We might find the answer by looking at other coronaviruses and there has been a number of studies to find out how long immunity lasts.
Let’s start looking at the common cold.
Findings in the study “The time course of the immune response to experimental coronavirus infection of man” (Link) shows that immunity against the common cold, only lasts for a short time.
After 1 year much of the antibodies were gone, and 67 % got re-infected.
Please note the levels of IgG at figure (C) below.
(IgG is the most common type of antibody in the blood. They protect against infection by “remembering” which virus we’ve been exposed to before, so our immune system knows to attack them.)
The white dots show the average levels for the people that didn’t become infected when exposed to the virus at the first “challenge” (exposure).
The black dots show the average levels for the people that did become infected when exposed to the virus at the first “challenge” (exposure).
Some levels of antibodies are found in basically all people as we have encountered this type of cold by a coronavirus before.
A seen below, the people that did not get infected, (white dots), at their first exposure, had a higher starting level of IgG, indicating that they had had this cold more recent than the people that got infected.
For the ones that got infected, (black dots), the levels of antibodies rose quickly, but then fell quickly.
After 52 weeks the people that got infected 1 year earlier had returned to a low level of antibodies, but higher than they that did not get infected, and higher than what they had 1 year earlier.
One year after the first exposure, volunteers were again exposed to the same dose of coronavirus as they received one year before.
Now, of the people that did not get infected one year earlier, white dots, and now had a lower level of antibodies – 100% got infected.
Of the people that did get infected one year earlier, black dots, and now had a slightly higher level of antibodies – 67 % got infected, even though less severe.
This indicates that there still was a low level of protection for the people that had got infected 1 year earlier, but as the level of antibodies now had decreased significantly, the researchers conclude that “It indicates that protective amounts of antibody may have disappeared by 2 years”
Other studies have been conducted by looking at the SARS virus (properly named SARS-COV, whilst Covid-19 is named SARS-COV2.)
Whilst SARS is a worse sickness than the common cold, it is still a coronavirus, like COVID-19.
In the study “Duration of Antibody Responses after Severe Acute Respiratory Syndrome” (Link) they found that immunity only lasted for a limited time.
They studied people that had had SARS to see how long the antibodies would last looking at IgG and IgM.
(IgM antibodies are made by the body when you are first infected with new virus.
They are the first line of defence, and when the body senses a virus, the IgM level will rise for a short time. It will then drop as the IgG level kicks in to protect long-term.)
The levels of IgM rose quickly to peak at day 21-30 and to then have disappeared at day 90, whilst the long-term antibody IgG rose more slowly and peaked after 90-120 days at a value of 0.965 before it started to decline.
The figure below shows the level of antibodies at 6 months, 1, 2, and 3 years.
After 6 months, 100 % still had antibodies (IgG) and it had just declined slightly to 0.960
After 1 year, 100 % still had antibodies (IgG) and now it had declined to 0.638
After 2 years, 94.44% still had antibodies, however the levels had now dropped even further to 0.516.
When IgM reached its peak after 21-30 days, the level of IgG had at that stage reached 0.493. meaning that the level of antibodies after 2 years still were above that level, hopefully meaning that they would still be immune.
However, after 3 years only 55.55% still had antibodies, meaning that about 44% would now unlikely be immune.
The levels of IgG Antibodies had also dropped significantly to only 0.249, a value reached early on in the infection (around day 15) when the antibody IgM was still rising.
This could indicate that this value would not be sufficient to immunity even for the people with antibodies remaining.
Another study (Link) found that they after 6 years only could detect IgG antibodies in 8.7%
Memory B cell were not found in any.
(Memory B cells are required for every disease that we are immune against, so that we can make antibodies against it when we are exposed to it.)
This seem to indicate that none of them were immune.
The conclusion is that 2 years after SARS hopefully most would still be immune, whilst after 3 years, maybe less than 50 % and after 6 years maybe none.
We know that Covid-19 gives very different levels of sickness – so does the level of antibodies depend on the strength of the infection?
The simple logical answer would seem to be yes, but let’s look at some studies.
The 6-year study above found that 60 % still had Memory T cells.
(Memory T cells are used to mobilize the rest of our immune system, including Memory cell B and to provide a rapid response to a virus.)
They also found that “Patients with more severe clinical manifestations seemed to present a higher level of Ag-specific memory T cell response”, meaning that people that had been more sick had more T cells than people that had been less sick.
Further this Spanish study (Link) found that 44% of people that had had mild or asymptomatic infection had very low antibody levels, and that 22 % had so low levels that they could not see any difference from a person that never had had the infection.
In contrast the more severe cases had approximately 10 times more antibodies.
Both of these studies indicate that the level of antibodies will depend on the level of sickness.
The combined findings from these studies paints a picture that mild cases of coronavirus like the common cold and mild cases of COVID-19 either gives a very short time of protection, or maybe even no protection at all.
More severe cases (of SARS) seem to have give a protection for 2 – 3 years.
If this is true, it paints the picture that people with mild sicknesses don’t get immune for long, but that severe cases of sickness gives a longer immunity, however still not long.
This in turn could mean bad news for a vaccine, as if the sickness it self only gives a very short immunity, a vaccine might give even shorter immunity, if any.
This might be the sickness that humankind simply cannot easily overcome and the worst plague since black death.
However, there is always as solution, and that is upwards.
If we seek Jesus with all our heart, He is merciful and will always help, even though we don’t deserve it.
If my people, which are called by my name, shall humble themselves, and pray, and seek my face, and turn from their wicked ways; then will I hear from heaven, and will forgive their sin, and will heal their land.
This is what we need to do, and if we seek Jesus with all our heart, God will turn away this plague.
Disclaimer: This article is not written for medical advice, and cannot be used for medical advice, instead we refer you to your doctor for medical advice.