- Growing evidence suggests spacing out COVID-19 doses further could boost the shot’s efficacy against infection and hospitalization.
- It may also reduce the risk of the rare side effect, myocarditis.
- The CDC has updated guidance for people ages 12 and older.
The Centers for Disease Control and Prevention (CDC) now recommends expanding the interval between the first two doses of the messenger RNA (mRNA) coronavirus vaccines for most people.
The CDC updated
But the CDC says some groups should still get the vaccine at the 21-day interval. These groups include people who are immunocompromised, adults over 65 years, and others who need rapid protection due to increased concern about community transmission.
Until today, the CDC had recommended that the first two doses of the Pfizer vaccine be separated by 21 days, and the first two shots of the Moderna vaccine be separated by 28 days.
Growing evidence suggests that spacing out the doses further could boost the shot’s efficacy against infection and hospitalization and reduce the risk of myocarditis.
Though this new dosing interval could ultimately improve the shot’s long-term effectiveness, it would also increase the time it would take for individuals to become fully vaccinated.
“Many institutions, regulatory centers, and scientific groups are working tirelessly to ensure these safe and effective vaccines are as safe and effective as they can be as hundreds of millions of data points come in from around the world,” saidDr. Mark Cameron, an infectious disease specialist and epidemiologist with Case Western Reserve University in Cleveland, Ohio.
When the vaccines rolled out in Canada and the United Kingdom, supply was limited, and many people had to wait between 8 and 12 weeks for a second dose to become available.
Though many individuals were concerned about the consequences of extending the interval between their first two doses, evidence ultimately showed that doing so improved immunity.
One
Cameron says the Advisory Committee on Immunization Practices (ACIP) has been reviewing the data out of Canada and the United Kingdom, where vaccine supply issues extended the time between the two mRNA shots to 8-plus weeks.
“They noted when 8 weeks had passed between mRNA shots, you could find increased antibody responses with decreased infection and hospitalization risk, as well as a reduction in numbers of the already rare cases of myocarditis in young adult males post-vaccination,” said Cameron.
The original 3- to 4-week dosing schedule was followed in order to get enough data to get emergency-use authorization as quickly as possible, saidDr. Amesh Adalja, an infectious diseases expert and a senior scholar at the Johns Hopkins Center for Health Security.
“There wasn’t anything magic about the 3- to 4-week [interval],” Adalja said.
It’s known that spacing out doses longer increases the immunogenicity. It takes time for the immune system to mount and maintain a durable immune response.
“If it’s too close, you sort of truncate that period of maturation that occurs after the first dose,” said Adalja.
According to Cameron, changing the dosing interval recommendations involves a rigorous process with multiple checks and balances across many institutions, regulatory centers, and scientific groups.
“The vaccine scheduling data set supporting any change needs to be of sufficient size and scope before changes can be approved and adopted,” Cameron said.
Under the original dosing intervals, young males had a low risk of myocarditis, or heart inflammation.
Myocarditis, from the mRNA vaccines, is thought to be related to the immune system causing issues in the heart tissue.
“By giving the vaccines in close proximity, the immune response from the first vaccine hasn’t completely evaded — and then you’ve now hit it with the second vaccine, which revs it up even more,” Adalja said.
通过分离的镜头更多的时间,你允许the immune response mounted after the first shot to cool down, so it’s doesn’t get overstimulated after the second dose and put someone at risk for myocarditis.
Adalja does not expect the 8-week interval to have much of an impact on the other side effects commonly reported after vaccination, like soreness at the injection site
Extending the dosing interval from 3 and 4 weeks to 8 weeks, the immunogenicity provided by the shots can be increased and the risk of myocarditis can be decreased.
The CDC has updated recommendations for when a person should get a second COVID-19 vaccine dose. Now the CDC recommends expanding the interval between the first two doses of the mRNA coronavirus vaccines for most people.
Growing evidence suggests that spacing out the doses further could boost the shot’s efficacy against infection and hospitalization and reduce the risk of myocarditis.
Regulatory organizations are still reviewing the evidence to identify the safest and most effective vaccination schedule.