adulthood, according to proponents. For example, measles is more dangerous to adults than to children over five years old. Deliberately exposing people to diseases has since been discouraged by public health officials in favor of vaccination, which has caused a decline in the practice of pox parties, although flu parties saw a resurgence in the early 2010s.

Parents who expose their children to varicella zoster virus in this manner often do so out of the belief that acquiring immunity to chickenpox via infection is safer and more effective than receiving a vaccination. Similar ideas have been applied to other diseases such as measles. Pediatricians have warned against holding pox parties, however, citing dangers arising from possible complications associated with chickenpox, such as encephalitis, chickenpox-associated pneumonia, and invasive group A strep. These serious complications (e.g., brain damage or death) are vastly more likely than vaccine adverse events. Before the chickenpox vaccine became available, 100 to 150 children in the U.S. died from chickenpox annually. In the UK, chickenpox vaccinations are not routine, and around 25 people die a year from the disease, with 80% of victims being adults, in the late 1990s. The chickenpox vaccine is now recommended by health officials, citing vastly superior safety when compared with infection.

Some parents have attempted to collect infectious materials, such as saliva, licked lollipops, or other infected items from people who claimed to have children infected with chickenpox. Others use social networking services to make contact with these strangers. The unknown person then mails the potentially infectious matter to the parent, who would then give it to their child in the hope that the child will become infected.

These practices are unlikely to reliably transmit the chickenpox virus because varicella zoster cannot survive for long on the surface of such items. Those items can, however, transmit other diseases, including hepatitis B, group A streptococcal infection, and staphylococcal infections — dangerous diseases to which the parents never intended to expose their children. Additionally, in the United States, deliberately sending infectious matter through the U.S. Postal Service is illegal.

While chickenpox parties are still held today, they are far less common than before the chickenpox vaccine was introduced.

In the United States, chickenpox parties were popularized before the introduction of the varicella vaccine in 1995. Children were also sometimes intentionally exposed to other common childhood illnesses, such as mumps and measles. Before vaccines for these infections became available, parents regarded these diseases as almost inevitable.^{[full citation needed]}

During the 2009 swine flu pandemic in Canada, doctors noted an increase in what was termed flu parties or flu flings. These gatherings, as with the pox parties, were designed explicitly to allow a parent's children to contract the "swine flu" influenza virus. Researchers such as Dr. Michael Gardam noted that because the pandemic was caused by a flu subtype to which very few people were previously exposed, parents would be just as likely to contract the disease and further its spread. Although these events were heavily discussed in the media, very few were confirmed to have happened.

A COVID-19 party (also called coronavirus party, corona party, and lockdown party) is a gathering held with the intention of catching or spreading COVID-19. It is a type of pox party where the intentional spread of disease is chosen to build up post-infection immunity. Parties have been reported to occur during the omicron wave, due to the belief that omicron causes only mild infection. Experts caution that infection with COVID runs the risk of hospitalization, and increasingly common side effects such as MIS-C and long COVID.