NEW YORK – How long does the protection of vaccines against Covid-19 last?
Experts don’t know yet, as they continue to study vaccinated people to determine when the immunity may go away. The effectiveness of the vaccines against the newer variants will also determine whether additional injections are needed and when and how they should be administered.
“We only have information about how long vaccines have been studied,” said Deborah Fuller, a vaccine researcher at the University of Washington. “We have to study the vaccinated population and see where they become vulnerable to the virus again.”
Currently, the research from pharmaceutical company Pfizer indicates that the two-dose vaccine it developed with BioNTech remains highly effective for at least six months and probably longer. Those who received Moderna also maintain noticeable antibody levels for six months after receiving the second dose of the drug.
But antibodies don’t explain everything. To fight off invaders such as viruses, our immune system has another line of defense called the B and T cells, some of which can remain in the body long after antibody levels drop. If they encounter the same virus in the future, they can become active more quickly.
While they don’t completely prevent the disease, they can help reduce its severity. But at present, the exact role these “memory” cells could play against the coronavirus, and for how long, is unknown.
While current COVID-19 vaccines can be effective for about a year, they probably don’t provide lifelong protection like measles, said Dr. Kathleen Neuzil, a vaccine expert at the University of Maryland.
“It will be somewhere in the middle of that wide range,” he said.
Variations are another reason why an additional injection may be required.
Current vaccines are designed to target a specific spike protein in the coronavirus, said Mehul Suthar of the Emory Vaccine Center. If the virus mutates enough over time, they may need to be updated to increase their effectiveness.
At the moment, the vaccines seem to protect against the more well-known variants, albeit less visible in South Africa.
If it turns out that another injection is needed, a single dose can increase the protection of the current vaccines or contain the drug against one or more variants.
The need for a booster dose will partly depend on the success of the global vaccination campaign, the reduction of infections and the emergence of new variants.