The strategy to overcome attack with an ultra-short incubation period and escape with an ultra-long incubation period of the COVID-19 Delta variant of based on cases of outbreaks and their containment

ObjectiveTo discuss the strategy of fighting and containing COVID-19.

MethodThe speed of the spreading of the ordinary strain in Dalian on Dec. 15， 2021 caused by carrying cold-chain goods from a Russia-registered freighter and the Delta strain caused by imported cases in Guangzhou during May 20 to Jul. 23， 2021 was compared.

ResultsThe incubation period of the first generation of the imported Delta strain of COVID-19 was 4 days， which was 5 days shorter than that of the ordinary strain of COVID-19； The time from the exposure to the Delta strain to spreading to the next person was 1/3 days shorter than that of the ordinary strain of COVID-19. The inactivated vaccine needs at least 8 days for recall immune response meanwhile the mRNA vaccine needs at least 4 days， which could not completely block the COVID-19 virus， especially the Delta strain， which can attack with an ultra-short incubation period. Meanwhile， some COVID-19 strains have an incubation period longer than 14 days， which was another reason for the outbreak.

ConclusionThe time from the exposure to the COVID-19 Delta strain to spreading to the next person is 1/3 day shorter that of the ordinary strain of COIVD-19. Measures of full vaccination， physical quarantine and wearing masks in public should be taken to fight the epidemic of COVID-19， especially the Delta strain （or other variants） with an ultra-short or an ultra-long incubation period which can escape quarantine.