Moderna said Thursday that people will probably need a booster shot of its two-dose COVID-19 vaccine before winter to ensure continued protection against worrisome viral variants, including Delta, but some vaccine experts are unconvinced.
While the vaccine is still strongly protective, Moderna said an analysis of blood samples from vaccinated people showed that levels of virus-neutralizing antibodies began falling six to eight months after a second shot and “will continue to wane and eventually impact vaccine efficacy.” As a result, the Cambridge drug firm said, “we believe [a] dose 3 booster will likely be necessary prior to the winter season.”
Moderna has tested a third dose of its vaccine at half the original 100 micrograms and found it boosted neutralizing antibodies back to high levels. The company is also testing a 100-microgram booster shot and expects to have results in the coming weeks.
Stephen Hoge, Moderna’s president, said the company hopes COVID-19 recedes as a public health crisis, but believes it will likely become an endemic disease that can be controlled with annual shots, much like the seasonal flu.
“We really do believe the virus is here to stay for the long term,” said Hoge, who leads research and development at Moderna.
In addition to testing booster shots, Moderna is working on an annual combined shot to prevent COVID-19, seasonal flu and respiratory syncytial virus, a common contagious virus that infects the lungs and breathing passages.
But Dr. Paul Offit, a prominent vaccine expert, said it was premature for Moderna to say a booster shot will be necessary in the fall.
“Moderna is a pharmaceutical company, not a public health agency,” said Offit, a pediatrician specializing in infectious diseases at Children’s Hospital of Philadelphia who sits on the advisory committee to the Food and Drug Administration that cleared Moderna’s vaccine and two others for emergency use. “It’s not for them to say.”
It’s not surprising that antibody levels induced by the vaccine declined over time, Offit said, but he noted that that alone may not be meaningful. There are other components in the immune system, including T cells and B cells, and even lower antibody levels may be high enough to protect people.
The bigger question is whether COVID-19 vaccines are still preventing infections that lead to severe symptoms and death, Offit said — and they do.
Of the 346 vaccinated people known to have developed breakthrough infections in an outbreak last month in Provincetown, he said, only four, or 1.2 percent, were hospitalized.
“When it gets to 5 percent, 10 percent, 15 percent, that tells you that critical immunity is fading,” Offit said. “But you haven’t seen that yet.” Overall, he said, breakthrough infections in vaccinated people remain rare and relatively mild.
Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Texas, said he has predicted all year that a booster shot will be needed at some point. But he has yet to see scientific data showing that it needs to happen in the fall, so soon after many Americans will have received their second doses.
He also said some people might need a booster shot more than others, including individuals over the age of 60 and those taking drugs that affect their immune responses, such as medicines for cancer.
”It’s important to clarify what your goals of a third immunization are,” Hotez said.
Israel’s prime minister recently announced that it would offer a coronavirus booster to people over 60 who have already been vaccinated, the first country to provide a third dose of a Western vaccine to its citizens on a wide scale. However, the World Health Organization on Wednesday called for a moratorium on booster shots until at least the end of September, saying billions of people in poor countries haven’t gotten their first dose yet.
During an earnings call Thursday, Moderna said its latest analysis of clinical trial data showed that the vaccine remained highly effective six months after the second shot, dipping to 93 percent from the 94 percent that the company trumpeted when it first went public with results in November.
The data came from an updated analysis of its late-stage trial, which began in July of last year and recruited 30,000 volunteers in the United States. The new results have yet to be published in a peer-reviewed scientific journal
Importantly, the results were tallied in March, before the emergence of the Delta variant in the United States, which is now blamed for the majority of new infections and is also fueling a rise in breakthrough cases.
Pfizer and its German partner, BioNTech, developed a similar coronavirus vaccine using two doses of messenger RNA technology. That vaccine was cleared for emergency use on Dec. 11, a week before Moderna’s. Pfizer representatives met with federal officials last month to advocate for a booster shot.
The efficacy of the Pfizer vaccine fell from 96 percent to 84 percent over six months, according to data released last week, although some experts have questioned whether that result was reliable. That data collection also ended before Delta became dominant..
White House chief medical adviser Dr. Anthony Fauci and other federal public health officials have said that no booster shot is needed yet.
Pfizer’s vaccine was the first authorized by drug regulators. Johnson & Johnson got a third coronavirus vaccine, which uses different technology, cleared in February.
The vaccine has proved good business for Moderna. On Thursday the company reported net income of almost $2.8 billion on revenue of $4.4 billion for the quarter ending June 30. Almost all of that came from its COVID-19 vaccine, the company’s first product to get to market in its 11-year history. Moderna’s stock has almost quadrupled year to date, from $111.73 on Jan. 4 to $416.26 Thursday. The biotech’s market value now stands at more than $163 billion.
The company’s workforce has expanded to 1,800 since the pandemic, roughly double what it had a year ago.
Moderna said it hopes to harness its mRNA delivery system for other treatments and vaccines. It has drug candidates in clinical development for five categories of illness: infectious disease, heart disease, oncology, rare diseases, and autoimmune disorders.
While traditional vaccines carry a dead or weakened virus into the body to stimulate an immune response, mRNA vaccines use custom-made messenger molecules that tell cells to create a viral protein. In the case of COVID-19, the Pfizer and Moderna vaccines instruct cells to create the distinctive spike protein on the surface of the coronavirus. Once that happens, the body’s immune system generates antibodies to fend off the disease if the recipient is exposed to the virus.
Jonathan Saltzman can be reached at email@example.com.