Experts in immunology explain
A major component in developing herd immunity against SARS-CoV-2 (the virus that causes COVID-19) is how long the vaccination protects you.
If vaccination works well for a long time, it becomes feasible to adequately protect a major section of the population and in response eradicate or suppress the disease.
As vaccinations COVID-19 continue to be deployed, increased focus is paid to booster doses that are intended to increase immunity if it begins to decline. However, is a third dose necessary? And when, if so?
Let us look at how long COVID-19 immunity could endure, as the data tells us so far.
First of all, what do we know about immunity after being infected with COVID-19??
The appearance of antibodies against SARS-CoV-2 are used to assess immunity, with higher levels indicating more protection. When antibody levels fall below a certain threshold or disappear entirely, the person is in danger of reinfection.
However, we have just discovered evidence of long-term immunity, with antibody-forming cells in the bone marrow detected seven to eight months after infection with COVID-19. Furthermore, scientists have found signs of memory T cells (a form of immune cell) more than six months after infection.
Up until November 2020, a study of more than 9,000 treated COVID-19 patients in the United States found a 0.7 percent reinfection rate. These results are consistent with a somewhat more recent study that found reinfection after COVID-19 is extremely rare, at least temporarily.
Although some long-term immunity appears to be there following COVID-19 infection, vaccination is still recommended if you have had COVID.
There is some evidence that vaccination following recovery results in a higher level of immunity than “natural” immunity via disease or vaccine alone. People who have so-called “hybrid immunity” appear to have a more broad set of antibodies.
How long does vaccination immunity last?
There are two types of COVID-19 vaccines used in Australia and much of the Western world.
Pfizer and Moderna’s vaccines are based on mRNA technology. The messenger RNA instructs your cells to manufacture the coronavirus spike protein temporarily, training your immune system to protect you if you come into contact with the virus.
Despite ongoing trials, there is insufficient evidence on the longevity of the antibody response with viral vector vaccines. The original findings demonstrated efficacy for one to two months, but more research is needed to determine the extent of protection and if a booster will be required.
Interestingly, a vaccine identical to AstraZeneca against a similar coronavirus (MERS, or Middle East respiratory syndrome) exhibited stable antibody levels throughout a 12-month follow-up interval. This gives reason to believe that identical coronaviruses will be protected in the future.
The COVID-19 vaccines from Pfizer and Moderna are the first mRNA-based vaccines to be authorized for human use. However, more research is needed to determine the type and durability of the immunity they produce.
Notably, “germinal centers” have been discovered in the lymph nodes of persons who received the Pfizer vaccination. These serve as training centers for immune cells, training them to identify SARS-CoV-2, suggesting the possibility of long-term protection.
Although preliminary studies only investigated short-term efficacy, new research has demonstrated that six months of antibody activity was strong.
What do we know about Delta?
Delta variants, which are more contagious and potentially hazardous, are prone to draw attention towards booster programs.
All vaccinations have shown slightly reduced efficiency against Delta, suggesting that any decline in immunity over time may be more troublesome than other variants or the original SARS-CoV-2 virus.
Both the Pfizer and AstraZeneca vaccines’ protection against the Delta variant diminished after three months, according to a recent abstract (a study that has yet to be peer-reviewed).
According to this study from the United Kingdom, the Pfizer vaccine showed to be 92 percent effective at 14 days after the second dosage in preventing persons from getting a high infection rate, but this declined to 78 percent by 90 days. At 14 days, AstraZeneca was 69 percent effective against the same measure, but this dropped to 61 percent after 90 days.
This study found that patients who have been vaccinated but become infected with Delta still carry significant levels of the virus (viral load). Third booster dosages will be critical in preventing these viruses from resurfacing and spreading.
Despite this, researchers are constantly looking at how decreasing immunity can affect protection against dangerous COVID-19 outcomes/complications.
Alright so, what’s next?
The positive findings from the testing of the third dose have been presented by Pfizer to enhance immunity, and the organization seeks official US Food and Drug Administration (FDA) approval for a booster.
The US has decided that third doses will be available to persons who received an mRNA vaccine eight months or more ago starting next month.
Many countries have already started implementing boosters. The drive to provide third shots has created ethical considerations in certain high-income countries, given most people worldwide are still not able to get a first or second dose.
— Covid Aid (@covidaidcharity) August 31, 2021
In response to the spread of the Delta strain, a lot of countries have approved booster dosages for at-risk patients.
In the future, Australia is expected to have a booster program. However, given the existing supply challenges, it is unlikely to happen for several months.