Attenuated vaccine in the context of "Inactivated vaccine"

Polio vaccine is a vaccine used to prevent poliomyelitis (polio). Two types are used: an inactivated poliovirus given by injection (IPV) and a weakened poliovirus given by mouth (OPV). The World Health Organization (WHO) recommends all children be fully vaccinated against polio. The two vaccines have eliminated polio from most of the world, and reduced the number of cases reported each year from an estimated 350,000 in 1988 to 33 in 2018.

The inactivated polio vaccines are very safe. Mild redness or pain may occur at the site of injection. Oral polio vaccines cause about three cases of vaccine-associated paralytic poliomyelitis per million doses given. This compares with 5,000 cases per million who are paralysed following a polio infection. Both types of vaccine are generally safe to give during pregnancy and in those who have HIV/AIDS, but are otherwise well. However, the emergence of circulating vaccine-derived poliovirus (cVDPV), a form of the vaccine virus that has reverted to causing poliomyelitis, has led to the development of novel oral polio vaccine type 2 (nOPV2), which aims to make the vaccine safer and thus stop further outbreaks of cVDPV.

Polio eradication, the goal of permanent global cessation of circulation of the poliovirus and hence elimination of the poliomyelitis (polio) it causes, is the aim of a multinational public health effort begun in 1988, led by the World Health Organization (WHO), the United Nations Children's Fund (UNICEF) and the Rotary Foundation. These organizations, along with the U.S. Centers for Disease Control and Prevention (CDC) and The Gates Foundation, have spearheaded the campaign through the Global Polio Eradication Initiative (GPEI). Successful eradication of infectious diseases has been achieved twice before, with smallpox in humans and rinderpest in ruminants.

Prevention of disease spread is accomplished by vaccination. There are two kinds of polio vaccine—oral polio vaccine (OPV), which uses weakened poliovirus, and inactivated polio vaccine (IPV), which is injected. OPV is less expensive and easier to administer, and can spread immunity beyond the person vaccinated, creating contact immunity. It has been the predominant vaccine used. However, under conditions of long-term vaccine virus circulation in under-vaccinated populations, mutations can reactivate the virus to produce a polio-inducing strain, while OPV can also, in rare circumstances, induce polio or persistent asymptomatic infection in vaccinated individuals, particularly those who are immunodeficient. IPV, being inactivated, does not carry these risks, but does not induce contact immunity. IPV is more costly and the logistics of its delivery are more challenging.

The 1977 Russian flu was an influenza pandemic that was first reported by the Soviet Union in 1977 and lasted until 1979. The outbreak in northern China started in May 1977, slightly earlier than that in the Soviet Union. The pandemic mostly affected a population younger than 25 or 26 years of age, and was described as mild. It was caused by an H1N1 flu strain which highly resembled a virus strain circulating worldwide from 1946 to 1957. Genetic analysis and several unusual characteristics of the 1977 Russian flu have prompted many researchers to say that the virus was released to the public through a laboratory accident, or resulted from a live-vaccine trial escape.

The Russian flu first reached the United Kingdom in 1977, and the United States in January 1978. The first outbreak in the United States took place in Cheyenne, Wyoming, but more than 70% of those infected were students. The flu spread in schools and military bases throughout the United States, but most of those infected were below the age of 26. In the United States, the death rate in affected individuals was low.