LOS ANGELES - A vaccine against the novel coronavirus will likely not be as simple as a quick shot from the doctor at your local pharmacy.
Evidence and continuing studies are suggesting that people may need two doses, not just one in order for the vaccine to be effective.
“We are applying that knowledge to determine rapidly the very best way to produce an effective, long-lasting vaccine against a new virus by testing strategies that have worked before and refining our vaccines and vaccination schedules as we learn more about the immune system’s response to COVID-19 and to vaccines that work in different ways,” Kelly Moore, the associate director for immunization education with the Immunization Action Coalition (IAC), said.
Operation Warp Speed (OWS), the federal government’s expedited mission to create and distribute a vaccine, aims to deliver 300 million doses of a safe, effective vaccine for COVID-19 by January 2021.
Of the six pharmaceutical companies given money to develop a vaccine, two of those companies, Pfizer and Moderna, are in Phase 3 clinical trials.
Pfizer and Moderna’s current Phase 3 trials are slated to enroll 30,000 volunteers in each trial, and each company is giving two doses — spaced out a month apart — to participating individuals.
AstraZeneca, another leading vaccine candidate, is expected to start trials soon. According to Reuters, the shot is “likely to provide protection for about a year, and the company is leaning towards a two-dose strategy for the potential vaccine.”
In Johnson & Johnson’s upcoming Phase 3 trials, the company is considering some participants take a single dose, while others do a double dose.
“As the Company plans its COVID-19 Phase 3 clinical development program, discussions are underway with partners with the objective to start a pivotal Phase 3 clinical trial of the single vaccine dose versus placebo in September, pending the interim data of the Phase 1 and 2 trials and approval of regulators. Simultaneously, the Company also is planning to start a parallel Phase 3 clinical trial of a two-dose regimen versus placebo,” Johnson & Johnson said.
Why two doses?
“If researchers believe two doses may be needed based upon their early animal studies, they measure the immune response in the blood of volunteer study participants in the early vaccine trials after the first dose and the second dose,” Moore said.
Researchers will be able to see if a second dose produces a much stronger immune response than the first dose, which would suggest that the recipient may be protected better and longer from disease than the first dose.
According to trials thus far, there is a strong likelihood that the vaccine will be given in a series, about a month apart, and may even require a booster several years later.
“The process of vaccination is literally teaching your immune system to recognize and react to a dangerous virus when it sees the virus. The first dose triggers important immune system changes, sometimes called ‘priming’ the immune response, and this process takes about two or three weeks. The second dose boosts that first immune response and the boosting process take about two weeks,” Moore said.
According to Moore, scientists will continue to choose certain intervals between doses based upon their experience and then study the immune response after different intervals under they have found a “sweet spot that produces the best immune response in the shortest amount of time for that vaccine.”
“If you give the two doses too close together, the immune response is not as strong,” Moore said.
Financial and logistical concerns
There are significant challenges to vaccinating a large proportion of the adult population against a virus using a two-dose vaccine.
While many vaccines already require two doses, including vaccines for chickenpox and Hepatitis A, two doses for a global vaccine could pose challenges financially and logistically.
There is concern over whether it will be difficult to convince individuals to get a vaccine not once, but twice.
In a poll by Gallup released Aug. 7, as many as one in three Americans said they would not get a vaccine for COVID-19 — even if the vaccine were FDA-approved and free of charge.
According to the poll, 65% of participants said they would and 35% said they would not.
“For a two-dose vaccine, people will need to make two vaccination visits in a month. This might mean time away from work or other obligations, depending on where and when they can be vaccinated,” Moore said.
“They need to understand that they are not protected until a week or two after their second dose, which might be five or six weeks after their first dose.”
The public will need to reminded that they cannot assume they will protected from infection after just one dose.
Moore said the public must be continually educated about the importance of getting two doses of vaccine and that it must be convenient and affordable for them to do so.
“We will need to focus on reminder systems, as we do with other vaccines that require two or 3 doses, to prompt people when it’s time to come back so they don’t forget,” Moore added.
The exact dosing will become clear over time, but another unknown is whether one round will even be enough.
While some vaccines like the measles make a person immune for life, others like influenza have different strains and require updated vaccinations each year.
Only testing will ultimately tell.
“I am especially encouraged to see how quickly people are volunteering to enroll in these clinical trials. Both companies that have started their Phase 3 trials in the United States have already enrolled more than half of the 30,000 volunteers needed. I hope this means we’ll begin getting answers about safety and about how well these vaccines work in a few months, ” Moore said.