What is a 'breakthrough infection' that infects corona even in people who have completed vaccination?

Cases of developing a new coronavirus infection (COVID-19) have been reported despite the completion of vaccination with the new coronavirus.

The Centers for Disease Control and Prevention (CDC) has called this case 'vaccine breakthrough cases' and is calling for caution, but what are the characteristics of the breakthrough infection? Inverse explains.

What You Should Know About the Possibility of COVID-19 Illness After Vaccination | CDC

Delta variant: 8 things vaccinated people should know about breakthrough Covid-19

'The war has changed': Internal CDC document urges new messaging, warns delta infections more likely more severe --The Washington Post

◆ What is a breakthrough infection?
The CDC 'from in respiratory specimens of people who completed the vaccination of vaccine that has been approved by the FDA, RNA or antigen of the new coronavirus (SARS-CoV-2) are cases that have been detected' a break-through infection and not in association definition I will . In the guidance for those who have completed vaccination , the CDC defines 'completion of vaccination' as 'two vaccines developed by Pfizer & BioNTech and Moderna for more than two weeks after being vaccinated twice. 'Timing has passed' 'The Johnson End Johnson (J & J) vaccine is the timing when more than two weeks have passed since the first inoculation.'

'People who complete vaccination have a reduced risk of SARS-CoV-2 infection, aggravation, and death,' the CDC said in the same guidance. However, 'it tends to be mild, but breakthrough infection occurs only in a small part.' 'If you are infected with the highly infectious Delta strain (B.1.617.2) , you can infect other people. It is recommended to those who have completed vaccination, such as 'wear a mask even indoors in areas with high infection rates' and 'take a test if symptoms of COVID-19 appear'. doing.

◆ How many breakthrough infections have been reported?
According to the CDC, the number of patients of breakthrough infection that has been reported in the United States by April 30 days from January 1, 2021 is 10,262 people is. Of these, 2725 were asymptomatic and 160 died. According to a CDC study , the median age of infected individuals was 58 years and the median age of deaths was 82 years. Of the breakthrough infections reported in the United States from May 1 to July 19, 2021, 5601 were hospitalized and 1141 died. 'From a CDC study, patients who were hospitalized or died tended to be older, immunocompromised, or had pre-existing illnesses,' Inverse said.

◆ What are the symptoms?
'The symptoms of breakthrough infections range from completely asymptomatic to severe and can lead to hospitalization or death,' said Donald Arsendor, an associate professor of microbiology and immunology at Mehary Medical College. ' For people under the age of 65 without comorbidities, breakthrough infections are likely to be asymptomatic or mild.' The CDC also states that 'the chances of hospitalization and death are much lower than those who are not vaccinated.'

◆ Can breakthrough infections infect children with the virus?
In Japan and the United States, children under the age of 11 are not vaccinated against Pfizer & BioNTech and Moderna. Even those who have completed vaccination may infect their children with the virus, especially the Delta strain.

'For mutant strains other than SARS-CoV-2 and Delta strains, it was thought that infection would occur after about 15 minutes of close contact, but with Delta strains, infection occurs in a matter of seconds. It is very realistic for the Delta strain to be transmitted between parents and children who come into contact with the strain, but children under the age of 11 are much less likely to be more severe than adults. '

Regarding the infectivity of the Delta strain, which is said to be highly infectious, the CDC's (PDF file)

internal document reported by the Washington Post of an overseas newspaper states that the CDC considers it to be 'similar to chickenpox.' Became clear. The vertical axis of the table below shows the mortality rate, and the horizontal axis shows how many secondary infections a single infected person causes.

Regarding infectivity, 'Basic reproduction number, which indicates how many secondary infections an average person produces in a population that has no immunity to a certain infectious disease.' Or, 'Effective reproduction number', which indicates how many secondary infections an average of one infected person will produce at a certain time when the infection has already spread to the population, is a reference. Become. Regarding COVID-19, according to a study published in November 2020 in multiple countries, the basic reproduction number is 2.4 to 3.4. According to statistics from the Mathematical Model Center for Infectious Diseases, based at the London School of Hygiene and Tropical Medicine , the number of effective reproductions in the United States is 1.1-1.6 as of July 27, 2021. The basic reproduction number of Delta strain is 5 to 9.5, the basic reproduction number of measles is 6 to 7, and the basic reproduction number of 2009 influenza virus is 1.3 to 2.0. ..

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