Shortages of COVID-19 vaccine supply have left provinces, including Alberta, scrambling to adjust their rollout schedule, including plans for second doses.
There are questions over what will happen if a second dose is not administered in a timely manner and whether that decreases an individual’s protection.
READ MORE: Coronavirus vaccine rollout: How Canada compares with other countries
In Alberta, second doses of the vaccine are being offered within 42 days of the first dose, following a recommendation made by the World Health Organization and the National Advisory Committee on Immunization.
Chief medical officer of health Dr. Deena Hinshaw said the province was making this move to get first doses into as many Albertans as possible.
On Monday, Premier Jason Kenney said first dose appointments were being paused to ensure there was enough vaccine available for committed second dose appointments. Kenney also said second dose appointments would not be cancelled.
Are there enough doses to give everyone who had a first dose a second dose?
On Tuesday, Hinshaw said it seemed like there was enough vaccine in hand as well as what had been committed, even with the reduction in Pfizer supplies, to be able to offer that second dose to those who have booked it.
“At the moment, we don’t anticipate needing to push our second dose appointments past the 42 days,” she said.
READ MORE: Edmonton doctor says he was told he can’t book 2nd dose appointment for COVID-19 vaccine
However, several health-care professionals have told Global News that they have had issues with their second dose appointments.
One doctor said he was told his appointment had vanished, was told he could not book his second appointment and was not given a timeline for when he could book his second dose.
An Edmonton nurse who arrived at the vaccination site for her second dose was told there was a booking error and was also told appointments were not being booked right now.
On Tuesday, Hinshaw said some of the booking tools being built for the vaccine rollout were not quite ready when doses started arriving in December but the province had since shifted to a single booking tool run by AHS.
In a statement, AHS confirmed some eligible physicians and clinicians who booked first dose appointments earlier — manually — will be called back with details on their second dose.
“Due to uncertainty surrounding vaccine supply from the federal government, adjustments are being made to the COVID-19 vaccine implementation plan,” AHS spokesperson Kerry Williamson said.
“Some second dose appointments for eligible staff and physicians will need to be rescheduled.”
Is there a possibility some second dose appointments will not be fulfilled?
As of mid-afternoon on Jan. 20, AHS said 7,003 second doses had been administered.
Hinshaw, on Wednesday, said residents of long-term care and designated supportive living facilities would receive their second dose within the 21- to 29-day recommended interval.
She said other second doses would be given within the maximum allowable window of 42 days.
Alberta Health said the difference was the fact that those living in long-term care or designated supportive living are at a higher risk of severe outcomes.
Hinshaw said the province will do everything possible to get the second dose to individuals within the two time windows specified.
On Thursday, Alberta’s top doctor reiterated the province would do its “utmost” to ensure “that every individual who’s received their first dose does get their second dose within the 42-day timeline.
“If not, they’ll continue to be eligible and will receive it as soon as possible after that.”
Hinshaw said Alberta was working with the federal government and other provinces to use current allocations “as wisely as possible.”
She added that while there are many unknowns with the Pfizer and Moderna COVID-19 vaccines, health officials can consider evidence from other types of vaccines.
“We know that with other vaccines, that when someone has their first dose, there is no end date at which time they’re no longer eligible for a second dose,” Hinshaw said.
“And we know, sometimes, with some other vaccines, that if there is a little bit of a longer interval between first and second dose, the overall long-lasting immune response can sometimes be better.”
Will people be protected if they don’t get a second dose?
Dr. Ilan Schwartz, an infectious diseases professor at the University of Alberta, said it’s suboptimal.
“But we are working in a pandemic with a lot of unknowns and a lot of constraints,” he said.
Schwartz said, while there is data showing the initial vaccination is effective in mounting an immune response, there isn’t data for the full follow-up period if only one dose is administered.
“The exact timing of the second dose is probably not that important as long as it is within a few weeks of the recommended period,” he said.
According to the data from the clinical trials, Pfizer’s vaccine, which is 95 per cent effective, can offer partial protection as early as 12 days after the first dose.
READ MORE: Delaying second dose of coronavirus vaccines is ‘risky gamble’: experts
That protection can last for at least two months, according to Dr. Donald Vinh, an infectious disease specialist and a medical microbiologist at the McGill University Health Centre. A second dose is then required to achieve the vaccine’s full potential.
The data also showed that a second dose given 21 days later boosted the immune response, offering protection starting one week after the second jab.
Moderna’s vaccine, which also requires a second shot and has been shown to be 94 per cent effective, can mount protective antibody levels within two weeks of the first dose and last for at least three months, Vinh said.
Analyzing the clinical data for Moderna, Dr. Mark Siedner, infectious disease clinician at Massachusetts General Hospital, said that people who got the first dose and not the second had about a 50 per cent reduced chance of getting a symptomatic COVID-19 infection.
“So there is protection. It’s certainly better than not getting vaccinated,” he told Global News.
If there is a long delay between doses, will someone have to start the whole vaccination process again?
According to Schwartz, they don’t have to.
“The second dose, if it’s delayed, it shouldn’t result in the need to repeat the whole schedule again.
“I don’t think we’re going to have enough vaccine supply to be able to do that,” he said.
A statement by the NACI says there is no data available on the maximum interval between doses or on medium- or long-term efficacy of COVID-19 vaccines.
“In general, interruption of a vaccine series resulting in a greater than recommended interval between doses does not require restarting the series as delays between doses do not result in a reduction in final antibody concentrations for most multi-dose (prime-boost) products,” reads the statement.
“If administration of the second dose of a COVID-19 vaccine is delayed, the second dose should be provided as soon as possible.”
If supply issues persist, are there any other options?
Schwartz said there aren’t any at the moment but there are a couple vaccines that could be coming down the pipeline and which could potentially be approved in the next few months – the Oxford AstraZeneca vaccine and the Johnson and Johnson vaccine.
-with files from Saba Aziz
Comments