I am following the latest developments on COVID-19 and our efforts to control the pandemic or to deal with it as an endemic disease. I will update this page regularly, so if you are interested, check back often.  As of May 14, 2022:

Another Study Shows Second Booster Effective in Preventing Serious COVID-19:  I think that most people should get the second booster dose (their fourth-dose of COVID-19 mRNA vaccination) because it is well tolerated and increases protection from serious disease by raising both cell and antibody immunity (Lancet Infectious Diseases, May 9, 2022). A randomized trial of 166 men and women, average age 70, who received their second booster dose of COVID-19 vaccination seven months after the first booster dose, showed a significant rise in anti-spike protein immunoglobulin (Ig)G titres and cellular responses measured 14 days after the injection.  The most effective laboratory tests to tell if you are protected from COVID-19 measure anti-spike protein antibodies and white blood cells that kill the virus. There was a significant drop in the anti-spike protein antibody approximately seven months after the first booster dose and before the second booster dose was given. The cellular (T-cell) responses were also raised considerably two weeks after the second booster dose. Pain and fatigue were the most common side effects, but no serious side effects were reported in this study. The authors think that antibody titers will drop as they did after the first booster injection, so it is likely that an additional booster injection will be recommended, probably a year after the second booster injection.

As of April 17, 2022:

Second “Booster Dose” Helps to Protect People over 60: After two initial Pfizer vaccine doses and one booster dose, a study showed that 182,122 adults ages 60 and over who received a second booster dose gained 52 percent protection against asymptomatic infection and 76 percent protection against COVID-related death 14 to 30 days after the booster was given (N Engl J Med, April 13, 2022). Protection against harm from COVID-19 increased as days after vaccination increased. The highest protection occurred at days 14 to 30 after receiving the second booster dose.

Boosters Reduce Hospitalization: The COVID-19 mRNA vaccines’ two-dose primary series appeared to provide less protection against hospitalization from Omicron variant infections than Alpha and Delta infections (JAMA, April 12, 2022;327(14):1323). A booster dose, however, was associated with increased effectiveness against Omicron hospitalizations at the same high levels achieved against earlier variants with two doses. The study included data from 11,690 adults admitted to 21 U.S. hospitals from March 11, 2021, to January 14, 2022. The two doses of vaccine increased prevention of hospitalization by 85 percent during Alpha and Delta infections, but only 65 percent during Omicron infections. Adding a third booster dose increased prevention of hospitalization to 86 percent. Vaccines reduced all types of COVID-19 severity significantly (BMJ, Mar 9, 2022; 376: e069761).

Most Reactions to COVID-19 Vaccine are Mild: The CDC reports that during the first six months of the U.S. COVID-19 vaccination program, most adverse events were mild and short-lived (Lancet Infectious Diseases, March 7, 2022). Almost 300 million mRNA vaccine doses were administered in the U.S. between December 14, 2020, and June 14, 2021 (JAMA, April 12, 2022;327(14):1323). Of the 340,522 reports of vaccine side effects, 92.1 percent were classified as non-serious; 6.6 percent as serious but not resulting in death; and 1.3 percent were deaths. The most common serious reports were shortness of breath, fever, fatigue, and headache. The most common cause of death was heart disease. The less serious reactions were more common after the second dose, compared to the first dose.

COVID-19 Vaccination Reduces Infectious Viral Load: Usually the more virus in a person infected with COVID-19, the more serious the disease. Viral load was measured in 600 infected symptomatic patients (Nature Medicine, April 14, 2022). The Delta variant caused a higher viral load than the original virus or the Omicron variant. Vaccination dramatically reduced viral load for Delta and Omicron infections, but a booster dose was necessary for the Omicron infections. Omicron’s very high infectiousness is caused by factors other than viral load alone.

As of April 10, 2022:

Who Should Get a Second COVID-19 Booster?  On Tuesday, March 29, 2022, the U.S. Food and Drug Administration authorized a second booster dose of the mRNA vaccines made by Pfizer or Moderna for all adults 50 years and older, to be given at least four months after the first booster of any approved COVID-19 vaccine. At this time, scientists do not have enough data to show that most people need to get this second booster dose. The primary concern is the highly contagious Omicron subvariant known as BA.2, which is now the dominant version of the virus in new U.S. cases (New York Times, March 29, 2022). The research data so far show that a fourth injection offers additional protection for people over 6o and those with conditions that impair their immune systems.

A study from Israel posted online this week, but not yet reviewed or published, reports that adults over 60 years of age who received a fourth injection were 78 percent less likely to die of COVID-19 than those who got only three injections. However, other studies show that a second booster has very limited benefits for healthy people under sixty and that a fourth dose did not raise antibody titers higher than it did after a third dose. Again, the person who is at high risk for serious disease is older or has a condition that can impair his immune system.

Who may need an mRNA booster now?
• a fourth injection for those who have received three doses of an mRNA vaccine from Moderna or Pfizer, and are over 60 or have an impaired immune system
• a third injection for those who received one dose of the Johnson & Johnson vaccine and a booster shot of an mRNA vaccine
• a third injection for those who received two doses of the Johnson & Johnson vaccine

Most likely, people who have had COVID-19 do not need a fourth injection because the highest and most effective immunity usually comes from having the disease, rather than from receiving the vaccine.

As of January 31, 2022:

Booster Dose Reduces COVID-19 Transmission and Infection: The initial, second and booster doses of the COVID-19 vaccines have been remarkably effective in reducing the disease’s infections, hospitalizations, intensive care admissions, intubations and deaths through the world (JAMA, Jan 25, 2022;327(4):327-328). The negative results of the vaccination programs are:
• lack of adequate vaccine distribution to everyone throughout the world
• unusual side effects of the vaccine in some people, but they are vastly less frequent than the number of lives saved by the vaccine
• unrealistically exaggerated fears of side effects from the vaccine by some people
• not getting vaccinated encourages the future emergence of variants that may partly resist vaccine-induced antibodies. Incomplete protection by the vaccine in some people with defective immunities causes them to carry the virus for prolonged periods that encourages more virus to be produced and increased risk for mutations that can become resistant to future vaccinations (mSphere, 2021;6(4):e0024421).

That same issue of the JAMA has an Israeli study showing a booster dose raises antibody titers higher and further reduces both symptomatic and asymptomatic COVID-19 infections (JAMA, Jan 25, 2022;327(4):341-349). The majority of health care workers who received two doses of the Pfizer vaccine had high protective blood antibody titers, but six months later, their protective antibody blood titers had lowered considerably. Some of the workers were given a third booster dose and were compared to workers who received only two doses of the vaccine. Those with a third booster dose were infected with the COVID-19 virus at a rate of 116 per 100,000 person-days prior to booster vaccination, compared to 2.8 per 100,000 after booster vaccination. That’s a relative reduction rate of 93 percent

The CDC now recommends a third booster dose six months after the two vaccine doses, preferably with an mRNA vaccine (Pfizer or Moderna). The U.S. Food and Drug Administration recommends a third dose of mRNA at least 5 months after the second dose for adolescents aged 12 to 15 years and for children aged 5 to 11 years who are immunocompromised.

As of January 12, 2022:

When Will COVID-19 Shift from Pandemic to Endemic? It now appears that the COVID-19 pandemic will not end with the virus disappearing, but with enough people gaining immunity from vaccination or natural infection that there will be much lower rates of hospitalization and death, even as the virus continues to circulate. Researchers from South Africa think that the Omicron variant of COVID-19 virus may help to end the pandemic to become endemic, another intermittent seasonal sickness similar to what happened to the 1918 Spanish Flu pandemic. The COVID-19 Omicron variant is more contagious, but causes fewer hospital and ICU admissions, much shorter duration of infection, and a lower death rate (Int J Infect Dis, Dec 28, 2021). The South African researchers found that with the wave of Omicron variant cases they had:
• a reduced death rate, just 4.5 percent of patients hospitalized with COVID compared to 21 percent with previous variants of COVID-19
• fewer hospital ICU admissions: dropped to one percent of patients from 4.3 percent
• fewer hospital admissions per cases of infection, which peaked at 108/day for the Omicron variant, compared with 213/day during the Delta wave
• Average length of hospital stays dropped to 4 days from 8.8 days

For comparison, in the Spanish Flu Pandemic (about 100 years ago):
• 500 million people or one-third of the world’s population became infected with this virus.
• 50 to 100 million died worldwide, including 675,000 U.S. citizens, making it one of the deadliest pandemics in human history.
• It had an unusually high death rate in younger (ages 20-40), healthy people.
• It recurred in four major waves.
Like the present COVID-19 pandemic, the 1918 H1N1 flu virus caused a cytokine storm in which a person’s own immunity attacks the human host as it is supposed to attack the invading virus. The fatality rates were among the highest ever, at about 4 percent, but there were no vaccines or effective treatments available at that time.

The COVID-19 pandemic was not caused by a more-virulent, more-lethal virus, it occurred because this virus had never before infected humans, so 100 percent of the human race could expect to become infected if they were exposed. The Omicron variant is more infectious and less damaging than the previous variants, so more people are likely to become infected without dying and thus have greater protection from future infections. People get significantly higher antibody titers from infections than from vaccinations, with infections providing 93 percent protection against a subsequent symptomatic infection and 52 percent protection against asymptomatic infection (Lancet, 2021, 397(10283):1459-1469). However, the protective antibodies do not last forever, and at this time we do not know how long they will last. When protective antibodies drop in the bloodstream, booster doses of the vaccine are likely to be needed to raise antibody titers again.

As of January 1, 2022:

Omicron Variant Less Damaging to Lungs: Coronavirus infections start in the nose or mouth and spread down to the lungs where they cause more severe disease. The highly contagious Omicron variant that is dominating COVID-19 cases today is milder than other variants because it appears to be far less damaging to the lungs and is more likely to stay in the nose and throat (Nature Portfolio, published online December 29, 2021). Recent research in animals shows that Omicron levels in the lungs were less than one-tenth of the level of other variants and grew significantly more slowly than other variants. This suggests that Omicron is more likely to cause an infection in humans that can produce a lasting immunity and is less likely to cause severe disease, hospitalization and death.

Obesity Increases Risk for Severe Symptoms and Death from COVID-19: A major breakthrough article from Stanford shows how being overweight when you have COVID-19 can cause the overactive cytokine storm that can kill you (bioRxiv, December 2021). This is the first article that shows that the COVID-19 virus infects human fat tissue, to cause immune cells in fat (macrophages) to release chemicals (cytokines) that cause inflammation that causes the cytokine storm in which a person’s own immunity attacks and kills their own cells in the same way that it would attack and kill an invading germ. The researchers found the coronavirus in fat cells near all the organs of people who had died from COVID-19. This shows that the corona virus, like the HIV virus, lives and thrives in fat cells and the immune cells in fat are attacking and destroying an infected person’s own organs. That means that obese people have the highest amount of fat and the highest amount of the virus that lives in fat and the highest amount of immune cells and cytokines that can attack and kill a person infected with COVID-19. This article could explain the high COVID-19 death rate in the United States which has a 42 percent obesity rate, among the highest obesity rates in the world.

Relationship Between Being Overweight and Severity of COVID-19: Symptoms of COVID-19 can vary from no symptoms at all, feeling like you have a cold, to the cytokine storm that causes extreme inflammation that destroys the lungs, kidneys, heart and other organs in the body (Nat Med, 2020;26:1017–1032). About 78 percent of people who have needed a ventilator or died from COVID-19 have been overweight or obese (Centers for Disease Control and Prevention, March 8, 2021). Being overweight markedly increases risk for a person with COVID-19 disease being hospitalized, in intensive care, intubated, and dying (Obesity, 2020;28:1195–1199; Intens Care Med, 2020;46:846–848; Ann Intern Med, 2020;173:773–781; Obes Rev, 2020;21:e13128). Obesity is a major risk factor for death from COVID-19 even in young healthy people who have no other obvious risk factors for disease (Obesity, 2020;28:1815–1825). The more you are overweight, the more likely you are to suffer severe COVID-19 disease (MMWR Morb Mortal Wkly Rep, 2021;70:355–361).

Weight Loss, Even From Surgery, Helps to Prevent Serious COVID-19 Symptoms: A study of 20,212 patients followed for 6.1 years (JAMA Surg, December 29, 2021) found that compared to obese people who have not had weight-loss surgery, people who were obese even after having had weight-loss surgery had:
• nearly half the risk of hospitalization for COVID-19,
• a 63 percent lower risk for needing supplemental oxygen, and
• a 60 percent lower risk for having a severe case of COVID-19.
They had less fat than those who had not had surgery. The surgical group also had a 53 percent lower 10-year risk of death from all causes and better control of blood sugar.

As of December 19, 2021:

COVID-19 Heart Damage Much More Common After Infections than after Vaccinations: A study of more than 38 million vaccinated people found that heart infections called myocarditis were far more likely to be caused by the infection than by vaccination (Nature Medicine, Dec 14, 2021). Oxford researchers evaluated cases of people with COVID-19 heart infections and irregular heartbeats from AstraZeneca-Oxford, Pfizer-BioNTech and Moderna. Researchers found that the 1 to 10 cases of myocarditis per million in people after the first or second vaccination compared to 40 extra cases per million in those who suffered from an acute infection with COVID-19. The researchers checked records of COVID-19 hospitalizations and deaths within 28 days of vaccination, or a recent infection (positive PCR test) for individuals 16 years and older, and those vaccinated between Dec. 1, 2020 and Aug. 24, 2021. Furthermore, the increased rate of myocarditis associated with mRNA vaccines from Pfizer and Moderna were found only in people younger than 40 years of age.

Longer Time Between COVID mRNA Doses Reduces Myocarditis Risk: A study from the University of Toronto and Public Health Ontario of 40 cases of myocarditis after 19.7 million doses of mRNA COVID-19 vaccine doses found that:
• The longer the time from the first to the second dose of the COVID-19 vaccine was associated with reduced incidence of myocarditis and that the rates of myocarditis were higher after the second dose than after the first dose (JAMA Network Open, Dec. 14, 2021)
• The rate of myocarditis was the same for the Moderna and Pfizer vaccines
• Rates of myocarditis were highest among young men, aged 18-24 years, following the second dose of mRNA vaccine
• No reported cases of myocarditis in males aged 18-24 years who received a first dose of Moderna’s mRNA-1273 followed by a second dose of Pfizer’s BNT162b2

Third Booster Dose of Pfizer Vaccine Markedly Reduced Severe Cases of COVID-19:  Two new studies from Israel show that the Pfizer booster lowers the risk for confirmed illness, severe illness, and death from COVID-19 (New Engl J Med. December 8, 2021).
• A Weizmann Institute of Science in Rehovot, Israel, study of more than four million patients found that the rate of COVID-19 infections was 10 times lower in booster-dosed patients in all age groups than in those who received only the first two injections. Booster-dosed people in all age groups also were around 20 times less likely to suffer severe COVID-19.
• A Tel Aviv study of more than 800,000 participants found that a third booster dose reduced death rate from COVID-19 by 90%.

Loss of Smell from COVID-19 is Usually Reversible: Researchers evaluated 97 patients who lost their ability to smell for more than seven days. Three months later, 84.3 percent recovered their smell. Eight months later, 96.1 percent had recovered their sense of smell (JAMA Netw Open, Jun 24, 2021).

High Rate of Asymptomatic Infections in COVID-19: A review of 95 studies that included nearly 30,000,000 cases of COVID-19, found that 0.25 percent of those tested had no symptoms ((JAMA Netw Open, Dec 15, 2021). The authors wrote that, “The high percentage of asymptomatic infections from this study highlights the potential transmission risk of asymptomatic infections in communities.”

As of December 4, 2021:

What the Experts Know So Far about the Omicron Variant:  The World Health Organization warns that the new COVID-19 variant, named Omicron, first reported to occur in southern Africa, has more than 30 mutations of its spike protein. It is too early to know whether these mutations increase severity or contagiousness of disease caused by the virus, COVID-19. However, the present vaccines are all made to attack the COVID-19 virus that does not have these mutations, so it may possibly cause more severe disease and be resistant to the approved vaccines already on the market. As a result, the United States, the European Union, Israel, Britain, Canada and other nations are limiting flights from South Africa into their countries, and other travel restrictions are likely. Several vaccine manufacturers are working on vaccines specifically for the new Omicron variant.

News of the Omicron variant should remind everyone to get their vaccinations and booster injections. This will help to reduce the number of people who become infected with COVID-19, and reduce the severity of infections that occur. Every time the virus infects a person it has the chance to produce new viruses, which increases the chances for new mutations. The more people who are infected with any variant of COVID-19, the more viruses are produced, increasing chances for more new mutations that may cause:
• more people to become infected,
• more severe disease in those infected, and
• more infections resistant to the presently-available vaccines.

As of November 29, 2021:

Vaccinations Decrease COVID-19 Infections, Severe Disease and Spread to Others:
• Infected vaccinated people are significantly less likely to develop symptoms and to develop severe symptoms, and they recover faster and are far less likely to be hospitalized than unvaccinated people (Lancet, 2021;398(10309):1407-1416).
• Vaccinated people can suffer severe COVID-19 disease, but they are far less likely to be hospitalized, spread the virus or die from COVID-19. The rate of hospitalization among US adults aged 18 years or older is 83.6 per 100,000 for unvaccinated persons compared with 4.5 per 100,000 for fully vaccinated persons (JAMA, 2021;326(20):2018-2020).
• A study of 4513 hospitalized COVID-19 adults in 18 US states found that unvaccinated patients accounted for 93.9 percent of those that progressed to intubation or death (JAMA, 2021;326(20):2043-2054).
• Vaccinated people are far less likely carry and spread the virus to other people (Science, Nov 2, 2021;eabl9551).
• A study showed that 287 vaccinated people were two-thirds less likely to be asymptomatic carriers than 164 unvaccinated participants (N Engl J Med, published online September 22, 2021).
• Viral loads in vaccinated people decline far more rapidly, and the virus that they shed is less likely to culture positive than virus shed by unvaccinated individuals (medRxiv, preprint posted September 2, 2021).
• Vaccinated people were less likely to spread COVID-19 including the delta variant (N Engl J Med, published online October 28, 2021).
• Nine months after people received the second dose of Pfizer or Moderna vaccines, neutralizing antibody titers to COVID-19 dropped to a tenth of their maximum levels. After they received a booster injection, antibody levels rose 25 times higher. Booster antibody levels were 50 times higher than those from natural infection (medRxiv, Nov. 21, 2021).

Benefits from Booster Shots:  A study of 306,710 Israeli adults 40 years and older found that, compared to those who had just two primary injections, the booster (3rd injection) markedly reduced COVID-19 infections, severity of infections and hospitalizations for the several weeks following the booster dose (JAMA Intern Med, published online November 30, 2021).

As of November 17, 2021:

Decontaminate Your Face Mask in your Oven: Masks are an essential part of limiting COVID-19 infections because the virus is spread mostly through respiratory droplets you breathe in from the air. Heating your disposable or long-lasting mask at 160 degrees Fahrenheit in your own oven for five minutes will kill the viruses that causes COVID-19, with no physical or chemical degradation of the masks (J of Hazardous Materials. November 7, 2021). Many other studies show that dry heat decontamination can effectively inactivate viruses without damaging protective equipment so they can be safely reused. This study shows that the same five minutes at 160 F degrees in an oven also kills many other viruses that live on furniture surfaces. Although ultraviolet light effectively kills viruses on flat or smooth surfaces, it was not effective in killing viruses in masks because it does not reach into folds and crevices. Chemical disinfectants can leave harmful residues and may also degrade mask material.

From November 11, 2021:

Unvaccinated People at Increased Risk for Developing Repeat Infections: Since COVID-19 hasn’t existed for long enough to perform a long-term study, researchers at Yale University and the University of North Carolina at Charlotte looked at reinfection data for six other human-infecting coronaviruses, including SARS and MERS, and found that unvaccinated people can expect reinfection in three months after an initial infection and they can be infected repeatedly every 16 to 17 months (The Lancet Microbe, October 1, 2021). They recommend repeat revaccinations for both people who have been infected with COVID-19 and those who have been vaccinated previously. A previous infection alone does not guarantee protection against another infection. The risk for COVID-19 reinfection is estimated to be about five percent at three months and 50 percent after 17 months.

As of October 26, 2021:

Available Laboratory Tests Will Not Tell You if You Need a Booster: The FDA lists 89 tests for immunity against COVID-19, but you can’t depend on any of these tests to tell you if you need a booster shot. Most of the available commercial blood tests do not measure protection against COVID-19 infection. They can tell if you have antibodies against COVID-19 in your bloodstream, but only some COVID-19 antibodies are effective in protecting you from infection. To find out if you may be protected, you would need to know how much neutralizing antibodies you have that will specifically kill the invading virus (Science, Aug 7, 2020;369(6504):643-650), and most blood tests are not dependable enough to do that. There is data to show that having higher levels of many different types of antibodies appears to offer greater protection against becoming infected with COVID-19 (Sci Rep, Mar 10, 2021;11:5538).

As of October 20, 2021:

Family Herd Immunity: To stop this pandemic of COVID-19 with herd immunity, more than 80 percent of the world’s population would have to be vaccinated or have had the disease. However, having even one member of your family immunized will help to protect you from getting the disease and possibly dying from it. A study of 1,789,728 people from 814,806 families in Sweden (JAMA Internal Medicine, October 11, 2021) found that:
• Family members without immunity had a 45-97 percent reduced risk of contracting COVID-19 as the number of immune family members increased.
• In families with two people living together, having one of them immunized reduced the rate of infection in the other person by 45 percent.
• In two to five-member families, each additional immunized person reduced the rate of infection in the non-immunized members dramatically.
• In five-member families, having four members immunized reduced the chances of the fifth member developing an infection by 97 percent.

Long COVID Syndrome: More than half of the 236 million people diagnosed with COVID-19 worldwide can be expected to suffer from Long COVID Syndrome, with symptoms lasting for six months or longer (JAMA Network Open, October 23, 2021;4(10):e2128568). Researchers conducted a review of 57 studies that included 250,351 unvaccinated adults and children diagnosed with COVID-19 between December 2019 and March 2021. The participants in these studies had an average age of 54, and 79 percent had been hospitalized. Symptoms of long COVID syndrome can include weight loss, fatigue, fever, pain, decreased mobility, difficulty concentrating, anxiety, abnormal chest X rays, shortness of breath, chest pain, palpitations, hair loss, rashes, stomach pain, loss of appetite, diarrhea and/or vomiting.

Booster Doses for Pfizer and Moderna: Advisors to the Food and Drug Administration (FDA) voted unanimously to approve Moderna or Pfizer booster shots for people over 60 or with underlying health problems, or those with jobs or living situations that put them at increased risk for exposure to COVID-19 (FDA Briefing, October 14, 2021).

J&J Recipients Get Better Booster Response from Moderna or Pfizer: An NIH study compared the response to booster shots with the same or different vaccines than were received from their first shots from Pfizer, Moderna, or Johnson & Johnson, the three COVID-19 vaccines currently authorized in the U.S. (MDRXiv, October 14, 2021, not yet peer reviewed). The study found that using different vaccines as boosters appears to induce the same or increased antibody response, compared to using the same booster dose. People who had received the J&J single-dose vaccine and then received a Moderna booster had antibody levels rise dramatically higher than those who received a J&J booster. Mixing and matching booster shots of different vaccines appears to be safe, and this week the FDA is expected to start allowing people to receive a different vaccine as a booster than the one they initially received (New York Times, October 18, 2021).

Unlikely to Get COVID-19 from Contaminated Surfaces: A study from Canada found that your chances of getting COVID-19 from surfaces at the grocery store are very low. Researchers cultured surfaces for COVID-19 at four grocery stores for a month and had no positive cultures (Current Research in Food Science, Oct, 2021;4:598-602). They cultured handles of grocery carts, payment terminals, conveyor belts, deli counter surfaces and plastic and metal handles in frozen food sections. This study refutes earlier studies that found the virus on shopping carts and freezer doors. It does not show that the virus cannot live on surfaces, and suggests that following the rules such as sanitizing surfaces and wearing masks can help to keep the surface areas of grocery stores relatively free of COVID-19 virus. It now appears that COVID-19 is primarily a disease that is acquired from breathing virus-infected droplets indoors in places where lots of people congregate.

Differences in COVID Antibody Responses in Natural Infection Versus Vaccination: Both natural COVID-19 infections and vaccinations help to protect you from infections by causing you to produce:
• antibodies that bind to the virus, and
• protective memory B cells that can help you to make antibodies if you are infected later on.
Having an infection with COVID-19 appears to be more effective in giving you memory B cells that can continue to make antibodies for more than a year afterwards (Nature, Oct 7, 2021). Both vaccination and natural infection caused similar increases in memory B cells. After six months, a vaccinated person starts to lose memory B cells, so their body could then lose its ability to make protective antibodies. One year after having been infected with COVID-19, recovered patients continue to make new and potent memory B cells. However, the virus that causes COVID-19 can still cause disease if you are infected in the future, so it is safer to get the vaccination than it is to get an infection with COVID-19. Memory B cells for smallpox have lasted at least 60 years after vaccination, and those for Spanish flu may last for 100 years.

As of October 10, 2021:

Booster Doses Six Months after 2nd Pfizer Vaccination: Six to 18 months after you receive your second dose of the Pfizer vaccine, you may still be at risk for developing COVID-19, but you are highly protected from getting serious disease that can result in hospitalization, intubation and death. The CDC recommends a third booster dose of the Pfizer vaccine for people over 65, those with immune-compromising health conditions and those in high-risk environments.  Similar recommendations are expected soon for Moderna and J&J vaccine boosters. In my opinion, anyone who is concerned about his or her immune status should get a booster shot.

Six months after the second Pfizer COVID-19 vaccination, antibody levels and immunity drop significantly, even though the vaccinated person is still protected from serious disease. In a study from Quatar, six months after second vaccination 20 percnt were protected from disease and almost 100 percent were protected from serious disease, hospitalization and death (NEJM, October 6, 2021) . An Israeli study showed that protective blood antibody levels drop significantly six months after the second Pfizer immunization (also in NEJM, Oct 6, 2021).

When a virus or vaccine enters your bloodstream, your immunity produces antibodies that try to attack and kill the virus. However, antibodies have a limited lifespan and eventually disappear from your bloodstream. Both vaccinations and infections cause your body to produce memory B cells that can last for a lifetime, so the next time that virus tries to enter your cells, the memory B cells quickly respond by stimulating your immunity to produce large amounts of antibodies that try to kill that virus. Memory B cells for the Spanish flu are still present 100 years later and those for smallpox last more than 50 years.

Vaccinations produces greater amounts of circulating antibodies than natural infection, but the live virus that causes natural COVID-19 infections stays around in your bloodstream for a longer period of time than the vaccination and produces longer-lasting and more-potent memory B cells that can produce antibodies many years later. However, a natural infection can hospitalize and kill you, while vaccinations almost never do that (Nature, October 7, 2021)

Older entries can be found in the post titled Latest on COVID-19: Archive