When the Pfizer and Modern COVID-19 vaccines were first available in December 2020, there was a strict recommended dosing schedule for inoculations.
People who received the Pfizer shot were advised to wait 21 days before receiving dose two and those who received Moderna waited 28 days. For the most part, people in the United States met this schedule, but in areas where supply was declining, people had to wait a few more weeks before accessing a second dose.
In the UK and Canada, for example, the limited supply meant that people often had to wait between eight and twelve weeks to get their second dose. Many people in this situation understandably understood how delaying the second dose would ultimately affect their protection, but the data would eventually show that extending the waiting period for the second dose was not a problem, and in fact it was beneficial.
“There’s a lot of evidence now that separating vaccines was a good idea to start with,” Monica Gandhi, an infectious disease specialist at the University of California, San Francisco, told HuffPost.
This is what we have learned about the distribution of COVID-19 vaccine doses.
Real-world studies and evidence have shown that extending the time between the first and second dose of Pfizer photos and Modern Improvement immunity.
A paper published in the journal Nature found that extending the duration between Pfizer doses to 12 weeks led to a more robust antibody response. Another recent study of the Mayo Clinic found that people who were vaccinated with Pfizer were more likely to have an advanced infection compared to those who received Moderna shots.
“Even four weeks made the difference instead of having three weeks between doses,” Gandhi said.
The real-world evidence of Canada and the United Kingdom, where vaccine shortages forced people to separate their doses for up to four months, compared to the United States and Israel (where there were many vaccines), also suggests that there is some additional protection to delay the second dose.
The effectiveness of the symptomatic disease vaccine “is lower in Israel and the United States, and both countries opted for a three-week strategy for Pfizer, while Canada and the United Kingdom have not reported a reduction in effectiveness of the symptomatic COVID vaccine, ”Gandhi said. (Note: Both vaccines, regardless of when the doses were given, are still over 90% effective against hospitalizations and death, which is what really matters.)
We often spaced doses with other shots.
Scientists studying the vaccines were not surprised to learn that widening the window between doses produced a better immune response.
“This has been known long before COVID-19,” he said Isaac Bogoch, physician and infectious disease scientist at the University of Toronto.
Many of the vaccines used to protect us from other infectious diseases have multiple doses separated by months. Because? Because vaccinology data generally suggest that extending the time between doses strengthens immunity.
A 2018 to study in messenger RNA (mRNA) vaccines prior to the pandemic, it was found that as doses of mRNA move away longer, the body creates stronger T-cell and B-cell responses (the other arm of the immune system that works alongside our antibodies).
This idea of extending the time between doses is not an accident, Bogoch said. “People will form a more robust immune response with separate doses,” he explained.
The two shots against hepatitis A are separated by six months. With the hepatitis B vaccine, the second dose is given four weeks after the first and the final dose is given eight weeks after the second. Children who get the measles and mumps and rubella vaccine routinely receive the second dose three months after the first, but nothing happens if they miss the exact time and come in a couple of months later.
You are still well protected.
That’s not to say you have to worry if you get your second dose of Pfizer 21 days after the first or second injection of Modern 28 days later. You are definitely still protected: the clinical trials of vaccines that were designed at these intervals show great effectiveness of the vaccine against serious diseases.
“It can give you the feeling that no matter how you do it, vaccines work well,” Gandhi said.
Bogoch added that it is not irrational, given the circumstances, for the doses for COVID-19 vaccines to be separated by a 21- to 28-day strait. If we had separated doses for several months, it would have taken much longer to conduct clinical trials and then vaccinate people and increase the immunity of the population in the midst of the global public health crisis.
Looking to the future, Bogoch said it would be fascinating to see what happens in populations that delayed their doses compared to populations that did not. This data will help inform future vaccination strategies and help us determine if and when to boost.
“To what extent does the separation of these doses provide greater protection, not only against infection, but also against severity?” Bogoch asked. “The most interesting thing is that it is a question that can be answered. That will be done. ”
Experts are still learning about COVID-19. The information in this story is what was known or available from the publication, but orientations may change as scientists find out more about the virus. Check with the Centers for Disease Control and Prevention for the most up-to-date recommendations.