For a long time, studies from COVID-19 vaccine producers and public health regulators have suggested that the vaccinations’ protection diminishes over time.
Researchers from Moderna, which makes one of the two mRNA COVID-19 vaccines (the other is from Pfizer-BioNTech), report that people who were vaccinated within the last eight months had 36 percent fewer breakthrough infections than those who were vaccinated a year ago in a new study published on Sept. 15 to a preprint server—the study has not yet been peer-reviewed.
This shows that vaccination-induced immunity is at its peak shortly after people receive their prescribed two vaccine doses, and then begins to decline. The US Food and Drug Administration granted the Moderna vaccine emergency use authorisation (EUA) in December 2020; the FDA is presently considering the company’s request for full approval of the shot.
More than 14,000 people were randomly assigned to receive either two doses of the Moderna vaccine or two doses of placebo from July to October 2020, and more than 11,000 people were originally assigned to receive placebo doses from December 2020 to March 2021 and then chose to receive two doses of the Moderna vaccine after the EUA was granted.
88 people tested positive for COVID-19 in the latter group, which finished its two-dose regimen roughly eight months ago, compared to 162 people who had breakthrough cases in the earlier vaccinated group. This suggests that persons who were recently inoculated had a 36 percent lower chance of getting a breakthrough infection than those who were immunized a year earlier. (Only 19 of the 250 cases of breakthrough were serious.)
The findings, according to Moderna, indicate that protection diminishes over time, which is why the company applied to the FDA for approval of a booster dose to provide improved protection against COVID-19.
Moderna’s scientists published the results of another trial on Sept. 15 in the journal Nature Medicine, analyzing the efficacy of four different types of booster methods to support their case for an additional dose. In a short study of 79 participants, some received a third dosage of the same two-dose vaccine they already had, while others received a dose of a vaccine produced specifically for the Beta variation, a lesser dose of this Beta variant vaccine, and a combination of the original and Beta variant doses.
The findings showed that six months after participants were fully vaccinated with two doses, levels of antibodies that can neutralize the original SARS-CoV-2 reduced by roughly six to seven times. However, boosting with an additional dose of each of the four vaccines studied resulted in higher antibody levels about a month later. The combo dose was the most successful, boosting antibody levels by 46-fold against 16.7-fold with a third dose of current vaccine, 11.3-fold with the Beta-specific booster, and 9.2-fold with the lower dose Beta-specific booster.
Even against variations like Beta, Gamma, and Delta, these antibody levels reached or exceeded—in some cases by as much as 4.4 times—those produced in the first month after two doses of the vaccine, according to the researchers. This shows that the immune system remembers SARS-CoV-2, and that the booster can strengthen and speed up the immune response to build on the virus’s original protection and even fight versions that have mutated from the original type.
“We’ve been saying that we are going to have to have a variant booster, and that booster is going to have to be multivalent [and able to recognize different variants],” says Dr. Stephen Hoge, president of Moderna. “Then the clinical trial data came in … and we see a small benefit when we match a variant strain with the booster. But it’s not dramatic, and it’s not overwhelming benefit. In fact the [original] vaccine does really well against Delta.”
The idea is similar to the concept of a rising tide lifting all boats. The Delta variant, fortunately, has not learned to escape the immune system’s defenses; its success spreading among human populations has largely been because of its ability to flood the zone and quickly infect as many cells as possible in any unprotected person. Confronting that onslaught with an equally massive immune response, which, it seems, can be generated by a booster dose of the original vaccine, is sufficient to keep Delta at bay—and keeping any virus that does get through from causing severe disease.
Hoge says he is not worried so much about Delta, as about what might come after Delta. While the Delta variant hasn’t learned to escape the immune system yet, other variants, including Beta and Gamma, have shown signs of such evolution. If, over the course of the next few months, some of the known strains find a way to meld their respective strengths, the resultant variant could become a public health nightmare.
Moderna is working on a vaccine that would target Beta, Gamma and Delta, in case such a strain does actually emerge this winter. “The [mRNA] platform allows us to take a chance and get ahead of that possibility and be ready if we need it,” says Hoge. That booster could be ready and tested in a small group of people by the end of the year and available more widely in the first quarter of 2022 if needed, he says.
In the interim, Moderna has produced a vaccine that protects against the Delta variety, but according to Hoge, it is unlikely that it will be needed as a booster because the present vaccination can elicit an adequate increased immune response even against Delta.
Pfizer-BioNTech researchers, who also created an mRNA COVID-19 vaccine, have developed a Delta-specific vaccine and are evaluating it in the lab. However, infectious-disease experts are divided on whether a COVID-19 booster is necessary at this time.
While both Pfizer and Moderna have submitted data to the FDA in hopes of getting approval for an additional dose of their vaccines, and the White House COVID-19 team supports the notion, FDA specialists aren’t convinced.
The FDA recently published a report stressing the need for robust data to support the necessity for a booster dose ahead of a Sept. 17 advisory committee meeting of independent experts who will analyze the newest data on Pfizer-booster. BioNTech’s The FDA experts concluded that “currently US-licensed or permitted COVID-19 vaccinations still provide protection against severe COVID-19 sickness and death in the United States.” “While there are numerous potentially relevant studies, the FDA has not independently reviewed or verified the underlying data or conclusions.”