The length of immunity to COVID-19 caused by a vaccine is critical to the success of a long-term victory of the coronavirus pandemic, but experts say it still has yet to be determined how long this immunity will last.
mRNA vaccines, a relatively new form of technology, have proved popular, with the Pfizer/BioNTech shot receiving international support as governments and health authorities seek a way to end the pandemic and return to normalcy.
However, more than two months on since the vaccine’s first approval by the UK, scientists are still far from conclusively evaluating the length of immunity that mRNA vaccines induce in the human body against COVID-19.
“We [scientists] are already starting to see that that the mRNA vaccines will not really hold the promise to where to be the solution for COVID-19. We are already acknowledging that these vaccines are not as potent as we had hoped,” said Dr Ali Salanti, professor of immunology at the University of Copenhagen.
Even prior to the COVID-19 pandemic, mRNA vaccines had been around for at least a decade and, when going through clinical trials, had failed to induce a long-lasting immune response, but not all experts agree in regards to mRNA COVID-19 shot.
“We don’t really know yet what the length of protection of mRNA vaccines is [against COVID-19],” said Dr Paul Offit, member of the American Center for Disease Control (CDC) Advisory Committee on Immunization Practices. “I think the immunity will likely last for at least a couple of years.”
How long does vaccine-induced immunity against COVID-19 last?
Live vaccines generally induce longer lived immunity than other types of vaccines, according to the British Immunization Advisory Centre. However, there is virtually no data on where the mRNA vaccines fit in the spectrum of protection length.
So far, two companies have received international emergency approval for their mRNA vaccines against COVID-19: Pfizer/BioNTech and Moderna.
The Pfizer/BioNTech vaccine also remains the only COVID-19 vaccine across all vaccine types to be approved by the World Health Organization (WHO).
Marred with concerns over its vaccine potency, US-based pharmaceutical company Moderna issued a statement at a J.P. Morgan Healthcare conference in mid-January that its COVID-19 vaccine immunity is likely to last at least a year.
“When Pfizer and Moderna did their pre-approval phase trials, the protected efficacy was three-four months long,” added Offit. “I think it’s tens of millions of people who have been given the mRNA vaccine in the United States, so I think we’re going to learn pretty soon how long the mRNA vaccine-induced immunity lasts.”
Prior to the COVID-19 pandemic, mRNA vaccines proved to be insufficiently effective in late-stage clinical trials, which offers a partial explanation into their novelty in the medical market.
“They have simply not been good enough,” added Salanti. “And I would assume that we would have done the same if COVID-19 had not shut down societies. The reason these vaccines have been marketed is because they have proven to be effective in the short term.”
However, there is no scientific consensus on vaccine-induced length of immunity against COVID-19.
“We certainly know that people who develop natural immunity develop a fairly high frequency of memory immune cells, which suggests that immunity will be long lived. We also know that that's true with the mRNA vaccine,” added Offit.
Beyond mRNA: The future of a COVID-19 vaccine
Vaccine science continues to rapidly evolve amid the coronavirus pandemic, with new inoculations continuing to be announced. Manufacturers have already begun to announce improvements to vaccines, including mRNA vaccines, a trend that is likely to continue.
In mid-January, Moderna announced that it is likely to administer a third “booster” shot one year after the original two jabs of its COVID-19 vaccine, as the duration of protection of its vaccine against the virus is still unclear.
“No new vaccine or very limited number of vaccines have emerged that actually induce a long-lived memory response [to a disease]. With COVID-19, we don’t see long-lived immunity with neither the mRNA vaccines nor the recombinant [vector] vaccines” added Salanti. “The only exception is the HPV vaccine.”
Going forward, many scientists and vaccine researchers are suggesting combining vaccines of the first generation against COVID-19 in order to strengthen the length of immunity against the virus in second-generation vaccines.
“Right now, we're just trying to make predictions based on lab findings,” concluded Offit. “We will see how it practically plays out.”