Two Dose Vaccine May be Offered to Those Previously Infected with COVID-19

Canada’s vaccine advisory committee has recommended a complete two-dose series of an approved COVID-19 vaccines for individuals who have been previously infected with the coronavirus.

The National Advisory Committee on Immunization (NACI) updated its recommendations Thursday, saying that “a complete series of a COVID-19 vaccine may be offered to individuals who have had confirmed SARS-CoV-2 infection.”

In making the recommendation, the advisory panel took into consideration data from real-world studies.

Some of those included the protective immune response that previous coronavirus infections provide against re-infection; how individuals that have been previously infected with the virus responded after one and two doses of a COVID-19 vaccine and “the safety of offering two doses” of an approved vaccine to them.

In a statement released Thursday, NACI Chair Dr. Shelley Deeks said, “The latest evidence and our understanding of immunology tell us that individuals who have been previously infected have adequate protection for several months after the infection, which is improved after the first dose of COVID-19 vaccine.”

While it is “not clear how this protection will translate against new variants” of the novel coronavirus, Dr. Deeks said that there are “many reasons that jurisdictions may offer, and individuals may choose, a complete series of two vaccines even after a previous infection, including [for] participation in activities or travel.”

Chief Public Health Officer Dr. Theresa Tam reiterated the same.

“At this point, those who have been previously infected do have an immune response that is enhanced by one or two doses of the vaccine,” Dr. Tam said.

However, the advisory panel also recommended that those who have been previously infected should wait “to receive a vaccine until they no longer have acute symptoms of COVID-19 and are no longer infectious to others.”

Other factors, such as the extent of COVID-19 transmission in the community, the circulation of variants of concern and an individual’s risk of exposure to the coronavirus and severe illness, should also be taken into account when deciding when to vaccinate, NACI said.

Meanwhile, a study published Wednesday showed that two doses of Pfizer or AstraZeneca‘s COVID-19 vaccine are nearly as effective against the highly transmissible Delta coronavirus variant as they are against the previously dominant Alpha variant.

The study, published in the New England Journal of Medicine, confirmed two doses of Pfizer’s shot were 88 percent effective at preventing the symptomatic disease from the Delta variant, compared to 93.7 percent against the Alpha variant.

“Only modest differences in vaccine effectiveness were noted with the Delta variant as compared with the Alpha variant after the receipt of two vaccine doses,” Public Health England (PHE) researchers wrote in the study.

Data from Israel has estimated the lower effectiveness of Pfizer’s shot against symptomatic disease, although protection against the severe disease remains high.

PHE had previously said that the first dose of either vaccine was around 33 percent effective against symptomatic disease from the Delta variant.

The full study published on Wednesday found that one dose of Pfizer’s shot was 36 percent effective, and one dose of AstraZeneca’s vaccine was around 30 percent effective.

“Our finding of reduced effectiveness after the first dose would support efforts to maximize vaccine uptake with two doses among vulnerable groups in the context of circulation of the Delta variant,” the authors of the study said.


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