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Weeks after saying COVID-19 vaccine doses could be spaced out up to four months apart , a national expert advisory group is now deliberating whether one shot alone is sufficient for people who have had COVID.
Several recent small studies suggest that a single dose of the Pfizer/BioNTech or Moderna shots can launch a rapid immune response in people previously infected with the pandemic virus.
The response is so strong, people with a known history of COVID are reporting vaccine side effects — fever, headache, chills and muscle and joint pain — more frequently than the never infected after the first dose. Normally, the second dose tends to be more prone to side effects.
“Somebody who has had COVID before seems to respond very quickly to a dose of vaccine,” said Dr. Caroline Quach-Thanh, a pediatric infectious disease specialist at the University of Montreal and co-chair of Canada’s National Advisory Committee on Immunization, or NACI.
“They respond as a naïve person would with their second shot,” Quach-Thanh said.
“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?”
Somebody who has had COVID before seems to respond very quickly to a dose of vaccine
Also not clear is whether a single dose would be sufficient for older people who were previously infected or those with compromised immune systems.
But a one-dose-after-COVID strategy, as France’s top health authority, and now Quebec, has recommended, could stretch vaccine supplies and, while the vaccines are generally well tolerated, spare people unnecessary side effects of a second dose, researchers said.
One small study found that after the first dose of the Pfizer or Moderna vaccines, antibody titers — the amount of antibodies within a person’s blood — of previously infected “vaccinees” were 10 to 45 times as high as those of vaccinees without previous immunity when measured at the same time points after the first dose. For example, 13 to 16 days post-first dose, they were 25 times as high.
And while the antibody concentrations of people who had never been infected increased by a factor of three after the second shot, “no increase in antibody titers was observed in the COVID-19 survivors who received the second vaccine dose,” the researchers from the Icahn School of Medicine at Mount Sinai in New York wrote, suggesting that a booster or second dose might be of little value.
Even then, the previously infected had more than six times the mean antibody levels after the second dose.
What explains the stronger response in the previously infected? The Pfizer and Moderna vaccines are both messenger RNA vaccines. They work by instructing the body’s cells to produce a piece of the spike-shaped protein that adorns the surface of the virus that causes COVID.
That triggers an immune response and, in response, the body produces antibodies to protect people from getting infected if the real virus enters their bodies.
If the body has already been primed by a past infection to recognize the spike protein, the immune cells respond more vigorously after the first shot of vaccine.
“There’s certainly the suggestion that if you have previously been infected, it’s kind of like having had your first dose” of vaccine, said Toronto infectious diseases specialist Dr. Andrew Morris.
The problem is that it’s not yet known how long those early differences in immune responses last or whether the same would hold true for older people. The Mount Sinai study involved mostly younger (mean age 40) healthy adults.
It’s also not known how durable the vaccine-based immune response will be. Six months? Longer? Less?
Quach-Thanh said the panel’s controversial decision taken earlier this month to recommend spacing shots out to up to 16 weeks to give more people a first dose now makes this “less of an emergency situation to tackle.” However, she said Quebec recently changed its approach, and now “anybody who had a previously confirmed COVID infection is only getting one dose of vaccine,” though the immunocompromised will still receive two.
But Quach-Thanh said most experts expect booster shots will become the norm in the future. It won’t be a matter of one and forever done. “Call it a booster dose, call it new vaccine against variants, call it whatever you want.”
There have been 941,000 confirmed infections in Canada, though the true number could be four times, even 10 times higher, based on how much testing is being done.
The Mount Sinai researchers suggested screening people for antibodies, if their infection history isn’t known. Others argue testing everyone for antibodies would seriously bog down the process. Rapid antibody tests can also produce false positive.
People could also have lower antibody levels after a COVID infection if they had mild or no symptoms. If someone was just found to be COVID-positive because there was mass screening in a long-term care facility they worked in, they may still need two full doses, Quach-Thanh suggested. “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?”
A large study from Denmark suggests that a prior COVID infection gives people around 80 per cent protection again re-infection, though protection was only 47 per cent for people 65 and older.
Still, reinfection can happen, Morris said — “it’s not as rare as people think” — and mutations are increasing the risk, making it important that people who have already caught COVID be vaccinated.
For younger people, a one-dose strategy may be a reasonable approach, “but I think we need more data,” Morris said.
“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.”
In Quebec, “I cannot tell you what will happen if someone really wants the second dose — will it be offered or not? In the end it’s not dangerous, it’s not a contraindication to receive two doses,” said Dr. Nicholas Brousseau, chair of Quebec’s immunization committee. “It’s just not necessary, and the dose will be better used as a second dose for people who didn’t have COVID-19.”
Copyright Postmedia Network Inc., 2021