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The Food and Drug Administration looks set to allow Americans to switch vaccines when choosing a Covid-19 booster shot. This authorization, which could arrive this week, is the latest development in a long-running debate. mix and match strategy Helps protect people from coronavirus.
Here are answers to some frequently asked questions about mixing and matching boost shots.
How is mix and match different?
Immunizations typically consist of two or more doses of the same vaccine. NS modern for example, the vaccine is administered in two identical mRNA shots four weeks apart.
A double dose can provide much more protection against an illness than a single shot. The first dose causes the B cells of the immune system to produce antibodies against a pathogen. Other immune cells, called T cells, enhance the ability to recognize and kill infected cells.
The second shot reinforces this reaction. B cells and T cells dedicated to fighting the virus multiply in much larger numbers. They also develop stronger attackers against the enemy.
In recent years, some vaccine researchers have tried switching from one vaccine to another for a second dose. This strategy is technically known as a heterologous prime-boost.
The pandemic has spurred further research into this possibility. One of the first heterologous prime-boost vaccines allowed for any disease. Sputnik V vaccine, It was developed last year by Russian researchers to prevent Covid-19. It uses two different adenoviruses to deliver coronavirus proteins, which the immune system then attacks. The first dose contains an adenovirus called Ad5 and the second contains another virus called Ad26.
Why mix and match can be better
Scientists have long suspected that heterologous prime-boosts sometimes work better than two identical doses. The designers of the Sputnik V vaccine were concerned that the first shot of Ad5 would generate antibodies not only against the coronavirus proteins it delivered, but also against Ad5 itself. A second shot of Ad5 could be cleared by people’s immune systems before increasing protection against Covid-19.
Research on experimental HIV vaccines has also suggested that mixing vaccines can elicit a broader, stronger response than multiple doses of a single vaccine. Different strains stimulate the immune system in different ways, and switching between the two vaccines can give people the best of both worlds.
The pandemic has given scientists new opportunities to test this idea. As the AstraZeneca vaccine spread rapidly in Europe, it turned out that young vaccinees carry a small but real risk of developing a blood clot. A second dose of Pfizer-BioNTech was offered to teenagers who had already taken a dose of AstraZeneca.
The two vaccines are completely different. formulation of AstraZeneca It is based on a chimpanzee adenovirus. Pfizer and BioNTech make their vaccines with mRNA. When the researchers looked at the immune response from this heterologous prime-boost, they found that it did. produced more antibodies Two shots of AstraZeneca alone.
A larger trial was conducted in the UK with 830 volunteers. Researchers gave some volunteers two doses of AstraZeneca vaccine, others two doses of Pfizer-BioNTech, and the rest a mix. They found no evidence that a heterologous prime-boost caused dangerous side effects. (Still their reportBritish scientists warned that their study was too small to detect rare problems.)
Mix-and-match can offer life-saving flexibility in a world where Covid-19 vaccines are hopelessly scarce. If people run out of supplies before they can get a second dose, they can switch to another vaccine and still have a strong immunity to the coronavirus.
What about Covid vaccine boosters?
Vaccines against some diseases require more than two shots in the so-called primary series to achieve the highest possible protection. In other cases, an additional booster shot is required after the primary series to restore mark immunity.
Over the summer, both the Moderna and Pfizer-BioNTech vaccines began to show some loss of efficacy against infection, although they remained strong against hospitalization. But the Biden administration a push started For boosters to restore people’s immune responses.
While Pfizer and BioNTech conducted booster trials of their vaccines, Moderna conducted its own studies. Last month, the FDA authorized a Pfizer-BioNTech booster for certain groups of people who received two doses earlier this year. It is expected to do the same for Moderna this week.
Johnson & Johnson has decided to use a single dose for its vaccine, which has proven less effective in clinical trials than Moderna or Pfizer-BioNTech. A study A study published last month found that the Johnson & Johnson vaccine was 71 percent effective against hospitalization, compared to 88 percent for Pfizer-BioNTech and 93 percent for Moderna.
On Friday, FDA advisors voted in favor of approving a second dose of Johnson & Johnson vaccine as a booster to boost immunity in Americans taking the first dose. But as the FDA’s top vaccine regulator, Dr. Peter Marks said at the meeting that it is possible that the agency did not want people to receive the same vaccine as a booster.
The agency is considering adjusting the language on the labels of all three authorized vaccines to indicate that providers may administer a different authorized vaccine at their discretion.
How well do mix and match boosters work?
Heterologous prime-boost studies conducted in Europe earlier this year suggested that combination vaccines may still provide good protection against Covid-19. In June, the National Institutes of Health launched its own variation on these trials, looking at what happens when fully vaccinated people switch to a new vaccine for a booster.
From the University of Maryland School of Medicine, Dr. Kirsten Lyke Presented the first results of the experiment at the FDA meeting on Friday. The researchers recruited people who had received one of three vaccines allowed in the United States and then gave them one of the three vaccines as a booster. Over all, they compared nine groups of 50 volunteers each.
Dr. Lyke and colleagues found that switching boosters raises levels of coronavirus antibodies, no matter what combination people take. “Maybe these things will play well together,” he said in an interview. And switching to a new booster didn’t cause any notable side effects.
The results were particularly striking for people who initially received a Johnson & Johnson vaccine. Those who received the Johnson & Johnson booster only saw a four-fold increase in antibodies. Switching to the Pfizer-BioNTech booster increased antibody levels 35-fold. The moderna booster has increased them 76 times.
Dr. Lyke cautioned against making hasty conclusions from the results so far. The researchers hope that by next month they will find out how well different boosters raise T cells, not just antibodies. The Johnson & Johnson vaccine is likely to shine in these results.
What You Need to Know About Covid-19 Booster Shots
The FDA has allowed booster shots for a select group of people who are taking their second dose. Pfizer-BioNTech Get the vaccine at least six months in advance. This group includes: vaccine recipients aged 65 and over or living in long-term care facilities; adults at high risk of serious Covid-19 due to an underlying medical condition; healthcare workers and others whose jobs put them at risk. with people weakened immune systems they are eligible to receive a third dose of Pfizer or Moderna four weeks after the second shot.
The CDC said conditions that qualify a person for a booster shot include: hypertension and heart disease; diabetes or obesity; cancer or blood diseases; weakened immune system; chronic lung, kidney, or liver disease; dementia and some disabilities. Pregnant women and current and former smokers are also eligible.
The FDA has allowed boosters for workers whose jobs put them at risk of exposure to potentially infectious humans. The CDC says the group includes: emergency health workers; education workers; food and agricultural workers; manufacturing workers; correction workers; US Postal Service employees; public transport workers; grocery workers.
Yeah. The CDC says the Covid vaccine can be administered regardless of the timing of other vaccines, and many pharmacy sites allow people to schedule a flu shot at the same time as a booster dose.
“We’re going to get a more rounded picture,” he said.
Will there be other booster options?
It’s totally possible. More than 100 Covid-19 vaccines currently being tested in clinical trials and more on animals. Adam Wheatley, an immunologist at the University of Melbourne in Australia, predicted that some of these new vaccines could prove to be superior boosters.
Unlike vaccines made from mRNA or adenoviruses, vaccines from companies like Sanofi-Pasteur and Novavax contain large amounts of viral protein.
Dr. “I suspect protein boosters would be really good,” Wheatley said. “When you arrive in the body with a relatively large protein breakdown, it results in a fairly robust recall of antibody responses.”
Sanofi-Pasteur spokesperson Nicolas Kressman said the company has gone too far in protein-based vaccine trials as a booster for people who have received other vaccines before. “Our goal is also to develop our vaccine as a universal booster that can boost immunity regardless of the initial vaccine received,” he said.
It is not yet clear how many Covid-19 boosters we will need to achieve long-term protection. It may be thought that a single shot may be sufficient. However, Covid-19 vaccines may need to be given every year, just like a vaccine. seasonal flu vaccine.
If Covid-19 boosters become an annual event, then a mix and match strategy will help get more people vaccinated. It will be much easier for people to get vaccinated regularly if they don’t have to worry about getting their original vaccine vaccinated again.
The flu provides a precedent for this plan. Vaccine manufacturers produce a new batch of seasonal flu vaccine each year. Some are inactivated influenza viruses. Some contain live viruses that are too weak to make humans sick. Others are made only from proteins derived from influenza proteins. Centers for Disease Control and Prevention, no choice what age people get the flu vaccine.
This kind of flexibility can also lower the price of boosters.
Dr. “Cost issues will definitely play a role,” Wheatley said. “Once you keep up with your local CVS, they may not carry the Pfizer shot and you may need to get the Sanofi product as that’s what’s more cost effective.”
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