Increase knowledge | Has the delta virus incubation period extended?

Can family transmission be prevented?

　　The Paper Journalist Hu Danping

　　The transmission chain of this round of local epidemics has been extended again, and family transmission cases have reappeared.

　　On November 3, a family of five in Changping District, Beijing, was diagnosed with new coronary pneumonia.

The Paper combed through the official circulation information and found that the confirmed case 1 relapsed after being released from isolation as a second close contact, and the wife of case 1 in a family of 5 received the third shot of the new crown vaccine two days before the diagnosis.

　　Has the incubation period of Delta virus been extended after 5 days of isolation?

　　On November 3, the official WeChat account of the Beijing Municipal Health Commission notified a family of five who were diagnosed with new coronary pneumonia.

Case 1 was judged to be a secondary close contact who was transferred to a centralized isolation point for 5 days and then returned home. During the isolation period, his multiple nucleic acid tests were negative.

On November 1, after five days with his family, the wife, mother, daughter, and son of case 1 were all diagnosed with COVID-19.

　　Pang Xinghuo, deputy director of the Beijing Municipal Center for Disease Control and Prevention, introduced at a previous press conference that the viruses in the current round of the epidemic in Beijing are all Delta mutant strains, which are highly homologous to the viruses reported in recent cases in Inner Mongolia, Gansu and other places in my country.

　　On October 22, Case 1 was a close contact, that is, a close contact of a close contact, and had been isolated at a centralized isolation point for 5 days in accordance with regulations, and his multiple nucleic acid tests during the isolation period were negative.

　　According to the known transmission law of Delta virus, the average incubation period of the virus is 4.4 days, and most people will not exceed 7 days.

　　Is the incubation period of Delta virus prolonged?

On November 2, an epidemiologist told The Paper that three to four days is a common incubation period, that is, most infected people will develop symptoms or test positive within five days.

A small percentage of people will become ill or test positive after five days.

　　Judging from the incidence of this case, case 1 belongs to the small group of people who developed or tested positive after five days.

　　Whether it is necessary to extend the isolation period of second-time close contacts, the above-mentioned epidemiologists believe that the isolation period cannot be extended arbitrarily, which involves the control of prevention and control costs and the protection of the personal rights of the quarantined.

　　Even if the new crown vaccine is given, it is difficult to prevent family transmission

　　Officially released information shows that in the case of a family of five confirmed new crowns, the wife of case 1 received the third shot of the new crown vaccine two days before the diagnosis.

　　Can infection with the delta variant of the new crown virus be prevented in household transmission?

What are the effects of family members who have received the new crown vaccine?

　　"Delta mutant strains are difficult to prevent in home transmission." The above-mentioned epidemiologists said that the length of the delta incubation period is related to the infectious dose, that is, the number of inhaled viruses. The larger the infectious dose, the shorter the incubation period.

　　A study published in the latest issue of the international medical journal "The Lancet" shows that in household transmission, the effect of COVID-19 vaccination on preventing infection is not obvious.

　　On October 29, "The Lancet" published an article studying the impact of the new crown vaccine on the transmission and viral load of the Delta virus strain. This is the first time that relatively complete experimental data has been used to evaluate the vaccine's effect on the Delta mutant strain. The study of infection and virus dynamics.

　　The above article studied 621 people with mild new crown infections in the UK and found that people who received two doses of the vaccine can still transmit the virus to vaccinated and unvaccinated family members.

　　In families infected with the delta mutant strain, the infection rate of fully vaccinated was 25% (95%CI: [18%-33%]), while the infection rate of unvaccinated was 38% (95% CI: [24 %-53%]).

The peak viral load does not differ depending on the vaccination status or the type of mutation, but the peak viral load increases slightly with age.

　　This also means that fully vaccinated breakthrough infections have similar peak viral load to unvaccinated cases, and can spread the infection in the home environment, including to fully vaccinated contacts.

　　However, the study found that compared with those infected with the unvaccinated Delta mutant strain, the average viral load of those infected with the delta mutant strain decreased faster after vaccination.