Ruminations: COVID Re-runs : One Vaccine Dose or Both?

"Somebody who has had COVID before seems to respond very quickly to a dose of vaccine. They respond as a naive person would with their second shot."
"The question that remains is that a one-size-fits-all for every previous infection? If you were asymptomatic at first infection, is it still OK?"
"Will the response to a first dose of vaccine be the same for everybody who has had a COVID infection before, regardless of the severity of disease?"
Dr.Caroline Quach-Thanh, pediatric infectious disease specialist, co-chair, National Advisory Committee on Immunization, Canada

"There's certainly the suggestion that if you have previously been infected, it's kind of like having had your first dose [of vaccine]."
"[Reinfection can happen] It's not as rare as people think [and mutations are increasing the risk such that people who have contracted COVID before should be vaccinated]."
"[For younger people, a one-dose strategy may be a reasonable approach] but I think we need more data."
"For older people, I think it's really unknown, and I think assuming you could get away with it is probably not necessarily so wise."
Dr.Andrew Morris, infectious disease specialist, Toronto

Credit: iStock, Bill Oxford

In Canada, its premier national expert immunization advisory group is in the process of deliberating whether one dose of vaccine only may be sufficient protection for those people who have already experienced a bout of COVID-19. Recently, a few small studies appear to conclude that a single dose of the Pfizer/BioNTech and Moderna vaccine could be useful in creating a rapid immune response in people who have previously been infected with the coronavirus.

People with a known history of having had COVID report more vaccine side effects -- including fever, headache, chills and muscle and joint aches -- than the never-infected, following the first dose. The second dose generally tends to be more intensely prone to side effects. It remains unclear whether a single dose would gain sufficient protection for older people who were infected previously, or those people with compromised immune systems.

France's elite health authority recommends a one-dose-after-COVID strategy, a recommendation that the province of Quebec has picked up for its effect in stretching vaccine supplies in this initial period of short supplies. The thought is there that while people appear to tolerate the vaccines, a single dose might also spare people unnecessary side effects by withholding a second dose, according to researchers.

It was found by one small study that following the first dose of a Pfizer or Moderna shot antibody titers -- meaning the amount of antibodies appearing in an individual's blood -- of those previously infected were seen to be ten to 46 times as high as those people being vaccinated who had no previous immunity after the first dose. They were 25 times as high 13 to 15 days following the first dose. Antibody concentrations of people never infected increased by a factor of 3 following the second shot "no increase in antibody titers was observed in the COVID-19 survivors who received the second vaccine dose" researchers from the Icahn School of Medicine in New York concluded, as they suggested a booster or second dose might offer little value.

Messenger RNA vaccines such as the Pfizer and Moderna models work by instructing the body's cells to produce a bit of the spike-shaped protein on the virus's surface, causing COVID. An immune response is then triggered to which the body responds by producing antibodies to protect against infection in the instance of the real virus entering someone's body. Once primed by a past infection to recognize the spike protein, the immune cells respond more vigorously following the first vaccine dose.

However, it is not yet understood how long those early differences in immune responses might last, much less whether older people would respond similarly. Nor how long a time the vaccine-based immune response would be effective. The advisory panel's controversial decision early in the month to recommend spacing shots out to up to 16 weeks in the interests of having more of the population vaccinated at least once places the new question into "less of an emergency situation to tackle."

Irrespective of which, according to most experts, booster shots are expected to represent the norm for the future which would see the regularization of annual vaccines to counter the coronavirus's anticipated season return and ongoing mutations. The Mount Sinai researchers suggested that people be screened for the presence of antibodies should infection history be unknown. Here too there are disagreements taking into account that people could have lower antibody levels following a COVID infection if they experienced mild or no symptoms at all.

Out of Denmark a larger study suggests that prior COVID infections endow people with up to an 80 percent protection rate against reinfection. There is, however, an age differential where people 65 and older were seen to have only a 47 percent protection against reinfection.